| Mapping | Rule Title | Description | Rationale |
|---|---|---|---|
| R1 | Install PAE Kernel on Supported 32-bit x86 Systems |
Systems that are using the 64-bit x86 kernel package
do not need to install the kernel-PAE package because the 64-bit
x86 kernel already includes this support. However, if the system is
32-bit and also supports the PAE and NX features as
determined in the previous section, the kernel-PAE package should
be installed to enable XD or NX support.
The kernel-PAE package can be installed with the following command:
$ sudo yum install kernel-PAEThe installation process should also have configured the bootloader to load the new kernel at boot. Verify this after reboot and modify /etc/default/grub if necessary. |
On 32-bit systems that support the XD or NX bit, the vendor-supplied PAE kernel is required to enable either Execute Disable (XD) or No Execute (NX) support. |
| R1 | Install the dracut-fips-aesni Package |
To enable FIPS on system that support the Advanced Encryption Standard (AES) or New
Instructions (AES-NI) engine, the system requires that the dracut-fips-aesni
package be installed.
The dracut-fips-aesni package can be installed with the following command:
$ sudo yum install dracut-fips-aesni |
Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated. |
| R1 | Ensure SMAP is not disabled during boot |
The SMAP is used to prevent the supervisor mode from unintentionally reading/writing into
memory pages in the user space, it is enabled by default since Linux kernel 3.7.
But it could be disabled through kernel boot parameters.
Ensure that Supervisor Mode Access Prevention (SMAP) is not disabled by
the nosmap boot paramenter option.
Check that the line GRUB_CMDLINE_LINUX="..."within /etc/default/grub doesn't contain the argument nosmap. Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --remove-args="nosmap" |
Disabling SMAP can facilitate exploitation of vulnerabilities caused by unintended access and manipulation of data in the user space. |
| R1 | Prefer to use a 64-bit Operating System when supported | Prefer installation of 64-bit operating systems when the CPU supports it. | Use of a 64-bit operating system offers a few advantages, like a larger address space range for Address Space Layout Randomization (ASLR) and systematic presence of No eXecute and Execute Disable (NX/XD) protection bits. |
| R1 | Ensure SMEP is not disabled during boot |
The SMEP is used to prevent the supervisor mode from executing user space code,
it is enabled by default since Linux kernel 3.0. But it could be disabled through
kernel boot parameters.
Ensure that Supervisor Mode Execution Prevention (SMEP) is not disabled by
the nosmep boot paramenter option.
Check that the line GRUB_CMDLINE_LINUX="..."within /etc/default/grub doesn't contain the argument nosmep. Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --remove-args="nosmep" |
Disabling SMEP can facilitate exploitation of certain vulnerabilities because it allows the kernel to unintentionally execute code in less privileged memory space. |
| R5 | Set the UEFI Boot Loader Password |
The grub2 boot loader should have a superuser account and password
protection enabled to protect boot-time settings.
Since plaintext passwords are a security risk, generate a hash for the password by running the following command: # grub2-setpasswordWhen prompted, enter the password that was selected. |
Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. |
| R5 | Set Boot Loader Password in grub2 |
The grub2 boot loader should have a superuser account and password
protection enabled to protect boot-time settings.
Since plaintext passwords are a security risk, generate a hash for the password by running the following command: # grub2-setpasswordWhen prompted, enter the password that was selected. |
Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. |
| R7 | IOMMU configuration directive |
On x86 architecture supporting VT-d, the IOMMU manages the access control policy between the hardware devices and some
of the system critical units such as the memory.
To ensure that iommu=force is added as a kernel command line
argument to newly installed kernels, add iommu=force to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... iommu=force ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="iommu=force" |
On x86 architectures, activating the I/OMMU prevents the system from arbitrary accesses potentially made by hardware devices. |
| R8 | Enforce Spectre v2 mitigation |
Spectre V2 is an indirect branch poisoning attack that can lead to data leakage.
An exploit for Spectre V2 tricks the indirect branch predictor into executing
code from a future indirect branch chosen by the attacker, even if the privilege
level is different.
Since Linux Kernel 4.15 you can check the Spectre V2 mitigation state with the following command:
cat /sys/devices/system/cpu/vulnerabilities/spectre_v2
Enforce the Spectre V2 mitigation by adding the argument
spectre_v2=on to the default
GRUB 2 command line for the Linux operating system.
To ensure that spectre_v2=on is added as a kernel command line
argument to newly installed kernels, add spectre_v2=on to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... spectre_v2=on ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="spectre_v2=on" |
The Spectre V2 vulnerability allows an attacker to read memory that he should not have access to. |
| R8 | Configure the confidence in TPM for entropy |
The TPM security chip that is available in most modern systems has a hardware RNG.
It is also used to feed the entropy pool, but generally not credited entropy.
Use rng_core.default_quality in the kernel command line to set the trust
level on the hardware generators. The trust level defines the amount of entropy to credit.
A value of 0 tells the system not to trust the hardware random number generators
available, and doesn't credit any entropy to the pool.
A value of 1000 assigns full confidence in the generators, and credits all the
entropy it provides to the pool.
Note that the value of rng_core.default_quality is global, affecting the trust
on all hardware random number generators.
Select the appropriate confidence by adding the argument
rng_core.default_quality=500 to the default
GRUB 2 command line for the Linux operating system.
To ensure that rng_core.default_quality=500 is added as a kernel command line
argument to newly installed kernels, add rng_core.default_quality=500 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... rng_core.default_quality=500 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="rng_core.default_quality=500" |
A system may struggle to initialize its entropy pool and end up starving. Crediting entropy from the hardware number generators available in the system helps fill up the entropy pool. |
| R8 | Enable randomization of the page allocator |
To enable randomization of the page allocator in the kernel, add the
page_alloc.shuffle=1 argument to the default GRUB 2 command line.
To ensure that page_alloc.shuffle=1 is added as a kernel command line
argument to newly installed kernels, add page_alloc.shuffle=1 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... page_alloc.shuffle=1 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="page_alloc.shuffle=1" |
The CONFIG_SHUFFLE_PAGE_ALLOCATOR config option is primarily focused on improving the average utilization of a direct-mapped memory-side-cache. Aside of this performance effect, it also reduces predictability of page allocations in situations when the bad actor can crash the system and somehow leverage knowledge of (page) allocation order right after a fresh reboot, or can control the timing between a hot-pluggable memory node (as in NUMA node) and applications allocating memory ouf of that node. The page_alloc.shuffle=1 kernel command line parameter then forces this functionality irrespectively of memory cache architecture. |
| R8 | Enable page allocator poisoning |
To enable poisoning of free pages,
add the argument page_poison=1 to the default
GRUB 2 command line for the Linux operating system.
To ensure that page_poison=1 is added as a kernel command line
argument to newly installed kernels, add page_poison=1 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... page_poison=1 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="page_poison=1" |
Poisoning writes an arbitrary value to freed pages, so any modification or reference to that page after being freed or before being initialized will be detected and prevented. This prevents many types of use-after-free vulnerabilities at little performance cost. Also prevents leak of data and detection of corrupted memory. |
| R8 | Disable merging of slabs with similar size |
The kernel may merge similar slabs together to reduce overhead and increase
cache hotness of objects.
Disabling merging of slabs keeps the slabs separate and reduces the risk of
kernel heap overflows overwriting objects in merged caches.
To disable merging of slabs in the Kernel add the argument slab_nomerge=yes
to the default GRUB 2 command line for the Linux operating system.
To ensure that slab_nomerge=yes is added as a kernel command line
argument to newly installed kernels, add slab_nomerge=yes to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... slab_nomerge=yes ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="slab_nomerge=yes" |
Disabling the merge of slabs of similar sizes prevents the kernel from merging a seemingly useless but vulnerable slab with a useful and valuable slab. This increase the risk that a heap overflow could overwrite objects from merged caches, with unmerged caches the heap overflow would only affect the objects in the same cache. Overall, this reduces the kernel attack surface area by isolating slabs from each other. |
| R8 | Prevent applications from mapping low portion of virtual memory |
To set the runtime status of the vm.mmap_min_addr kernel parameter, run the following command: $ sudo sysctl -w vm.mmap_min_addr=65536To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: vm.mmap_min_addr = 65536 |
The vm.mmap_min_addr parameter specifies the minimum virtual address that a process is allowed to mmap. Allowing a process to mmap low portion of virtual memory can have security implications such as such as heightened risk of kernel null pointer dereference defects. |
| R8 | Enable SLUB/SLAB allocator poisoning |
To enable poisoning of SLUB/SLAB objects,
add the argument slub_debug=P to the default
GRUB 2 command line for the Linux operating system.
To ensure that slub_debug=P is added as a kernel command line
argument to newly installed kernels, add slub_debug=P to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... slub_debug=P ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="slub_debug=P" |
Poisoning writes an arbitrary value to freed objects, so any modification or reference to that object after being freed or before being initialized will be detected and prevented. This prevents many types of use-after-free vulnerabilities at little performance cost. Also prevents leak of data and detection of corrupted memory. |
| R8 | Configure Microarchitectural Data Sampling mitigation |
Microarchitectural Data Sampling (MDS) is a hardware vulnerability which allows unprivileged
speculative access to data which is available in various CPU internal buffers.
When performing store, load, L1 refill operations, processors write data into temporary
microarchitectural structures (buffers), and the data in the buffer can be forwarded to load
operations as an optimization.
Under certain conditions, data unrelated to the load operations can be speculatively
forwarded from the buffers to a disclosure gadget which allows in turn to infer the value
via a cache side channel attack.
Select the appropriate mitigation by adding the argument
mds=full to the default
GRUB 2 command line for the Linux operating system.
To ensure that mds=full is added as a kernel command line
argument to newly installed kernels, add mds=full to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... mds=full ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="mds=full"Not all processors are affected by all variants of MDS, but the mitigation mechanism is identical for all of them. Since Linux Kernel 5.2 you can check whether the system is vulnerable or mitigated with the following command: cat /sys/devices/system/cpu/vulnerabilities/mds |
The MDS vulnerability allows an attacker to sample data from internal CPU buffers. |
| R8 | Force kernel panic on uncorrected MCEs |
A Machine Check Exception is an error generated by the CPU itdetects an error
in itself, memory or I/O devices.
These errors may be corrected and generate a check log entry, if an error
cannot be corrected the kernel may panic or SIGBUS.
To force the kernel to panic on any uncorrected error reported by Machine Check
set the MCE tolerance to zero by adding mce=0
to the default GRUB 2 command line for the Linux operating system.
To ensure that mce=0 is added as a kernel command line
argument to newly installed kernels, add mce=0 to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... mce=0 ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="mce=0" |
Allowing uncorrected errors to result on a SIGBUS may allow an attacker to continue trying to exploit a vulnerability such as Rowhammer. |
| R8 | Configure L1 Terminal Fault mitigations |
L1 Terminal Fault (L1TF) is a hardware vulnerability which allows unprivileged
speculative access to data which is available in the Level 1 Data Cache when
the page table entry isn't present.
Select the appropriate mitigation by adding the argument
l1tf=flush to the default
GRUB 2 command line for the Linux operating system.
To ensure that l1tf=flush is added as a kernel command line
argument to newly installed kernels, add l1tf=flush to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... l1tf=flush ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="l1tf=flush"Since Linux Kernel 4.19 you can check the L1TF vulnerability state with the following command: cat /sys/devices/system/cpu/vulnerabilities/l1tf |
The L1TF vulnerability allows an attacker to bypass memory access security controls imposed by the system or hypervisor. The L1TF vulnerability allows read access to any physical memory location that is cached in the L1 Data Cache. |
| R8 | Configure Speculative Store Bypass Mitigation |
Certain CPUs are vulnerable to an exploit against a common wide industry wide performance
optimization known as Speculative Store Bypass (SSB).
In such cases, recent stores to the same memory location cannot always be observed by later
loads during speculative execution. However, such stores are unlikely and thus they can be
detected prior to instruction retirement at the end of a particular speculation execution
window.
Since Linux Kernel 4.17 you can check the SSB mitigation state with the following command:
cat /sys/devices/system/cpu/vulnerabilities/spec_store_bypass
Select the appropriate SSB state by adding the argument
spec_store_bypass_disable=prctl to the default
GRUB 2 command line for the Linux operating system.
To ensure that spec_store_bypass_disable=prctl is added as a kernel command line
argument to newly installed kernels, add spec_store_bypass_disable=prctl to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... spec_store_bypass_disable=prctl ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="spec_store_bypass_disable=prctl" |
In vulnerable processsors, the speculatively forwarded store can be used in a cache side channel attack. An example of this is reading memory to which the attacker does not directly have access, for example inside the sandboxed code. |
| R8 | Enable Kernel Page-Table Isolation (KPTI) |
To enable Kernel page-table isolation,
add the argument pti=on to the default
GRUB 2 command line for the Linux operating system.
To ensure that pti=on is added as a kernel command line
argument to newly installed kernels, add pti=on to the
default Grub2 command line for Linux operating systems. Modify the line within
/etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... pti=on ..."Run the following command to update command line for already installed kernels: # grubby --update-kernel=ALL --args="pti=on" |
Kernel page-table isolation is a kernel feature that mitigates the Meltdown security vulnerability and hardens the kernel against attempts to bypass kernel address space layout randomization (KASLR). |
| R9 | Limit CPU consumption of the Perf system |
To set the runtime status of the kernel.perf_cpu_time_max_percent kernel parameter, run the following command: $ sudo sysctl -w kernel.perf_cpu_time_max_percent=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.perf_cpu_time_max_percent = 1 |
The kernel.perf_cpu_time_max_percent configures a treshold of maximum percentile of CPU that can be used by Perf system. Restricting usage of Perf system decreases risk of potential availability problems. |
| R9 | Configure maximum number of process identifiers |
To set the runtime status of the kernel.pid_max kernel parameter, run the following command: $ sudo sysctl -w kernel.pid_max=65536To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.pid_max = 65536 |
The kernel.pid_max parameter configures upper limit on process identifiers (PID). If this number is not high enough, it might happen that forking of new processes is not possible, because all available PIDs are exhausted. Increasing this number enhances availability. |
| R9 | Restrict Exposed Kernel Pointer Addresses Access |
To set the runtime status of the kernel.kptr_restrict kernel parameter, run the following command: $ sudo sysctl -w kernel.kptr_restrict=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.kptr_restrict = 1 |
Exposing kernel pointers (through procfs or seq_printf()) exposes kernel writeable structures which may contain functions pointers. If a write vulnerability occurs in the kernel, allowing write access to any of this structure, the kernel can be compromised. This option disallow any program without the CAP_SYSLOG capability to get the addresses of kernel pointers by replacing them with 0. |
| R9 | Limit sampling frequency of the Perf system |
To set the runtime status of the kernel.perf_event_max_sample_rate kernel parameter, run the following command: $ sudo sysctl -w kernel.perf_event_max_sample_rate=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.perf_event_max_sample_rate = 1 |
The kernel.perf_event_max_sample_rate parameter configures maximum frequency of collecting of samples for the Perf system. It is expressed in samples per second. Restricting usage of Perf system decreases risk of potential availability problems. |
| R9 | Disallow kernel profiling by unprivileged users |
To set the runtime status of the kernel.perf_event_paranoid kernel parameter, run the following command: $ sudo sysctl -w kernel.perf_event_paranoid=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.perf_event_paranoid = 2 |
Kernel profiling can reveal sensitive information about kernel behaviour. |
| R9 | Restrict Access to Kernel Message Buffer |
To set the runtime status of the kernel.dmesg_restrict kernel parameter, run the following command: $ sudo sysctl -w kernel.dmesg_restrict=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.dmesg_restrict = 1 |
Unprivileged access to the kernel syslog can expose sensitive kernel address information. |
| R9 | Kernel panic on oops |
To set the runtime status of the kernel.panic_on_oops kernel parameter, run the following command: $ sudo sysctl -w kernel.panic_on_oops=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.panic_on_oops = 1 |
An attacker trying to exploit the kernel may trigger kernel OOPSes, panicking the system will impede them from continuing. |
| R9 | Disable Access to Network bpf() Syscall From Unprivileged Processes |
To set the runtime status of the kernel.unprivileged_bpf_disabled kernel parameter, run the following command: $ sudo sysctl -w kernel.unprivileged_bpf_disabled=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.unprivileged_bpf_disabled = 1 |
Loading and accessing the packet filters programs and maps using the bpf() syscall has the potential of revealing sensitive information about the kernel state. |
| R9 | Disallow magic SysRq key |
To set the runtime status of the kernel.sysrq kernel parameter, run the following command: $ sudo sysctl -w kernel.sysrq=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.sysrq = 0 |
The Magic SysRq key allows sending certain commands directly to the running kernel. It can dump various system and process information, potentially revealing sensitive information. It can also reboot or shutdown the machine, disturbing its availability. |
| R9 | Enable Randomized Layout of Virtual Address Space |
To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command: $ sudo sysctl -w kernel.randomize_va_space=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.randomize_va_space = 2 |
Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques. |
| R10 | Disable loading and unloading of kernel modules |
To set the runtime status of the kernel.modules_disabled kernel parameter, run the following command: $ sudo sysctl -w kernel.modules_disabled=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.modules_disabled = 1 |
Malicious kernel modules can have a significant impact on system security and availability. Disabling loading of kernel modules prevents this threat. Note that once this option has been set, it cannot be reverted without doing a system reboot. Make sure that all needed kernel modules are loaded before setting this option. |
| R11 | Restrict usage of ptrace to descendant processes |
To set the runtime status of the kernel.yama.ptrace_scope kernel parameter, run the following command: $ sudo sysctl -w kernel.yama.ptrace_scope=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: kernel.yama.ptrace_scope = 1 |
Unrestricted usage of ptrace allows compromised binaries to run ptrace on another processes of the user. Like this, the attacker can steal sensitive information from the target processes (e.g. SSH sessions, web browser, ...) without any additional assistance from the user (i.e. without resorting to phishing). |
| R12 | Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.rp_filter kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.rp_filter=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.rp_filter = 1 |
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks. |
| R12 | Disable Accepting Packets Routed Between Local Interfaces |
To set the runtime status of the net.ipv4.conf.all.accept_local kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.accept_local=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.accept_local = 0 |
Configure net.ipv4.conf.all.accept_local=0 to consider as invalid the packets received from outside whose source is the 127.0.0.0/8 address block. In combination with suitable routing, this can be used to direct packets between two local interfaces over the wire and have them accepted properly. |
| R12 | Configure Sending and Accepting Shared Media Redirects for All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.shared_media kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.shared_media=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.shared_media = 0 |
This setting should be aligned with net.ipv4.conf.all.secure_redirects because it overrides it. If shared_media is enabled for an interface secure_redirects will be enabled too. |
| R12 | Enable Kernel Parameter to Use TCP RFC 1337 on IPv4 Interfaces |
To set the runtime status of the net.ipv4.tcp_rfc1337 kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.tcp_rfc1337=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.tcp_rfc1337 = 1 |
Enable TCP behavior conformant with RFC 1337. When disabled, if a RST is received in TIME_WAIT state, we close the socket immediately without waiting for the end of the TIME_WAIT period. |
| R12 | Enable Kernel Parameter to Use TCP Syncookies on Network Interfaces |
To set the runtime status of the net.ipv4.tcp_syncookies kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.tcp_syncookies=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.tcp_syncookies = 1 |
A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests. |
| R12 | Enable Kernel Parameter to Ignore Bogus ICMP Error Responses on IPv4 Interfaces |
To set the runtime status of the net.ipv4.icmp_ignore_bogus_error_responses kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.icmp_ignore_bogus_error_responses = 1 |
Ignoring bogus ICMP error responses reduces log size, although some activity would not be logged. |
| R12 | Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router,
which can be used to bypass network security measures. This requirement
applies only to the forwarding of source-routerd traffic, such as when IPv4
forwarding is enabled and the system is functioning as a router.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
| R12 | Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.default.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.accept_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages modify the
host's route table and are unauthenticated. An illicit ICMP redirect
message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required. |
| R12 | Disable Kernel Parameter for Accepting Source-Routed Packets on IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router,
which can be used to bypass network security measures.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router. |
| R12 | Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.send_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.send_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.send_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages contain information
from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers. |
| R12 | Disable Kernel Parameter for Accepting Secure ICMP Redirects on all IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.secure_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.secure_redirects = 0 |
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required. |
| R12 | Configure Sending and Accepting Shared Media Redirects by Default |
To set the runtime status of the net.ipv4.conf.default.shared_media kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.shared_media=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.shared_media = 0 |
This setting should be aligned with net.ipv4.conf.default.secure_redirects because it overrides it. If shared_media is enabled for an interface secure_redirects will be enabled too. |
| R12 | Harden the operation of the BPF just-in-time compiler |
To set the runtime status of the net.core.bpf_jit_harden kernel parameter, run the following command: $ sudo sysctl -w net.core.bpf_jit_harden=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.core.bpf_jit_harden = 2 |
When hardened, the extended Berkeley Packet Filter just-in-time compiler will randomize any kernel addresses in the BPF programs and maps, and will not expose the JIT addresses in /proc/kallsyms. |
| R12 | Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.send_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.send_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.send_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages contain information
from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers. |
| R12 | Configure ARP filtering for All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.arp_filter kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.arp_filter=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.arp_filter = 0 |
Prevents the Linux Kernel from handling the ARP table globally. By default, the kernel may respond to an ARP request from a certain interface with information from another interface. |
| R12 | Prevent Routing External Traffic to Local Loopback on All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.route_localnet kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.route_localnet=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.route_localnet = 0 |
Refuse the routing of packets whose source or destination address is the local loopback. This prohibits the use of network 127/8 for local routing purposes. Enabling route_localnet can expose applications listening on localhost to external traffic. |
| R12 | Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces by Default |
To set the runtime status of the net.ipv4.conf.default.rp_filter kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.rp_filter=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.rp_filter = 1 |
Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks. |
| R12 | Configure Kernel Parameter for Accepting Secure Redirects By Default |
To set the runtime status of the net.ipv4.conf.default.secure_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.default.secure_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.default.secure_redirects = 0 |
Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required. |
| R12 | Set Kernel Parameter to Increase Local Port Range |
To set the runtime status of the net.ipv4.ip_local_port_range kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.ip_local_port_range=32768 65535To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.ip_local_port_range = 32768 65535 |
This setting defines the local port range that is used by TCP and UDP to choose the local port. The first number is the first, the second the last local port number. |
| R12 | Drop Gratuitious ARP frames on All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.drop_gratuitous_arp kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.drop_gratuitous_arp=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.drop_gratuitous_arp = 1 |
Drop Gratuitous ARP frames to prevent ARP poisoning. |
| R12 | Disable Kernel Parameter for IP Forwarding on IPv4 Interfaces |
To set the runtime status of the net.ipv4.ip_forward kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.ip_forward=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.ip_forward = 0 |
Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this capability is used when not required, system network information may be unnecessarily transmitted across the network. |
| R12 | Disable Accepting ICMP Redirects for All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.accept_redirects = 0 |
ICMP redirect messages are used by routers to inform hosts that a more
direct route exists for a particular destination. These messages modify the
host's route table and are unauthenticated. An illicit ICMP redirect
message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required." |
| R12 | Configure Response Mode of ARP Requests for All IPv4 Interfaces |
To set the runtime status of the net.ipv4.conf.all.arp_ignore kernel parameter, run the following command: $ sudo sysctl -w net.ipv4.conf.all.arp_ignore=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv4.conf.all.arp_ignore = 0 |
Avoids ARP Flux on system that have more than one interface on the same subnet. |
| R13 | Configure Accepting Router Preference in Router Advertisements on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.accept_ra_rtr_pref kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_ra_rtr_pref=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_ra_rtr_pref = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Disable Accepting ICMP Redirects for All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_redirects = 0 |
An illicit ICMP redirect message could result in a man-in-the-middle attack. |
| R13 | Configure Accepting Prefix Information in Router Advertisements on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.accept_ra_pinfo kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_ra_pinfo=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_ra_pinfo = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Configure Accepting Prefix Information in Router Advertisements on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_ra_pinfo kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_ra_pinfo=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_ra_pinfo = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers
forward the packet along a different path than configured on the router, which can
be used to bypass network security measures. This requirement applies only to the
forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and
the system is functioning as a router.
Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
| R13 | Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.default.accept_redirects kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_redirects=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_redirects = 0 |
An illicit ICMP redirect message could result in a man-in-the-middle attack. |
| R13 | Configure Accepting Router Preference in Router Advertisements on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_ra_rtr_pref kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_ra_rtr_pref=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_ra_rtr_pref = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Disable Kernel Parameter for Accepting Source-Routed Packets on IPv6 Interfaces by Default |
To set the runtime status of the net.ipv6.conf.default.accept_source_route kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_source_route=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_source_route = 0 |
Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router. Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required. |
| R13 | Configure Accepting Default Router in Router Advertisements on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.accept_ra_defrtr kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.accept_ra_defrtr=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.accept_ra_defrtr = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Configure Auto Configuration on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.autoconf kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.autoconf=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.autoconf = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Configure Maximum Number of Autoconfigured Addresses on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.max_addresses kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.max_addresses=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.max_addresses = 1 |
The number of global unicast IPv6 addresses for each interface should be limited exactly to the number of statically configured addresses. |
| R13 | Configure Auto Configuration on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.autoconf kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.autoconf=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.autoconf = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Configure Maximum Number of Autoconfigured Addresses on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.max_addresses kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.max_addresses=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.max_addresses = 1 |
The number of global unicast IPv6 addresses for each interface should be limited exactly to the number of statically configured addresses. |
| R13 | Configure Denying Router Solicitations on All IPv6 Interfaces |
To set the runtime status of the net.ipv6.conf.all.router_solicitations kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.all.router_solicitations=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.all.router_solicitations = 0 |
To prevent discovery of the system by other systems, router solicitation requests should be denied. |
| R13 | Configure Accepting Default Router in Router Advertisements on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.accept_ra_defrtr kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.accept_ra_defrtr=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.accept_ra_defrtr = 0 |
An illicit router advertisement message could result in a man-in-the-middle attack. |
| R13 | Configure Denying Router Solicitations on All IPv6 Interfaces By Default |
To set the runtime status of the net.ipv6.conf.default.router_solicitations kernel parameter, run the following command: $ sudo sysctl -w net.ipv6.conf.default.router_solicitations=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: net.ipv6.conf.default.router_solicitations = 0 |
To prevent discovery of the system by other systems, router solicitation requests should be denied. |
| R14 | Enable Kernel Parameter to Enforce DAC on FIFOs |
To set the runtime status of the fs.protected_fifos kernel parameter, run the following command: $ sudo sysctl -w fs.protected_fifos=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.protected_fifos = 2 |
This parameter is available since Linux Kernel 4.19 and allows to prohibit opening FIFOs that are not owned by the user in world and group writeable sticky directories. It avoids unintentional writes to an attacker-controlled FIFO where a program expects to create the regular file. |
| R14 | Enable Kernel Parameter to Enforce DAC on Symlinks |
To set the runtime status of the fs.protected_symlinks kernel parameter, run the following command: $ sudo sysctl -w fs.protected_symlinks=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.protected_symlinks = 1 |
By enabling this kernel parameter, symbolic links are permitted to be followed only when outside a sticky world-writable directory, or when the UID of the link and follower match, or when the directory owner matches the symlink's owner. Disallowing such symlinks helps mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). |
| R14 | Enable Kernel Parameter to Enforce DAC on Hardlinks |
To set the runtime status of the fs.protected_hardlinks kernel parameter, run the following command: $ sudo sysctl -w fs.protected_hardlinks=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.protected_hardlinks = 1 |
By enabling this kernel parameter, users can no longer create soft or hard links to files which they do not own. Disallowing such hardlinks mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). |
| R14 | Enable Kernel Parameter to Enforce DAC on Regular files |
To set the runtime status of the fs.protected_regular kernel parameter, run the following command: $ sudo sysctl -w fs.protected_regular=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.protected_regular = 2 |
This parameter is available since Linux Kernel 4.19 and allows to prohibit opening "regular" files that are not owned by the user in world and group writeable sticky directories. It avoids writes to an attacker-controlled regular file, for example, when a program expects to create the regular file. |
| R14 | Disable Core Dumps for SUID programs |
To set the runtime status of the fs.suid_dumpable kernel parameter, run the following command: $ sudo sysctl -w fs.suid_dumpable=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: fs.suid_dumpable = 0 |
The core dump of a setuid program is more likely to contain sensitive data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data. |
| R15 | Do not allow usercopy whitelist violations to fallback to object size | This is a temporary option that allows missing usercopy whitelists to be discovered via a WARN() to the kernel log, instead of rejecting the copy, falling back to non-whitelisted hardened usercopy that checks the slab allocation size instead of the whitelist size. This configuration is available from kernel 4.16. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_HARDENED_USERCOPY_FALLBACK, run the following command: grep CONFIG_HARDENED_USERCOPY_FALLBACK /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | This config prevents entire classes of heap overflow exploits and similar kernel memory exposures. |
| R15 | Detect stack corruption on calls to schedule() | This option checks for a stack overrun on calls to schedule(). If the stack end location is found to be overwritten always panic as the content of the corrupted region can no longer be trusted. This configuration is available from kernel 3.18. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SCHED_STACK_END_CHECK, run the following command: grep CONFIG_SCHED_STACK_END_CHECK /boot/config-* For each kernel installed, a line with value "y" should be returned. | This ensures no erroneous behaviour occurs which could result in data corruption or a sporadic crash at a later stage once the region is examined. |
| R15 | Disable support for /proc/kkcore | Provides a virtual ELF core file of the live kernel. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PROC_KCORE, run the following command: grep CONFIG_PROC_KCORE /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | This feature exposes the memory to the userspace and can assist an attacker in discovering attack vectors. |
| R15 | Disable vsyscall mapping | This config disables the vsyscall mapping at all. Attempts to use the vsyscalls will be reported to dmesg, so that either old or malicious userspace programs can be identified. This configuration is available from kernel 4.4. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_LEGACY_VSYSCALL_NONE, run the following command: grep CONFIG_LEGACY_VSYSCALL_NONE /boot/config-* For each kernel installed, a line with value "y" should be returned. | This will eliminate any risk of ASLR bypass due to the vsyscall fixed address mapping. |
| R15 | Disable the 32-bit vDSO | Certain buggy versions of glibc (2.3.3) will crash if they are presented with a 32-bit vDSO that is not mapped at the address indicated in its segment table. Setting CONFIG_COMPAT_VDSO to y turns off the 32-bit VDSO and works aroud the glibc bug. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_COMPAT_VDSO, run the following command: grep CONFIG_COMPAT_VDSO /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Enabling VDSO compatibility hurts performance and disables ASLR. |
| R15 | Disable x86 vsyscall emulation | Disabling it is roughly equivalent to booting with vsyscall=none, except that it will also disable the helpful warning if a program tries to use a vsyscall. With this option set to N, offending programs will just segfault, citing addresses of the form 0xffffffffff600?00. This configuration is available from kernel 3.19. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_X86_VSYSCALL_EMULATION, run the following command: grep CONFIG_X86_VSYSCALL_EMULATION /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | The vsyscall table is no longer required and is a potential source of ROP gadgets. |
| R15 | Disable vsyscall emulation | The kernel traps and emulates calls into the fixed vsyscall address mapping. This configuration is available from kernel 5.3, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_LEGACY_VSYSCALL_EMULATE, run the following command: grep CONFIG_LEGACY_VSYSCALL_EMULATE /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | The mapping is non-executable, but it still contains known contents, which could be used in certain rare security vulnerability exploits. |
| R15 | Harden memory copies between kernel and userspace | This option checks for obviously wrong memory regions when copying memory to/from the kernel (via copy_to_user() and copy_from_user() functions) by rejecting memory ranges that are larger than the specified heap object, span multiple separately allocated pages, are not on the process stack, or are part of the kernel text. This configuration is available from kernel 4.8, and may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_HARDENED_USERCOPY, run the following command: grep CONFIG_HARDENED_USERCOPY /boot/config-* For each kernel installed, a line with value "y" should be returned. | This config prevents entire classes of heap overflow exploits and similar kernel memory exposures. |
| R15 | Strong Stack Protector | This features adds canary logic protection to more kinds of vulnerable functions than CONFIG_STACKPROTECTOR, but not to all functions so that performance is not severily impacted. This configuration is available from kernel 4.18. This config requires gcc version 4.9 or above, or a distribution gcc with the feature backported ("-fstack-protector-strong"). The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_STACKPROTECTOR_STRONG, run the following command: grep CONFIG_STACKPROTECTOR_STRONG /boot/config-* For each kernel installed, a line with value "y" should be returned. | This provides a mechanism that protects more vulnerable functions than CONFIG_STACKPROTECTOR, balancing between security and performance. |
| R15 | Harden common str/mem functions against buffer overflows | Detect overflows of buffers in common string and memory functions where the compiler can determine and validate the buffer sizes. This configuration is available from kernel 4.13, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_FORTIFY_SOURCE, run the following command: grep CONFIG_FORTIFY_SOURCE /boot/config-* For each kernel installed, a line with value "y" should be returned. | This features helps reduce likelihood of memory corruption of kernel structures. |
| R15 | Disable kernel debugfs | debugfs is a virtual file system that kernel developers use to put debugging files into. Enable this option to be able to read and write to these files. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_FS, run the following command: grep CONFIG_DEBUG_FS /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | To reduce the attack surface, this file system should be disabled if not in use. |
| R15 | User a virtually-mapped stack | Enable this to use virtually-mapped kernel stacks with guard pages. This configuration is available from kernel 4.9. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_VMAP_STACK, run the following command: grep CONFIG_VMAP_STACK /boot/config-* For each kernel installed, a line with value "y" should be returned. | This causes kernel stack overflows to be caught immediately rather than causing difficult-to-diagnose corruption. |
| R15 | Warn on W+X mappings found at boot | Generate a warning if any W+X mappings are found at boot. This configuration is available from kernel 5.8. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_WX, run the following command: grep CONFIG_DEBUG_WX /boot/config-* For each kernel installed, a line with value "y" should be returned. | This is useful for discovering cases where the kernel is leaving W+X mappings after applying NX, as such mappings are a security risk. Note that even if the check fails, your kernel is possibly still fine, as W+X mappings are not a security hole in themselves, what they do is that they make the exploitation of other unfixed kernel bugs easier. |
| R15 | Make the kernel text and rodata read-only | When set, kernel text and rodata memory will be made read-only, and non-text memory will be made non-executable. This configuration is available from kernel 4.11. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_STRICT_KERNEL_RWX, run the following command: grep CONFIG_STRICT_KERNEL_RWX /boot/config-* For each kernel installed, a line with value "y" should be returned. | This provides protection against certain security exploits (e.g. executing the heap or modifying text) |
| R15 | Do not allow ACPI methods to be inserted/replaced at run time | This debug facility allows ACPI AML methods to be inserted and/or replaced without rebooting the system. This configuration is available from kernel 3.0. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_ACPI_CUSTOM_METHOD, run the following command: grep CONFIG_ACPI_CUSTOM_METHOD /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Enabling this feature allows arbitrary kernel memory to be written to by root (uid=0) users, allowing them to bypass certain security measures |
| R15 | Disable /dev/kmem virtual device support | Disable support for the /dev/kmem device. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEVKMEM, run the following command: grep CONFIG_DEVKMEM /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | The /dev/kmem device is rarely used, but can be used for certain kind of kernel debugging operations. |
| R15 | Avoid speculative indirect branches in kernel | Compile kernel with the retpoline compiler options to guard against kernel-to-user data leaks by avoiding speculative indirect branches. Requires a compiler with -mindirect-branch=thunk-extern support for full protection. The kernel may run slower. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_RETPOLINE, run the following command: grep CONFIG_RETPOLINE /boot/config-* For each kernel installed, a line with value "y" should be returned. | This is required to enable protection against Spectre v2. |
| R15 | Restrict unprivileged access to the kernel syslog | Enforce restrictions on unprivileged users reading the kernel syslog via dmesg(8). The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECURITY_DMESG_RESTRICT, run the following command: grep CONFIG_SECURITY_DMESG_RESTRICT /boot/config-* For each kernel installed, a line with value "y" should be returned. | Prevents unprivileged users from retrieving kernel addresses with dmesg. |
| R15 | Disable vsyscall emulate execution only | The kernel traps and emulates calls into the fixed vsyscall address mapping and does not allow reads. This configuration is available from kernel 5.3. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_LEGACY_VSYSCALL_XONLY, run the following command: grep CONFIG_LEGACY_VSYSCALL_XONLY /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Disabling this mitigates certain uses of the vsyscall area as an ASLR-bypassing buffer. |
| R15 | Stack Protector buffer overlow detection | This feature puts, at the beginning of functions, a canary value on the stack just before the return address, and validates the value just before actually returning. This configuration is available from kernel 4.18. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_STACKPROTECTOR, run the following command: grep CONFIG_STACKPROTECTOR /boot/config-* For each kernel installed, a line with value "y" should be returned. | This halts the program when a stack overflow is detected, potentially reducing the impact of exploits. |
| R15 | Perform full reference count validation | Enabling this switches the refcounting infrastructure from a fast unchecked atomic_t implementation to a fully state checked implementation, which can have a slight impact in performance. This configuration is available from kernel 4.13, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_REFCOUNT_FULL, run the following command: grep CONFIG_REFCOUNT_FULL /boot/config-* For each kernel installed, a line with value "y" should be returned. | Refcounting provides protections against various use-after-free conditions that can be used in security flaw exploits. |
| R16 | Enable checks on notifier call chains | Enable this to turn on sanity checking for notifier call chains. This is most useful for kernel developers to make sure that modules properly unregister themselves from notifier chains. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_NOTIFIERS, run the following command: grep CONFIG_DEBUG_NOTIFIERS /boot/config-* For each kernel installed, a line with value "y" should be returned. | This provides validation of notifier chains, it checks whether the notifiers are from the kernel or a module that is still loaded prior to being invoked. |
| R16 | Trigger a kernel BUG when data corruption is detected | This option makes the kernel BUG when it encounters data corruption in kernel memory structures when they get checked for validity. This configuration is available from kernel 4.10. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_BUG_ON_DATA_CORRUPTION, run the following command: grep CONFIG_BUG_ON_DATA_CORRUPTION /boot/config-* For each kernel installed, a line with value "y" should be returned. | This helps detect data corruptions early and stop with a BUG() error message. |
| R16 | Enable checks on credential management | Enable this to turn on some debug checking for credential management. The additional code keeps track of the number of pointers from task_structs to any given cred struct, and checks to see that this number never exceeds the usage count of the cred struct. Furthermore, if SELinux is enabled, this also checks that the security pointer in the cred struct is never seen to be invalid. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_CREDENTIALS, run the following command: grep CONFIG_DEBUG_CREDENTIALS /boot/config-* For each kernel installed, a line with value "y" should be returned. | This adds sanity checks and validations to credential data structures. |
| R16 | Enable checks on scatter-gather (SG) table operations | Scatter-gather tables are mechanism used for high performance I/O on DMA devices. Enable this to turn on checks on scatter-gather tables. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_SG, run the following command: grep CONFIG_DEBUG_SG /boot/config-* For each kernel installed, a line with value "y" should be returned. | This can help find problems with drivers that do not properly initialize their SG tables. |
| R16 | Enable checks on linked list manipulation | Enable this to turn on extended checks in the linked-list walking routines. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEBUG_LIST, run the following command: grep CONFIG_DEBUG_LIST /boot/config-* For each kernel installed, a line with value "y" should be returned. | This add sanity checks to manipulation of linked lists structures in the kernel and may prevent exploits such as CVE-2017-1661, where a race condition and simultaneos operations caused a list to corrupt. |
| R17 | Randomize slab freelist | Randomizes the freelist order used on creating new pages. This configuration is available from kernel 5.9, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SLAB_FREELIST_RANDOM, run the following command: grep CONFIG_SLAB_FREELIST_RANDOM /boot/config-* For each kernel installed, a line with value "y" should be returned. | This security feature reduces the predictability of the kernel slab allocator against heap overflows. |
| R17 | Enable poison of pages after freeing | Fill the pages with poison patterns after free_pages() and verify the patterns before alloc_pages. This does have a potential performance impact if enabled with the "page_poison=1" kernel boot option. This configuration is available from kernel 4.6. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PAGE_POISONING, run the following command: grep CONFIG_PAGE_POISONING /boot/config-* For each kernel installed, a line with value "y" should be returned. | The filling of the memory helps reduce the risk of information leaks from freed data. |
| R17 | Disable compatibility with brk() | Enabling compatiliby with brk() allows legacy binaries to run (i.e. those linked against libc5). But this compatibility comes at the cost of not being able to randomize the heap placement (ASLR). Unless legacy binaries need to run on the system, set CONFIG_COMPAT_BRK to "n". The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_COMPAT_BRK, run the following command: grep CONFIG_COMPAT_BRK /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Enabling compatibility with brk() disables support for ASLR. |
| R17 | Disallow merge of slab caches | For reduced kernel memory fragmentation, slab caches can be merged when they share the same size and other characteristics. This carries a risk of kernel heap overflows being able to overwrite objects from merged caches (and more easily control cache layout), which makes such heap attacks easier to exploit by attackers. This configuration is available from kernel 4.13. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SLAB_MERGE_DEFAULT, run the following command: grep CONFIG_SLAB_MERGE_DEFAULT /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Disabling the merge of slabs of similar sizes prevents the kernel from merging a seemingly useless but vulnerable slab with a useful and valuable slab. This increase the risk that a heap overflow could overwrite objects from merged caches, with unmerged caches the heap overflow would only affect the objects in the same cache. Overall, this reduces the kernel attack surface area by isolating slabs from each other. |
| R17 | Harden slab freelist metadata | This feature protects integrity of the allocator's metadata. This configuration is available from kernel 4.14. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SLAB_FREELIST_HARDENED, run the following command: grep CONFIG_SLAB_FREELIST_HARDENED /boot/config-* For each kernel installed, a line with value "y" should be returned. | Many kernel heap attacks try to target slab cache metadata and other infrastructure. This options makes minor performance sacrifices to harden the kernel slab allocator against common freelist exploit methods. |
| R17 | Enable SLUB debugging support | SLUB has extensive debug support features and this allows the allocator validation checking to be enabled. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SLUB_DEBUG, run the following command: grep CONFIG_SLUB_DEBUG /boot/config-* For each kernel installed, a line with value "y" should be returned. | This activates the checking of the memory allocator structures and resets to zero the zones allocated when they are released. |
| R17 | Enable poison without sanity check | Skip the sanity checking on alloc, only fill the pages with poison on free. This reduces some of the overhead of the poisoning feature. This configuration is available from kernel 4.6. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PAGE_POISONING_NO_SANITY, run the following command: grep CONFIG_PAGE_POISONING_NO_SANITY /boot/config-* For each kernel installed, a line with value "y" should be returned. | This configuration helps alleviates the performance impact of poisonining. |
| R17 | Use zero for poisoning instead of debugging value | Instead of using the existing poison value, fill the pages with zeros. This makes it harder to detect when errors are occurring due to sanitization but the zeroing at free means that it is no longer necessary to write zeros when GFP_ZERO is used on allocation. This configuration is available from kernel 4.19. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PAGE_POISONING_ZERO, run the following command: grep CONFIG_PAGE_POISONING_ZERO /boot/config-* For each kernel installed, a line with value "y" should be returned. | This configuration helps alleviates the performance impact of poisonining. |
| R18 | Sign kernel modules with SHA-512 | This configures the kernel to build and sign modules using SHA512 as the hash function. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_SHA512, run the following command: grep CONFIG_MODULE_SIG_SHA512 /boot/config-* For each kernel installed, a line with value "y" should be returned. | Use of strong hash function is important to secure the module against counterfeit signatures. |
| R18 | Specify the hash to use when signing modules | This configures the kernel to build and sign modules using sha512 as the hash function. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_HASH, run the following command: grep CONFIG_MODULE_SIG_HASH /boot/config-* For each kernel installed, a line with value "sha512" should be returned. | Use of strong hash function is important to secure the module against counterfeit signatures. |
| R18 | Make the module text and rodata read-only | When set, module text and rodata memory will be made read-only, and non-text memory will be made non-executable. This configuration is available from kernel 4.11. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_STRICT_MODULE_RWX, run the following command: grep CONFIG_STRICT_MODULE_RWX /boot/config-* For each kernel installed, a line with value "y" should be returned. | This provides protection against certain security exploits (e.g. executing the heap or modifying text) |
| R18 | Enable module signature verification | Check modules for valid signatures upon load. Note that this option adds the OpenSSL development packages as a kernel build dependency so that the signing tool can use its crypto library. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG, run the following command: grep CONFIG_MODULE_SIG /boot/config-* For each kernel installed, a line with value "y" should be returned. | Loaded modules must be signed. |
| R18 | Require modules to be validly signed | Reject unsigned modules or signed modules with an unknown key. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_FORCE, run the following command: grep CONFIG_MODULE_SIG_FORCE /boot/config-* For each kernel installed, a line with value "y" should be returned. | Prevent loading modules that are unsigned or signed with an unknown key. |
| R18 | Enable automatic signing of all modules | Sign all modules during make modules_install. Without this option, modules must be signed manually, using the scripts/sign-file tool. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_ALL, run the following command: grep CONFIG_MODULE_SIG_ALL /boot/config-* For each kernel installed, a line with value "y" should be returned. | This ensures the modules are signed during install process. |
| R18 | Specify module signing key to use | Setting this option to something other than its default of certs/signing_key.pem will disable the autogeneration of signing keys and allow the kernel modules to be signed with a key of your choosing. The string provided should identify a file containing both a private key and its corresponding X.509 certificate in PEM form, or — on systems where the OpenSSL ENGINE_pkcs11 is functional — a PKCS#11 URI as defined by RFC7512. In the latter case, the PKCS#11 URI should reference both a certificate and a private key. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_KEY, run the following command: grep CONFIG_MODULE_SIG_KEY /boot/config-* For each kernel installed, a line with value "certs/signing_key.pem" should be returned. | A key and certificate is required to sign the built modules. |
| R19 | Kernel panic oops | Enable the kernel to panic when it oopses. This has the same effect as setting oops=panic on the kernel command line. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PANIC_ON_OOPS, run the following command: grep CONFIG_PANIC_ON_OOPS /boot/config-* For each kernel installed, a line with value "y" should be returned. | This feature ensures that the kernel does not do anything erroneous after an oops which could result in data corruption or other issues. |
| R19 | Enable support for BUG() | Disabling this option eliminates support for BUG and WARN, reducing the size of your kernel image and potentially quietly ignoring numerous fatal conditions. You should only consider disabling this option for embedded systems with no facilities for reporting errors. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_BUG, run the following command: grep CONFIG_BUG /boot/config-* For each kernel installed, a line with value "y" should be returned. | Not setting this variable may hide a number of critical errors. |
| R19 | Kernel panic timeout | Set the timeout value (in seconds) until a reboot occurs when the kernel panics. A timeout of 0 configures the system to wait forever. With a timeout value greater than 0, the system will wait the specified amount of seconds before rebooting. While a timeout value less than 0 makes the system reboot immediately. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PANIC_TIMEOUT, run the following command: grep CONFIG_PANIC_TIMEOUT /boot/config-* For each kernel installed, a line with value "0" should be returned. | This is required to enable protection against Spectre v2. |
| R20 | Enable use of Berkeley Packet Filter with seccomp | Enable tasks to build secure computing environments defined in terms of Berkeley Packet Filter programs which implement task-defined system call filtering polices. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECCOMP_FILTER, run the following command: grep CONFIG_SECCOMP_FILTER /boot/config-* For each kernel installed, a line with value "y" should be returned. | Use of BPF filters allows for expressive filtering of system calls using a filter program language with a long history of being exposed to userland. |
| R20 | Enable seccomp to safely compute untrusted bytecode | This kernel feature is useful for number crunching applications that may need to compute untrusted bytecode during their execution. By using pipes or other transports made available to the process as file descriptors supporting the read/write syscalls, it's possible to isolate those applications in their own address space using seccomp. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECCOMP, run the following command: grep CONFIG_SECCOMP /boot/config-* For each kernel installed, a line with value "y" should be returned. | seccomp enables the ability to filter system calls made by an application, effectively isolating the system's resources from it. |
| R20 | Disable mutable hooks | Ensure kernel structures associated with LSMs are always mapped as read-only after system boot. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECURITY_WRITABLE_HOOKS, run the following command: grep CONFIG_SECURITY_WRITABLE_HOOKS /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | If CONFIG_SECURITY_WRITABLE_HOOKS is enabled, then hooks can be loaded at runtime and being able to manipulate hooks is a way to bypass all LSMs. |
| R20 | Enable different security models | This allows you to choose different security modules to be configured into your kernel. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECURITY, run the following command: grep CONFIG_SECURITY /boot/config-* For each kernel installed, a line with value "y" should be returned. | This is enables kernel security primitives required by the LSM framework. |
| R20 | Enable Yama support | This enables support for LSM module Yama, which extends DAC support with additional system-wide security settings beyond regular Linux discretionary access controls. The module will limit the use of the system call ptrace(). The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SECURITY_YAMA, run the following command: grep CONFIG_SECURITY_YAMA /boot/config-* For each kernel installed, a line with value "y" should be returned. | Unrestricted usage of ptrace allows compromised binaries to run ptrace on another processes of the user. |
| R21 | zero-init everything passed by reference | Zero-initialize any stack variables that may be passed by reference and had not already been explicitly initialized. This configuration is available from kernel 4.14, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL, run the following command: grep CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL /boot/config-* For each kernel installed, a line with value "y" should be returned. | This eliminates all classes of uninitialized stack variable exploits and information exposures. |
| R21 | Generate some entropy during boot and runtime | Instrument some kernel code to extract some entropy from both original and artificially created program state. This will help especially embedded systems where there is little 'natural' source of entropy normally. This configuration is available from kernel 4.9, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_GCC_PLUGIN_LATENT_ENTROPY, run the following command: grep CONFIG_GCC_PLUGIN_LATENT_ENTROPY /boot/config-* For each kernel installed, a line with value "y" should be returned. | This helps generate entropy during startup and is particularly relevant for devices with inappropriate entropy sources. |
| R21 | Randomize layout of sensitive kernel structures | Randomize at compile-time the layouts of structures that are entirely function pointers (and have not been manually annotated with __no_randomize_layout), or structures that have been explicitly marked with __randomize_layout. This configuration is available from kernel 4.13, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_GCC_PLUGIN_RANDSTRUCT, run the following command: grep CONFIG_GCC_PLUGIN_RANDSTRUCT /boot/config-* For each kernel installed, a line with value "y" should be returned. | Randomizing the layout of kernel data structures make it more difficult for an attacker to know the location of sensitive data. |
| R21 | Force initialization of variables containing userspace addresses | While the kernel is built with warnings enabled for any missed stack variable initializations, this warning is silenced for anything passed by reference to another function, under the occasionally misguided assumption that the function will do the initialization. As this regularly leads to exploitable flaws, this plugin is available to identify and zero-initialize such variables, depending on the chosen level of coverage. This configuration is available from kernel 4.11, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_GCC_PLUGIN_STRUCTLEAK, run the following command: grep CONFIG_GCC_PLUGIN_STRUCTLEAK /boot/config-* For each kernel installed, a line with value "y" should be returned. | Initializing structures from userspace can prevent some classes of information exposure. |
| R21 | Poison kernel stack before returning from syscalls | This option makes the kernel erase the kernel stack before returning from system calls. This has the effect of leaving the stack initialized to the poison value, which both reduces the lifetime of any sensitive stack contents and reduces potential for uninitialized stack variable exploits or information exposures (it does not cover functions reaching the same stack depth as prior functions during the same syscall). This configuration is available from kernel 4.20, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_GCC_PLUGIN_STACKLEAK, run the following command: grep CONFIG_GCC_PLUGIN_STACKLEAK /boot/config-* For each kernel installed, a line with value "y" should be returned. | This blocks most uninitialized stack variable attacks, with the performance impact being driven by the depth of the stack usage, rather than the function calling complexity. |
| R22 | Enable TCP/IP syncookie support | Normal TCP/IP networking is open to an attack known as SYN flooding. It is denial-of-service attack that prevents legitimate remote users from being able to connect to your computer during an ongoing attack. When enabled the TCP/IP stack will use a cryptographic challenge protocol known as SYN cookies to enable legitimate users to continue to connect, even when your machine is under attack. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_SYN_COOKIES, run the following command: grep CONFIG_SYN_COOKIES /boot/config-* For each kernel installed, a line with value "y" should be returned. | SYN cookies provide protection against SYN flooding attacks. |
| R23 | Disable kernel support for MISC binaries | Enabling CONFIG_BINFMT_MISC makes it possible to plug wrapper-driven binary formats into the kernel. This is specially useful for programs that need an interpreter to run like Java, Python and DOS emulators. Once you have registered such a binary class with the kernel, you can start one of those programs simply by typing in its name at a shell prompt. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_BINFMT_MISC, run the following command: grep CONFIG_BINFMT_MISC /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | This disables arbitrary binary format support and helps reduce attack surface. |
| R23 | Disable legacy (BSD) PTY support | Disable the Linux traditional BSD-like terminal names /dev/ptyxx for masters and /dev/ttyxx for slaves of pseudo terminals, and use only the modern ptys (devpts) interface. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_LEGACY_PTYS, run the following command: grep CONFIG_LEGACY_PTYS /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | The legacy scheme has a number of security problems. |
| R23 | Disable kexec system call | kexec is a system call that implements the ability to shutdown your current kernel, and to start another kernel. It is like a reboot but it is independent of the system firmware. And like a reboot you can start any kernel with it, not just Linux. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_KEXEC, run the following command: grep CONFIG_KEXEC /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Prohibits the execution of a new kernel image after reboot. |
| R23 | Disable hibernation | Enable the suspend to disk (STD) functionality, which is usually called "hibernation" in user interfaces. STD checkpoints the system and powers it off; and restores that checkpoint on reboot. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_HIBERNATION, run the following command: grep CONFIG_HIBERNATION /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Suspending to disk allows one to replace the running kernel. |
| R25 R27 |
Configure Low Address Space To Protect From User Allocation | This is the portion of low virtual memory which should be protected from userspace allocation. This configuration is available from kernel 3.14, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_DEFAULT_MMAP_MIN_ADDR, run the following command: grep CONFIG_DEFAULT_MMAP_MIN_ADDR /boot/config-* For each kernel installed, a line with value should be returned. If the system architecture is x86_64, the value should be 65536. If the system architecture is aarch64, the value should be 32768. | Keeping a user from writing to low pages can help reduce the impact of kernel NULL pointer bugs. |
| R25 | Disable the LDT (local descriptor table) | Linux can allow user programs to install a per-process x86 Local Descriptor Table (LDT) using the modify_ldt(2) system call. This is required to run 16-bit or segmented code such as DOSEMU or some Wine programs. It is also used by some very old threading libraries. This configuration is available from kernel 4.3, but may be available if backported by distros. Disable LDT if 16-bit program emulation is not necessary. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODIFY_LDT_SYSCALL, run the following command: grep CONFIG_MODIFY_LDT_SYSCALL /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Disabling support for unnecessary code reduces attack surface. |
| R25 | Disable IA32 emulation | Disables support for legacy 32-bit programs under a 64-bit kernel. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_IA32_EMULATION, run the following command: grep CONFIG_IA32_EMULATION /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned. | Disabling 32-bit backwards compatibility helps reduce the attack surface. |
| R25 R27 |
Randomize the address of the kernel image (KASLR) | In support of Kernel Address Space Layout Randomization (KASLR), this randomizes the physical address at which the kernel image is decompressed and the virtual address where the kernel image is mapped. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_RANDOMIZE_BASE, run the following command: grep CONFIG_RANDOMIZE_BASE /boot/config-* For each kernel installed, a line with value "y" should be returned. | An unpredictable kernel address makes it more difficult to succeed with exploits that rely on knowledge of the location of kernel code internals. |
| R25 | Remove the kernel mapping in user mode | This feature reduces the number of hardware side channels by ensuring that the majority of kernel addresses are not mapped into userspace. This configuration is available from kernel 4.15, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_PAGE_TABLE_ISOLATION, run the following command: grep CONFIG_PAGE_TABLE_ISOLATION /boot/config-* For each kernel installed, a line with value "y" should be returned. | This is a countermeasure to the Meltdown attack. |
| R25 | Randomize the kernel memory sections | Randomizes the base virtual address of kernel memory sections (physical memory mapping, vmalloc & vmemmap). This configuration is available from kernel 4.8, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_RANDOMIZE_MEMORY, run the following command: grep CONFIG_RANDOMIZE_MEMORY /boot/config-* For each kernel installed, a line with value "y" should be returned. | This security feature makes exploits relying on predictable memory locations less reliable. |
| R27 | Unmap kernel when running in userspace (aka KAISER) | Speculation attacks against some high-performance processors can be used to bypass MMU permission checks and leak kernel data to userspace. This can be defended against by unmapping the kernel when running in userspace, mapping it back in on exception entry via a trampoline page in the vector table. This configuration is available from kernel 4.16, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_UNMAP_KERNEL_AT_EL0, run the following command: grep CONFIG_UNMAP_KERNEL_AT_EL0 /boot/config-* For each kernel installed, a line with value "y" should be returned. | This is a countermeasure to the Meltdown attack. |
| R27 | Emulate Privileged Access Never (PAN) | Enabling this option prevents the kernel from accessing user-space memory directly by pointing TTBR0_EL1 to a reserved zeroed area and reserved ASID. The user access routines restore the valid TTBR0_EL1 temporarily. This configuration is available from kernel 4.10, but may be available if backported by distros. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_ARM64_SW_TTBR0_PAN, run the following command: grep CONFIG_ARM64_SW_TTBR0_PAN /boot/config-* For each kernel installed, a line with value "y" should be returned. | The Privileged Access Never (PAN) is the ARM equivalent of the x86 Supervisor Mode Access Prevention (SMAP), and it prevents privileged acccess to user data unless explicitly enabled. |
| R28 | Add noexec Option to /var/tmp |
The noexec mount option can be used to prevent binaries
from being executed out of /var/tmp.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/tmp.
|
Allowing users to execute binaries from world-writable directories such as /var/tmp should never be necessary in normal operation and can expose the system to potential compromise. |
| R28 | Ensure /var/tmp Located On Separate Partition | The /var/tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. | The /var/tmp partition is used as temporary storage by many programs. Placing /var/tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it. |
| R28 | Add noexec Option to /boot |
The noexec mount option can be used to prevent binaries from being
executed out of /boot.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/boot.
|
The /boot partition contains the kernel and the bootloader. No binaries should be executed from this partition after the booting process finishes. |
| R28 | Add nosuid Option to /var/tmp |
The nosuid mount option can be used to prevent
execution of setuid programs in /var/tmp. The SUID and SGID permissions
should not be required in these world-writable directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/tmp.
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions. |
| R28 | Add nodev Option to Non-Root Local Partitions |
The nodev mount option prevents files from being interpreted as
character or block devices. Legitimate character and block devices should
exist only in the /dev directory on the root partition or within
chroot jails built for system services.
Add the nodev option to the fourth column of
/etc/fstab for the line which controls mounting of
any non-root local partitions.
|
The nodev mount option prevents files from being interpreted as character or block devices. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails, for which it is not advised to set nodev on these filesystems. |
| R28 | Add noexec Option to /var |
The noexec mount option can be used to prevent binaries from being
executed out of /var.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/var.
|
The /var directory contains variable system data such as logs, mails and caches. No binaries should be executed from this directory. |
| R28 | Add nosuid Option to /var/log |
The nosuid mount option can be used to prevent
execution of setuid programs in /var/log. The SUID and SGID permissions
should not be required in directories containing log files.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/log.
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from partitions designated for log files. |
| R28 | Add nosuid Option to /home |
The nosuid mount option can be used to prevent
execution of setuid programs in /home. The SUID and SGID permissions
should not be required in these user data directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/home.
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from user home directory partitions. |
| R28 | Ensure /var Located On Separate Partition | The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM. | Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages. |
| R28 | Add noexec Option to /var/log |
The noexec mount option can be used to prevent binaries
from being executed out of /var/log.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/var/log.
|
Allowing users to execute binaries from directories containing log files such as /var/log should never be necessary in normal operation and can expose the system to potential compromise. |
| R28 | Ensure /opt Located On Separate Partition | It is recommended that the /opt directory resides on a separate partition. | The /opt partition contains additional software, usually installed outside the packaging system. Putting this directory on a separate partition makes it easier to apply restrictions e.g. through the nosuid mount option. |
| R28 | Add nosuid Option to /tmp |
The nosuid mount option can be used to prevent
execution of setuid programs in /tmp. The SUID and SGID permissions
should not be required in these world-writable directories.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/tmp.
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions. |
| R28 | Ensure /var/log Located On Separate Partition |
System logs are stored in the /var/log directory.
Ensure that /var/log has its own partition or logical
volume at installation time, or migrate it using LVM.
|
Placing /var/log in its own partition enables better separation between log files and other files in /var/. |
| R28 | Add noexec Option to /home |
The noexec mount option can be used to prevent binaries from being
executed out of /home.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/home.
|
The /home directory contains data of individual users. Binaries in this directory should not be considered as trusted and users should not be able to execute them. |
| R28 | Ensure /usr Located On Separate Partition | It is recommended that the /usr directory resides on a separate partition. | The /usr partition contains system software, utilities and files. Putting it on a separate partition allows limiting its size and applying restrictions through mount options. |
| R28 | Ensure /boot Located On Separate Partition | It is recommended that the /boot directory resides on a separate partition. This makes it easier to apply restrictions e.g. through the noexec mount option. Eventually, the /boot partition can be configured not to be mounted automatically with the noauto mount option. | The /boot partition contains the kernel and bootloader files. Access to this partition should be restricted. |
| R28 | Add nosuid Option to /srv |
The nosuid mount option can be used to prevent
execution of setuid programs in /srv. The SUID and SGID permissions
should not be required in this directory.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/srv.
|
The presence of SUID and SGID executables should be tightly controlled. The /srv directory contains files served by various network services such as FTP. Users should not be able to execute SUID or SGID binaries from this directory. |
| R28 | Ensure tmp.mount Unit Us Enabled | The /tmp directory is a world-writable directory used for temporary file storage. This directory is managed by systemd-tmpfiles. Ensure that the tmp.mount systemd unit is enabled. | The /tmp directory is used as temporary storage by many programs. Placing /tmp in a tmpfs filesystem enables the setting of more restrictive mount options, which can help protect programs which use it. The tmp.mount unit configures the tmpfs filesystem and ensures the /tmp directory is wiped during reboot. |
| R28 | Ensure /home Located On Separate Partition | If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. | Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage. |
| R28 | Add nosuid Option to /boot |
The nosuid mount option can be used to prevent
execution of setuid programs in /boot. The SUID and SGID permissions
should not be required on the boot partition.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/boot.
|
The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from boot partitions. |
| R28 | Ensure /srv Located On Separate Partition | If a file server (FTP, TFTP...) is hosted locally, create a separate partition for /srv at installation time (or migrate it later using LVM). If /srv will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. | Srv deserves files for local network file server such as FTP. Ensuring that /srv is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage. |
| R28 | Add noexec Option to /tmp |
The noexec mount option can be used to prevent binaries
from being executed out of /tmp.
Add the noexec option to the fourth column of
/etc/fstab for the line which controls mounting of
/tmp.
|
Allowing users to execute binaries from world-writable directories such as /tmp should never be necessary in normal operation and can expose the system to potential compromise. |
| R28 | Add nosuid Option to /opt |
The nosuid mount option can be used to prevent
execution of setuid programs in /opt. The SUID and SGID permissions
should not be required in this directory.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/opt.
|
The presence of SUID and SGID executables should be tightly controlled. The /opt directory contains additional software packages. Users should not be able to execute SUID or SGID binaries from this directory. |
| R28 | Add nosuid Option to /var |
The nosuid mount option can be used to prevent
execution of setuid programs in /var. The SUID and SGID permissions
should not be required for this directory.
Add the nosuid option to the fourth column of
/etc/fstab for the line which controls mounting of
/var.
|
The presence of SUID and SGID executables should be tightly controlled. |
| R29 | Verify the UEFI Boot Loader grub.cfg Permissions |
File permissions for /boot/efi/EFI/redhat/grub.cfg should be set to 700.
To properly set the permissions of /boot/efi/EFI/redhat/grub.cfg, run the command:
$ sudo chmod 700 /boot/efi/EFI/redhat/grub.cfg |
Proper permissions ensure that only the root user can modify important boot parameters. |
| R29 | Verify /boot/grub2/grub.cfg Group Ownership |
The file /boot/grub2/grub.cfg should
be group-owned by the root group to prevent
destruction or modification of the file.
To properly set the group owner of /boot/grub2/grub.cfg, run the command:
$ sudo chgrp root /boot/grub2/grub.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. |
| R29 | Verify /boot/efi/EFI/redhat/user.cfg Permissions |
File permissions for /boot/efi/EFI/redhat/user.cfg should be set to 600.
To properly set the permissions of /boot/efi/EFI/redhat/user.cfg, run the command:
$ sudo chmod 600 /boot/efi/EFI/redhat/user.cfg |
Proper permissions ensure that only the root user can read or modify important boot parameters. |
| R29 | Verify User Who Owns System.map Files |
The System.map files are symbol map files generated during the compilation of the Linux
kernel. They contain the mapping between kernel symbols and their corresponding memory
addresses. These files must be owned by root.
To properly set the owner of /boot/System.map*, run the command:
$ sudo chown root /boot/System.map* |
The purpose of System.map files is primarily for debugging and profiling the kernel. Unrestricted access to these files might disclose information useful to attackers and malicious software leading to more sophisticated exploitation. |
| R29 | Verify Group Who Owns System.map Files |
The System.map files are symbol map files generated during the compilation of the Linux
kernel. They contain the mapping between kernel symbols and their corresponding memory
addresses. These files must be group-owned by root.
To properly set the group owner of /boot/System.map*, run the command:
$ sudo chgrp root /boot/System.map* |
The purpose of System.map files is primarily for debugging and profiling the kernel. Unrestricted access to these files might disclose information useful to attackers and malicious software leading to more sophisticated exploitation. |
| R29 | Verify the UEFI Boot Loader grub.cfg User Ownership |
The file /boot/efi/EFI/redhat/grub.cfg should
be owned by the root user to prevent destruction
or modification of the file.
To properly set the owner of /boot/efi/EFI/redhat/grub.cfg, run the command:
$ sudo chown root /boot/efi/EFI/redhat/grub.cfg |
Only root should be able to modify important boot parameters. |
| R29 | Verify the UEFI Boot Loader grub.cfg Group Ownership |
The file /boot/efi/EFI/redhat/grub.cfg should
be group-owned by the root group to prevent
destruction or modification of the file.
To properly set the group owner of /boot/efi/EFI/redhat/grub.cfg, run the command:
$ sudo chgrp root /boot/efi/EFI/redhat/grub.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. |
| R29 | Verify /boot/efi/EFI/redhat/user.cfg Group Ownership |
The file /boot/efi/EFI/redhat/user.cfg should be group-owned by the
root group to prevent reading or modification of the file.
To properly set the group owner of /boot/efi/EFI/redhat/user.cfg, run the command:
$ sudo chgrp root /boot/efi/EFI/redhat/user.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
| R29 | Verify Permissions on System.map Files |
The System.map files are symbol map files generated during the compilation of the Linux
kernel. They contain the mapping between kernel symbols and their corresponding memory
addresses. In general, there is no need for non-root users to read these files.
To properly set the permissions of /boot/System.map*, run the command:
$ sudo chmod 0600 /boot/System.map* |
The purpose of System.map files is primarily for debugging and profiling the kernel. Unrestricted access to these files might disclose information useful to attackers and malicious software leading to more sophisticated exploitation. |
| R29 | Verify /boot/grub2/user.cfg User Ownership |
The file /boot/grub2/user.cfg should be owned by the root
user to prevent reading or modification of the file.
To properly set the owner of /boot/grub2/user.cfg, run the command:
$ sudo chown root /boot/grub2/user.cfg |
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
| R29 | Verify /boot/grub2/user.cfg Permissions |
File permissions for /boot/grub2/user.cfg should be set to 600.
To properly set the permissions of /boot/grub2/user.cfg, run the command:
$ sudo chmod 600 /boot/grub2/user.cfg |
Proper permissions ensure that only the root user can read or modify important boot parameters. |
| R29 | Verify /boot/efi/EFI/redhat/user.cfg User Ownership |
The file /boot/efi/EFI/redhat/user.cfg should be owned by the root
user to prevent reading or modification of the file.
To properly set the owner of /boot/efi/EFI/redhat/user.cfg, run the command:
$ sudo chown root /boot/efi/EFI/redhat/user.cfg |
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
| R29 | Verify /boot/grub2/grub.cfg User Ownership |
The file /boot/grub2/grub.cfg should
be owned by the root user to prevent destruction
or modification of the file.
To properly set the owner of /boot/grub2/grub.cfg, run the command:
$ sudo chown root /boot/grub2/grub.cfg |
Only root should be able to modify important boot parameters. |
| R29 | Verify /boot/grub2/grub.cfg Permissions |
File permissions for /boot/grub2/grub.cfg should be set to 600.
To properly set the permissions of /boot/grub2/grub.cfg, run the command:
$ sudo chmod 600 /boot/grub2/grub.cfg |
Proper permissions ensure that only the root user can modify important boot parameters. |
| R29 | Verify /boot/grub2/user.cfg Group Ownership |
The file /boot/grub2/user.cfg should be group-owned by the root
group to prevent reading or modification of the file.
To properly set the group owner of /boot/grub2/user.cfg, run the command:
$ sudo chgrp root /boot/grub2/user.cfg |
The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them. |
| R31 | Set Interval For Counting Failed Password Attempts | Utilizing pam_faillock.so, the fail_interval directive configures the system to lock out an account after a number of incorrect login attempts within a specified time period. Ensure that the file /etc/security/faillock.conf contains the following entry: fail_interval = <interval-in-seconds> where interval-in-seconds is 900 or greater. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. | By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 | Set Password Strength Minimum Lowercase Characters | The pam_cracklib module's lcredit= parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each lowercase character. Add lcredit=-1 after pam_cracklib.so to require use of a lowercase character in passwords. | Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Set Lockout Time for Failed Password Attempts | This rule configures the system to lock out accounts during a specified time period after a number of incorrect login attempts using pam_faillock.so. Ensure that the file /etc/security/faillock.conf contains the following entry: unlock_time=<interval-in-seconds> where interval-in-seconds is 0 or greater. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid any errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. If unlock_time is set to 0, manual intervention by an administrator is required to unlock a user. This should be done using the faillock tool. | By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 | Set Password Strength Minimum Special Characters | The pam_cracklib module's ocredit= parameter controls requirements for usage of special (or ``other'') characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each special character. Make sure the ocredit parameter for the pam_cracklib module is set to less than or equal to -1. For example, ocredit=-1. | Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Set Password Minimum Length | The pam_cracklib module's minlen parameter controls requirements for minimum characters required in a password. Add minlen=15 to set minimum password length requirements. | Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password. |
| R31 | Configure the root Account for Failed Password Attempts | This rule configures the system to lock out the root account after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. | By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 R68 |
Ensure PAM Enforces Password Requirements - Minimum Length | The pam_pwquality module's minlen parameter controls requirements for minimum characters required in a password. Add minlen=15 after pam_pwquality to set minimum password length requirements. |
The shorter the password, the lower the number of possible combinations
that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password. |
| R31 | Ensure PAM Enforces Password Requirements - Minimum Lowercase Characters | The pam_pwquality module's lcredit parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the lcredit setting in /etc/security/pwquality.conf to require the use of a lowercase character in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Set Password Strength Minimum Digit Characters | The pam_cracklib module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_cracklib will grant +1 additional length credit for each digit. Add dcredit=-1 after pam_cracklib.so to require use of a digit in passwords. | Requiring digits makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Limit Password Reuse | Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_unix or pam_pwhistory PAM modules. | Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user. |
| R31 | Lock Accounts After Failed Password Attempts | This rule configures the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. Ensure that the file /etc/security/faillock.conf contains the following entry: deny = <count> Where count should be less than or equal to 3 and greater than 0. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. | By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 | Set Root Account Password Maximum Age |
Configure the root account to enforce a 99999-day maximum password lifetime restriction by running the following command:
$ sudo chage -M 99999 root |
Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If the operating system does not limit the lifetime of passwords and force users to change their passwords, there is the risk that the operating system passwords could be compromised. |
| R31 | Ensure PAM Enforces Password Requirements - Minimum Special Characters | The pam_pwquality module's ocredit= parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the ocredit setting in /etc/security/pwquality.conf to equal -1 to require use of a special character in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Enable authselect | Configure user authentication setup to use the authselect tool. If authselect profile is selected, the rule will enable the minimal profile. | Authselect is a successor to authconfig. It is a tool to select system authentication and identity sources from a list of supported profiles instead of letting the administrator manually build the PAM stack. That way, it avoids potential breakage of configuration, as it ships several tested profiles that are well tested and supported to solve different use-cases. |
| R31 | Configure the root Account lock for Failed Password Attempts via pam_tally2 | This rule configures the system to lock out the root account after a number of incorrect login attempts using pam_tally2.so. | By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 | Ensure PAM Enforces Password Requirements - Minimum Digit Characters | The pam_pwquality module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the dcredit setting in /etc/security/pwquality.conf to require the use of a digit in passwords. |
Use of a complex password helps to increase the time and resources required
to compromise the password. Password complexity, or strength, is a measure of
the effectiveness of a password in resisting attempts at guessing and brute-force
attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring digits makes password guessing attacks more difficult by ensuring a larger search space. |
| R31 | Set Lockout Time for Failed Password Attempts using pam_tally2 | This rule configures the system to lock out accounts during a specified time period after a number of incorrect login attempts using pam_tally2.so. | By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account. |
| R31 | Set Deny For Failed Password Attempts | The Red Hat Enterprise Linux 8 operating system must lock an account after - at most - 3 consecutive invalid access attempts. |
By limiting the number of failed logon attempts, the risk of unauthorized
system access via user password guessing, otherwise known as brute-force
attacks, is reduced. Limits are imposed by locking the account.
To configure the operating system to lock an account after three
unsuccessful consecutive access attempts using pam_tally2.so,
modify the content of both /etc/pam.d/common-auth and
/etc/pam.d/common-account as follows:
|
| R31 | Ensure PAM Enforces Password Requirements - Minimum Uppercase Characters | The pam_pwquality module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the ucredit setting in /etc/security/pwquality.conf to require the use of an uppercase character in passwords. |
Use of a complex password helps to increase the time and resources required to compromise the password.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts
at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. |
| R31 | Set Password Minimum Length in login.defs |
To specify password length requirements for new accounts, edit the file
/etc/login.defs and add or correct the following line:
PASS_MIN_LEN 15 The DoD requirement is 15. The FISMA requirement is 12. The profile requirement is 15. If a program consults /etc/login.defs and also another PAM module (such as pam_pwquality) during a password change operation, then the most restrictive must be satisfied. See PAM section for more information about enforcing password quality requirements. |
Requiring a minimum password length makes password cracking attacks more difficult by ensuring a larger search space. However, any security benefit from an onerous requirement must be carefully weighed against usability problems, support costs, or counterproductive behavior that may result. |
| R31 | Set Password Strength Minimum Uppercase Characters | The pam_cracklib module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each uppercase character. Add ucredit=-1 after pam_cracklib.so to require use of an upper case character in passwords. | Requiring a minimum number of uppercase characters makes password guessing attacks more difficult by ensuring a larger search space. |
| R32 | Set Interactive Session Timeout |
Setting the TMOUT option in /etc/profile ensures that
all user sessions will terminate based on inactivity.
The value of TMOUT should be exported and read only.
The TMOUT
setting in a file loaded by /etc/profile, e.g.
/etc/profile.d/tmout.sh should read as follows:
typeset -xr TMOUT=600or declare -xr TMOUT=600Using the typeset keyword is preferred for wider compatibility with ksh and other shells.
|
Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. |
| R32 | Configure Logind to terminate idle sessions after certain time of inactivity |
To configure logind service to terminate inactive user sessions
after 300 seconds, edit the file
/etc/systemd/logind.conf. Ensure that there is a section
[Login]which contains the configuration StopIdleSessionSec=300. |
Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been let unattended. |
| R33 | Direct root Logins Not Allowed |
To further limit access to the root account, administrators
can disable root logins at the console by editing the /etc/securetty file.
This file lists all devices the root user is allowed to login to. If the file does
not exist at all, the root user can login through any communication device on the
system, whether via the console or via a raw network interface. This is dangerous
as user can login to the system as root via Telnet, which sends the password in
plain text over the network. By default, Red Hat Enterprise Linux 8's
/etc/securetty file only allows the root user to login at the console
physically attached to the system. To prevent root from logging in, remove the
contents of this file. To prevent direct root logins, remove the contents of this
file by typing the following command:
$ sudo echo > /etc/securetty |
Disabling direct root logins ensures proper accountability and multifactor authentication to privileged accounts. Users will first login, then escalate to privileged (root) access via su / sudo. This is required for FISMA Low and FISMA Moderate systems. |
| R33 | Ensure auditd Collects Information on the Use of Privileged Commands - sudo |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-a always,exit -F path=/usr/bin/sudo -F perm=x -F auid>=1000 -F auid!=unset -F key=privilegedIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: -a always,exit -F path=/usr/bin/sudo -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
| R33 | Disable SSH Root Login |
The root user should never be allowed to login to a
system directly over a network.
To disable root login via SSH, add or correct the following line in
/etc/ssh/sshd_config:
PermitRootLogin no |
Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password. |
| R33 R73 |
Ensure the audit Subsystem is Installed | The audit package should be installed. | The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparison with potential local access control policy such as SELinux policy. |
| R33 R73 |
Enable auditd Service |
The auditd service is an essential userspace component of
the Linux Auditing System, as it is responsible for writing audit records to
disk.
The auditd service can be enabled with the following command:
$ sudo systemctl enable auditd.service |
Without establishing what type of events occurred, it would be difficult
to establish, correlate, and investigate the events leading up to an outage or attack.
Ensuring the auditd service is active ensures audit records
generated by the kernel are appropriately recorded.
Additionally, a properly configured audit subsystem ensures that actions of individual system users can be uniquely traced to those users so they can be held accountable for their actions. |
| R33 | Install sudo Package |
The sudo package can be installed with the following command:
$ sudo yum install sudo |
sudo is a program designed to allow a system administrator to give limited root privileges to users and log root activity. The basic philosophy is to give as few privileges as possible but still allow system users to get their work done. |
| R36 | Ensure the Default Bash Umask is Set Correctly |
To ensure the default umask for users of the Bash shell is set properly,
add or correct the umask setting in /etc/bashrc to read
as follows:
umask 027 |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users. |
| R36 | Ensure the Default Umask is Set Correctly in login.defs |
To ensure the default umask controlled by /etc/login.defs is set properly,
add or correct the UMASK setting in /etc/login.defs to read as follows:
UMASK 027 |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and written to by unauthorized users. |
| R36 | Ensure the Default Umask is Set Correctly in /etc/profile |
To ensure the default umask controlled by /etc/profile is set properly,
add or correct the umask setting in /etc/profile to read as follows:
umask 027Note that /etc/profile also reads scrips within /etc/profile.d directory. These scripts are also valid files to set umask value. Therefore, they should also be considered during the check and properly remediated, if necessary. |
The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users. |
| R37 R79 |
Ensure SELinux State is Enforcing |
The SELinux state should be set to enforcing at
system boot time. In the file /etc/selinux/config, add or correct the
following line to configure the system to boot into enforcing mode:
SELINUX=enforcing |
Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges. |
| R38 | Ensure That the sudo Binary Has the Correct Permissions |
To properly set the permissions of /usr/bin/sudo, run the command:
$ sudo chmod 4111 /usr/bin/sudo |
The sudoers program should only be usable by people who have the correct permissions. |
| R38 | Ensure a dedicated group owns sudo | Restrict the execution of privilege escalated commands to a dedicated group of users. Ensure the group owner of /usr/bin/sudo is root. | Restricting the set of users able to execute commands as privileged user reduces the attack surface. |
| R39 | Ensure Privileged Escalated Commands Cannot Execute Other Commands - sudo NOEXEC | The sudo NOEXEC tag, when specified, prevents user executed commands from executing other commands, like a shell for example. This should be enabled by making sure that the NOEXEC tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Restricting the capability of sudo allowed commands to execute sub-commands prevents users from running programs with privileges they wouldn't have otherwise. |
| R39 | Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo use_pty | The sudo use_pty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the use_pty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Requiring that sudo commands be run in a pseudo-terminal can prevent an attacker from retaining access to the user's terminal after the main program has finished executing. |
| R39 | Ensure sudo umask is appropriate - sudo umask | The sudo umask tag, when specified, will be added the to the user's umask in the command environment. On Red Hat Enterprise Linux 8, the default umask value is 0022. The umask should be configured by making sure that the umask=0022 tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users. |
| R39 | Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo requiretty | The sudo requiretty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the requiretty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Restricting the use cases in which a user is allowed to execute sudo commands reduces the attack surface. |
| R39 | Ensure sudo Runs In A Minimal Environment - sudo env_reset | The sudo env_reset tag, when specified, will run the command in a minimal environment, containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER and SUDO_* variables. On Red Hat Enterprise Linux 8, env_reset is enabled by default This should be enabled by making sure that the env_reset tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Forcing sudo to reset the environment ensures that environment variables are not passed on to the command accidentaly, preventing leak of potentially sensitive information. |
| R39 | Ensure sudo Ignores Commands In Current Dir - sudo ignore_dot | The sudo ignore_dot tag, when specified, will ignore the current directory in the PATH environment variable. On Red Hat Enterprise Linux 8, env_reset is enabled by default This should be enabled by making sure that the ignore_dot tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. | Ignoring the commands in the user's current directory prevents an attacker from executing commands downloaded locally. |
| R40 | Don't target root user in the sudoers file | The targeted users of a user specification should be, as much as possible, non privileged users (i.e.: non-root). User specifications have to explicitly list the runas spec (i.e. the list of target users that can be impersonated), and ALL or root should not be used. | It is common that the command to be executed does not require superuser rights (editing a file whose the owner is not root, sending a signal to an unprivileged process,etc.). In order to limit any attempt of privilege escalation through a command, it is better to apply normal user rights. |
| R42 | Don't define allowed commands in sudoers by means of exclusion |
Policies applied by sudo through the sudoers file should not involve negation.
Each user specification in the sudoers file contains a comma-delimited list of command specifications.
The definition can make use glob patterns, as well as of negations.
Indirect definition of those commands by means of exclusion of a set of commands is trivial to bypass, so it is not allowed to use such constructs.
|
Specifying access right using negation is inefficient and can be easily circumvented.
For example, it is expected that a specification like # To avoid absolutely , this rule can be easily circumvented! user ALL = ALL ,!/ bin/shprevents the execution of the shell but that’s not the case: just copy the binary /bin/sh to a different name to make it executable
again through the rule keyword ALL.
|
| R43 | Explicit arguments in sudo specifications | All commands in the sudoers file must strictly specify the arguments allowed to be used for a given user. If the command is supposed to be executed only without arguments, pass "" as an argument in the corresponding user specification. |
Any argument can modify quite significantly the behavior of a program, whether regarding the
realized operation (read, write, delete, etc.) or accessed resources (path in a file system tree). To
avoid any possibility of misuse of a command by a user, the ambiguities must be removed at the
level of its specification.
For example, on some systems, the kernel messages are only accessible by root.
If a user nevertheless must have the privileges to read them, the argument of the dmesg command has to be restricted
in order to prevent the user from flushing the buffer through the -c option:
user ALL = dmesg "" |
| R46 R64 |
Configure SELinux Policy |
The SELinux targeted policy is appropriate for
general-purpose desktops and servers, as well as systems in many other roles.
To configure the system to use this policy, add or correct the following line
in /etc/selinux/config:
SELINUXTYPE=targetedOther policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases. |
Setting the SELinux policy to targeted or a more specialized policy
ensures the system will confine processes that are likely to be
targeted for exploitation, such as network or system services.
Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to . |
| R48 | Configure the secure_mode_insmod SELinux Boolean |
By default, the SELinux boolean secure_mode_insmod is disabled.
This setting should be configured to false.
To set the secure_mode_insmod SELinux boolean, run the following command:
$ sudo setsebool -P secure_mode_insmod false |
|
| R48 | Disable the selinuxuser_execstack SELinux Boolean |
By default, the SELinux boolean selinuxuser_execstack is enabled.
This setting should be disabled as unconfined executables should not be able
to make their stack executable.
To disable the selinuxuser_execstack SELinux boolean, run the following command:
$ sudo setsebool -P selinuxuser_execstack off |
Disabling code execution from the stack blocks buffer overflow attacks. |
| R48 | Configure the deny_execmem SELinux Boolean |
By default, the SELinux boolean deny_execmem is disabled.
This setting should be configured to false.
To set the deny_execmem SELinux boolean, run the following command:
$ sudo setsebool -P deny_execmem false |
Allowing user domain applications to map a memory region as both writable and executable makes them more susceptible to data execution attacks. |
| R48 | Disable the ssh_sysadm_login SELinux Boolean |
By default, the SELinux boolean ssh_sysadm_login is disabled.
If this setting is enabled, it should be disabled.
To disable the ssh_sysadm_login SELinux boolean, run the following command:
$ sudo setsebool -P ssh_sysadm_login off |
Preventing non-privileged users from executing privileged functions mitigates the risk that unauthorized individuals or processes may gain unnecessary access to information or privileges. Privileged functions include, for example, establishing accounts, performing system integrity checks, or administering cryptographic key management activities. Non-privileged users are individuals who do not possess appropriate authorizations. Circumventing intrusion detection and prevention mechanisms or malicious code protection mechanisms are examples of privileged functions that require protection from non-privileged users. |
| R48 | Disable the selinuxuser_execheap SELinux Boolean |
By default, the SELinux boolean selinuxuser_execheap is disabled.
When enabled this boolean is enabled it allows selinuxusers to execute code from the heap.
If this setting is enabled, it should be disabled.
To disable the selinuxuser_execheap SELinux boolean, run the following command:
$ sudo setsebool -P selinuxuser_execheap off |
Disabling code execution from the heap blocks buffer overflow attacks. |
| R49 | Uninstall setroubleshoot-server Package |
The SETroubleshoot service notifies desktop users of SELinux
denials. The service provides information around configuration errors,
unauthorized intrusions, and other potential errors.
The setroubleshoot-server package can be removed with the following command:
$ sudo yum erase setroubleshoot-server |
The SETroubleshoot service is an unnecessary daemon to have running on a server. |
| R49 | Uninstall setroubleshoot-plugins Package |
The SETroubleshoot plugins are used to analyze SELinux AVC data. The service provides information around configuration errors,
unauthorized intrusions, and other potential errors.
The setroubleshoot-plugins package can be removed with the following command:
$ sudo yum erase setroubleshoot-plugins |
The SETroubleshoot service is an unnecessary daemon to have running on a server. |
| R49 | Uninstall setroubleshoot Package |
The SETroubleshoot service notifies desktop users of SELinux
denials. The service provides information around configuration errors,
unauthorized intrusions, and other potential errors.
The setroubleshoot package can be removed with the following command:
$ sudo yum erase setroubleshoot |
The SETroubleshoot service is an unnecessary daemon to have running on a server, especially if X Windows is removed or disabled. |
| R50 | Verify Permissions On /etc/ipsec.secrets File |
To properly set the permissions of /etc/ipsec.secrets, run the command: $ sudo chmod 0644 /etc/ipsec.secrets |
Setting correct permissions on the /etc/ipsec.secrets file is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Restricting the permissions ensures exclusive control of the Libreswan configuration. |
| R50 | Verify User Who Owns /etc/ipsec.d Directory |
To properly set the owner of /etc/ipsec.d, run the command: $ sudo chown root /etc/ipsec.d |
The ownership of the /etc/ipsec.d directory by the root user is important because this directory hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify User Who Owns /etc/sudoers File |
To properly set the owner of /etc/sudoers, run the command: $ sudo chown root /etc/sudoers |
The ownership of the /etc/sudoers file by the root user is important because this file hosts sudo configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the sudo configuration. |
| R50 | Verify Permissions on SSH Server Public *.pub Key Files |
To properly set the permissions of /etc/ssh/*.pub, run the command: $ sudo chmod 0644 /etc/ssh/*.pub |
If a public host key file is modified by an unauthorized user, the SSH service may be compromised. |
| R50 | Verify User Who Owns group File |
To properly set the owner of /etc/group, run the command: $ sudo chown root /etc/group |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
| R50 | All User Files and Directories In The Home Directory Must Be Group-Owned By The Primary Group |
Change the group of a local interactive users files and directories to a
group that the interactive user is a member of. To change the group owner of a
local interactive users files and directories, use the following command:
$ sudo chgrp USER_GROUP /home/USER/FILE_DIRThis rule ensures every file or directory under the home directory related to an interactive user is group-owned by an interactive user. |
If a local interactive users files are group-owned by a group of which the user is not a member, unintended users may be able to access them. |
| R50 | Verify Permissions On /etc/selinux Directory |
To properly set the permissions of /etc/selinux, run the command: $ sudo chmod 0755 /etc/selinux |
Setting correct permissions on the /etc/selinux directory is important because this directory hosts SELinux configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the SELinux configuration. |
| R50 | Verify User Who Owns /etc/sudoers.d Directory |
To properly set the owner of /etc/sudoers.d, run the command: $ sudo chown root /etc/sudoers.d |
The ownership of the /etc/sudoers.d directory by the root user is important because this directory hosts sudo configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the sudo configuration. |
| R50 | Verify Permissions On /etc/sestatus.conf File |
To properly set the permissions of /etc/sestatus.conf, run the command: $ sudo chmod 0644 /etc/sestatus.conf |
Setting correct permissions on the /etc/sestatus.conf file is important because this file hosts SELinux configuration. Protection of this file is critical for system security. Restricting the permissions ensures exclusive control of the SELinux configuration. |
| R50 | User Initialization Files Must Be Owned By the Primary User |
Set the owner of the user initialization files for interactive users to
the primary owner with the following command:
$ sudo chown USER /home/USER/.*This rule ensures every initialization file related to an interactive user is owned by an interactive user. |
Local initialization files are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon. |
| R50 | Verify Permissions on SSH Server Private *_key Key Files |
SSH server private keys - files that match the /etc/ssh/*_key glob, have to have restricted permissions.
If those files are owned by the root user and the root group, they have to have the 0600 permission or stricter.
If they are owned by the root user, but by a dedicated group ssh_keys, they can have the 0640 permission or stricter.
|
If an unauthorized user obtains the private SSH host key file, the host could be impersonated. |
| R50 | Verify Permissions on shadow File |
To properly set the permissions of /etc/shadow, run the command:
$ sudo chmod 0000 /etc/shadow |
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture. |
| R50 | All User Files and Directories In The Home Directory Must Have a Valid Owner |
Either remove all files and directories from the system that
do not have a valid user, or assign a valid user to all unowned
files and directories. To assign a valid owner to a local
interactive user's files and directories, use the following command:
$ sudo chown -R USER /home/USERThis rule ensures every file or directory under the home directory related to an interactive user is owned by an interactive user. |
If local interactive users do not own the files in their directories, unauthorized users may be able to access them. Additionally, if files are not owned by the user, this could be an indication of system compromise. |
| R50 | Verify Permissions on passwd File |
To properly set the permissions of /etc/passwd, run the command:
$ sudo chmod 0644 /etc/passwd |
If the /etc/passwd file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security. |
| R50 | Verify User Who Owns /etc/sysctl.d Directory |
To properly set the owner of /etc/sysctl.d, run the command: $ sudo chown root /etc/sysctl.d |
The ownership of the /etc/sysctl.d directory by the root user is important because this directory hosts kernel configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the kernel configuration. |
| R50 | Verify Group Who Owns /etc/selinux Directory |
To properly set the group owner of /etc/selinux, run the command: $ sudo chgrp root /etc/selinux |
The ownership of the /etc/selinux directory by the root group is important because this directory hosts SELinux configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the SELinux configuration. |
| R50 | Verify Who Owns /etc/shells File |
To properly set the owner of /etc/shells, run the command:
$ sudo chown root /etc/shells |
The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected. |
| R50 | Verify Group Who Owns /etc/sudoers.d Directory |
To properly set the group owner of /etc/sudoers.d, run the command: $ sudo chgrp root /etc/sudoers.d |
The ownership of the /etc/sudoers.d directory by the root group is important because this directory hosts sudo configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the sudo configuration. |
| R50 | Verify User Who Owns gshadow File |
To properly set the owner of /etc/gshadow, run the command: $ sudo chown root /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
| R50 | Verify Permissions on /etc/shells File |
To properly set the permissions of /etc/shells, run the command:
$ sudo chmod 0644 /etc/shells |
The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected. |
| R50 | Verify Permissions On /etc/crypttab File |
To properly set the permissions of /etc/crypttab, run the command: $ sudo chmod 0600 /etc/crypttab |
Setting correct permissions on the /etc/crypttab file is important because this file hosts encrypted block devices configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the encrypted block devices configuration. |
| R50 | Verify Group Who Owns /etc/sudoers File |
To properly set the group owner of /etc/sudoers, run the command: $ sudo chgrp root /etc/sudoers |
The ownership of the /etc/sudoers file by the root group is important because this file hosts sudo configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the sudo configuration. |
| R50 | Verify that system commands directories have root ownership |
System commands are stored in the following directories by default:
/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbinAll these directories should be owned by the root user. If any system command directory is not owned by a user other than root correct its ownership with the following command: $ sudo chown root DIR |
If the operating system were to allow any user to make changes to software libraries, then those changes might be implemented without undergoing the appropriate testing and approvals that are part of a robust change management process. This requirement applies to operating systems with software libraries that are accessible and configurable, as in the case of interpreted languages. Software libraries also include privileged programs which execute with escalated privileges. Only qualified and authorized individuals must be allowed to obtain access to information system components for purposes of initiating changes, including upgrades and modifications. |
| R50 | Verify Permissions On /etc/ipsec.d Directory |
To properly set the permissions of /etc/ipsec.d, run the command: $ sudo chmod 0700 /etc/ipsec.d |
Setting correct permissions on the /etc/ipsec.d directory is important because this directory hosts Libreswan configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the Libreswan configuration. |
| R50 | Verify User Who Owns /etc/chrony.keys File |
To properly set the owner of /etc/chrony.keys, run the command: $ sudo chown root /etc/chrony.keys |
The ownership of the /etc/chrony.keys file by the root user is important because this file hosts chrony cryptographic keys. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the chrony cryptographic keys. |
| R50 | Verify Permissions on SSH Server config file |
To properly set the permissions of /etc/ssh/sshd_config, run the command:
$ sudo chmod 0600 /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
| R50 | User Initialization Files Must Be Group-Owned By The Primary Group |
Change the group owner of interactive users files to the group found
in /etc/passwdfor the user. To change the group owner of a local interactive user home directory, use the following command: $ sudo chgrp USER_GROUP /home/USER/.INIT_FILEThis rule ensures every initialization file related to an interactive user is group-owned by an interactive user. |
Local initialization files for interactive users are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon. |
| R50 | Verify Permissions On /etc/iptables Directory |
To properly set the permissions of /etc/iptables, run the command: $ sudo chmod 0600 /etc/iptables |
Setting correct permissions on the /etc/iptables directory is important because this directory hosts iptables configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the iptables configuration. |
| R50 | Verify Permissions On /etc/sudoers.d Directory |
To properly set the permissions of /etc/sudoers.d, run the command: $ sudo chmod 0750 /etc/sudoers.d |
Setting correct permissions on the /etc/sudoers.d directory is important because this directory hosts sudo configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the sudo configuration. |
| R50 | All User Files and Directories In The Home Directory Must Have Mode 0750 Or Less Permissive |
Set the mode on files and directories in the local interactive user home
directory with the following command:
$ sudo chmod 0750 /home/USER/FILE_DIRFiles that begin with a "." are excluded from this requirement. |
If a local interactive user files have excessive permissions, unintended users may be able to access or modify them. |
| R50 | Verify Group Who Owns /etc/chrony.keys File |
To properly set the group owner of /etc/chrony.keys, run the command: $ sudo chgrp root /etc/chrony.keys |
The ownership of the /etc/chrony.keys file by the root group is important because this file hosts chrony cryptographic keys. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the chrony cryptography keys. |
| R50 | Verify Group Who Owns /etc/iptables Directory |
To properly set the group owner of /etc/iptables, run the command: $ sudo chgrp root /etc/iptables |
The ownership of the /etc/iptables directory by the root group is important because this directory hosts iptables configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the iptables configuration. |
| R50 | Verify Group Who Owns /etc/nftables Directory |
To properly set the group owner of /etc/nftables, run the command: $ sudo chgrp root /etc/nftables |
The ownership of the /etc/nftables directory by the root group is important because this directory hosts nftables configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the nftables configuration. |
| R50 | Verify Ownership on SSH Server Private *_key Key Files |
SSH server private keys, files that match the /etc/ssh/*_key glob, must be owned
by root user.
|
If an unauthorized user obtains the private SSH host key file, the host could be impersonated. |
| R50 | Verify Permissions On /etc/ipsec.conf File |
To properly set the permissions of /etc/ipsec.conf, run the command: $ sudo chmod 0644 /etc/ipsec.conf |
Setting correct permissions on the /etc/ipsec.conf file is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Restricting the permissions ensures exclusive control of the Libreswan configuration. |
| R50 | Verify Permissions On /etc/chrony.keys File |
To properly set the permissions of /etc/chrony.keys, run the command: $ sudo chmod 0600 /etc/chrony.keys |
Setting correct permissions on the /etc/chrony.keys file is important because this file hosts chrony cryptographic keys. Protection of this file is critical for system security. Assigning the correct mode ensures exclusive control of the chrony cryptographic keys. |
| R50 | Verify User Who Owns /etc/ipsec.conf File |
To properly set the owner of /etc/ipsec.conf, run the command: $ sudo chown root /etc/ipsec.conf |
The ownership of the /etc/ipsec.conf file by the root user is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify Group Who Owns /etc/sysctl.d Directory |
To properly set the group owner of /etc/sysctl.d, run the command: $ sudo chgrp root /etc/sysctl.d |
The ownership of the /etc/sysctl.d directory by the root group is important because this directory hosts kernel configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the kernel configuration. |
| R50 | Verify Permissions On /etc/sudoers File |
To properly set the permissions of /etc/sudoers, run the command: $ sudo chmod 0440 /etc/sudoers |
Setting correct permissions on the /etc/sudoers file is important because this file hosts sudo configuration. Protection of this file is critical for system security. Restricting the permissions ensures exclusive control of the sudo configuration. |
| R50 | Verify User Who Owns /etc/iptables Directory |
To properly set the owner of /etc/iptables, run the command: $ sudo chown root /etc/iptables |
The ownership of the /etc/iptables directory by the root user is important because this directory hosts iptables configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the iptables configuration. |
| R50 | Verify Group Who Owns shadow File |
To properly set the group owner of /etc/shadow, run the command: $ sudo chgrp root /etc/shadow |
The /etc/shadow file stores password hashes. Protection of this file is critical for system security. |
| R50 | Ensure All User Initialization Files Have Mode 0740 Or Less Permissive |
Set the mode of the user initialization files to 0740 with the
following command:
$ sudo chmod 0740 /home/USER/.INIT_FILE |
Local initialization files are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon. |
| R50 | Verify Group Who Owns group File |
To properly set the group owner of /etc/group, run the command: $ sudo chgrp root /etc/group |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
| R50 | Verify User Who Owns /etc/selinux Directory |
To properly set the owner of /etc/selinux, run the command: $ sudo chown root /etc/selinux |
The ownership of the /etc/selinux directory by the root user is important because this directory hosts SELinux configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the SELinux configuration. |
| R50 | Verify that system commands files are group owned by root or a system account |
System commands files are stored in the following directories by default:
/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbinAll files in these directories should be owned by the root group, or a system account. If the directory, or any file in these directories, is found to be owned by a group other than root or a a system account correct its ownership with the following command: $ sudo chgrp root FILE |
If the operating system allows any user to make changes to software libraries, then those changes might be implemented without undergoing the appropriate testing and approvals that are part of a robust change management process. This requirement applies to operating systems with software libraries that are accessible and configurable, as in the case of interpreted languages. Software libraries also include privileged programs which execute with escalated privileges. Only qualified and authorized individuals must be allowed to obtain access to information system components for purposes of initiating changes, including upgrades and modifications. |
| R50 | Verify Permissions On /etc/nftables Directory |
To properly set the permissions of /etc/nftables, run the command: $ sudo chmod 0700 /etc/nftables |
Setting correct permissions on the /etc/nftables directory is important because this directory hosts nftables configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the nftables configuration. |
| R50 | Verify that System Executables Have Root Ownership |
System executables are stored in the following directories by default:
/bin /sbin /usr/bin /usr/libexec /usr/local/bin /usr/local/sbin /usr/sbinAll files in these directories should be owned by the root user. If any file FILE in these directories is found to be owned by a user other than root, correct its ownership with the following command: $ sudo chown root FILE |
System binaries are executed by privileged users as well as system services, and restrictive permissions are necessary to ensure that their execution of these programs cannot be co-opted. |
| R50 | Verify Group Ownership on SSH Server Public *.pub Key Files |
SSH server public keys, files that match the /etc/ssh/*.pub glob, must be
group-owned by root group.
|
If a public host key file is modified by an unauthorized user, the SSH service may be compromised. |
| R50 | Verify that System Executables Have Restrictive Permissions |
System executables are stored in the following directories by default:
/bin /sbin /usr/bin /usr/libexec /usr/local/bin /usr/local/sbin /usr/sbinAll files in these directories should not be group-writable or world-writable. If any file FILE in these directories is found to be group-writable or world-writable, correct its permission with the following command: $ sudo chmod go-w FILE |
System binaries are executed by privileged users, as well as system services, and restrictive permissions are necessary to ensure execution of these programs cannot be co-opted. |
| R50 | Verify that system commands directories have root as a group owner |
System commands are stored in the following directories:
by default:
/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbinAll these directories should have root user as a group owner. If any system command directory is not group owned by a user other than root correct its ownership with the following command: $ sudo chgrp root DIR |
If the operating system were to allow any user to make changes to software libraries, then those changes might be implemented without undergoing the appropriate testing and approvals that are part of a robust change management process. This requirement applies to operating systems with software libraries that are accessible and configurable, as in the case of interpreted languages. Software libraries also include privileged programs which execute with escalated privileges. Only qualified and authorized individuals must be allowed to obtain access to information system components for purposes of initiating changes, including upgrades and modifications. |
| R50 | Verify Group Who Owns /etc/sestatus.conf File |
To properly set the group owner of /etc/sestatus.conf, run the command: $ sudo chgrp root /etc/sestatus.conf |
The ownership of the /etc/sestatus.conf file by the root group is important because this file hosts SELinux configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the SELinux configuration. |
| R50 | Verify Owner on SSH Server config file |
To properly set the owner of /etc/ssh/sshd_config, run the command:
$ sudo chown root /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
| R50 | Verify User Who Owns /etc/crypttab File |
To properly set the owner of /etc/crypttab, run the command: $ sudo chown root /etc/crypttab |
The ownership of the /etc/crypttab file by the root user is important because this file hosts encrypted block devices configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the encrypted block devices configuration. |
| R50 | Verify Group Who Owns passwd File |
To properly set the group owner of /etc/passwd, run the command: $ sudo chgrp root /etc/passwd |
The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security. |
| R50 | Verify Permissions On /etc/sysctl.d Directory |
To properly set the permissions of /etc/sysctl.d, run the command: $ sudo chmod 0755 /etc/sysctl.d |
Setting correct permissions on the /etc/sysctl.d directory is important because this directory hosts kernel configuration. Protection of this directory is critical for system security. Restricting the permissions ensures exclusive control of the kernel configuration. |
| R50 | Verify Group Who Owns /etc/crypttab File |
To properly set the group owner of /etc/crypttab, run the command: $ sudo chgrp root /etc/crypttab |
The ownership of the /etc/crypttab file by the root group is important because this file hosts encrypted block devices configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the encrypted block devices configuration. |
| R50 | Verify Group Who Owns /etc/shells File |
To properly set the group owner of /etc/shells, run the command:
$ sudo chgrp root /etc/shells |
The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected. |
| R50 | Verify Group Who Owns /etc/ipsec.secrets File |
To properly set the group owner of /etc/ipsec.secrets, run the command: $ sudo chgrp root /etc/ipsec.secrets |
The ownership of the /etc/ipsec.secrets file by the root group is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify Group Who Owns /etc/ipsec.conf File |
To properly set the group owner of /etc/ipsec.conf, run the command: $ sudo chgrp root /etc/ipsec.conf |
The ownership of the /etc/ipsec.conf file by the root group is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify Group Who Owns /etc/ipsec.d Directory |
To properly set the group owner of /etc/ipsec.d, run the command: $ sudo chgrp root /etc/ipsec.d |
The ownership of the /etc/ipsec.d directory by the root group is important because this directory hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify User Who Owns /etc/sestatus.conf File |
To properly set the owner of /etc/sestatus.conf, run the command: $ sudo chown root /etc/sestatus.conf |
The ownership of the /etc/sestatus.conf file by the root user is important because this file hosts SELinux configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the SELinux configuration. |
| R50 | Verify Permissions on gshadow File |
To properly set the permissions of /etc/gshadow, run the command:
$ sudo chmod 0000 /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
| R50 | Verify Group Who Owns gshadow File |
To properly set the group owner of /etc/gshadow, run the command: $ sudo chgrp root /etc/gshadow |
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security. |
| R50 | Verify Ownership on SSH Server Public *.pub Key Files |
SSH server public keys, files that match the /etc/ssh/*.pub glob, must be owned
by root user.
|
If a public host key file is modified by an unauthorized user, the SSH service may be compromised. |
| R50 | Verify User Who Owns /etc/nftables Directory |
To properly set the owner of /etc/nftables, run the command: $ sudo chown root /etc/nftables |
The ownership of the /etc/nftables directory by the root user is important because this directory hosts nftables configuration. Protection of this directory is critical for system security. Assigning the ownership to root ensures exclusive control of the nftables configuration. |
| R50 | Verify User Who Owns passwd File |
To properly set the owner of /etc/passwd, run the command: $ sudo chown root /etc/passwd |
The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security. |
| R50 | Verify Permissions on group File |
To properly set the permissions of /etc/group, run the command:
$ sudo chmod 0644 /etc/group |
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security. |
| R50 | Verify Group Ownership on SSH Server Private *_key Key Files |
SSH server private keys, files that match the /etc/ssh/*_key glob, must be
group-owned by ssh_keys group.
|
If an unauthorized user obtains the private SSH host key file, the host could be impersonated. |
| R50 | Verify User Who Owns /etc/ipsec.secrets File |
To properly set the owner of /etc/ipsec.secrets, run the command: $ sudo chown root /etc/ipsec.secrets |
The ownership of the /etc/ipsec.secrets file by the root user is important because this file hosts Libreswan configuration. Protection of this file is critical for system security. Assigning the ownership to root ensures exclusive control of the Libreswan configuration. |
| R50 | Verify Group Who Owns SSH Server config file |
To properly set the group owner of /etc/ssh/sshd_config, run the command:
$ sudo chgrp root /etc/ssh/sshd_config |
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes. |
| R50 | Verify User Who Owns shadow File |
To properly set the owner of /etc/shadow, run the command: $ sudo chown root /etc/shadow |
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture. |
| R53 | Ensure All Files Are Owned by a Group |
If any file is not group-owned by a group present in /etc/group, the cause of the lack of
group-ownership must be investigated. Following this, those files should be deleted or
assigned to an appropriate group.
Locate the mount points related to local devices by the following command:
$ findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,)
For all mount points listed by the previous command, it is necessary to search for files which
do not belong to a valid group using the following command:
$ sudo find MOUNTPOINT -xdev -nogroup 2>/dev/null |
Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account, or other similar cases. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed. |
| R53 | Ensure All Files Are Owned by a User |
If any files are not owned by a user, then the cause of their lack of ownership should be
investigated. Following this, the files should be deleted or assigned to an appropriate user.
Locate the mount points related to local devices by the following command:
$ findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,)
For all mount points listed by the previous command, it is necessary to search for files which
do not belong to a valid user using the following command:
$ sudo find MOUNTPOINT -xdev -nouser 2>/dev/null |
Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account, or other similar cases. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed. |
| R54 | Ensure All World-Writable Directories Are Owned by root User | All directories in local partitions which are world-writable should be owned by root. If any world-writable directories are not owned by root, this should be investigated. Following this, the files should be deleted or assigned to root user. | Allowing a user account to own a world-writable directory is undesirable because it allows the owner of that directory to remove or replace any files that may be placed in the directory by other users. |
| R54 | Verify that All World-Writable Directories Have Sticky Bits Set |
When the so-called 'sticky bit' is set on a directory, only the owner of a given file may
remove that file from the directory. Without the sticky bit, any user with write access to a
directory may remove any file in the directory. Setting the sticky bit prevents users from
removing each other's files. In cases where there is no reason for a directory to be
world-writable, a better solution is to remove that permission rather than to set the sticky
bit. However, if a directory is used by a particular application, consult that application's
documentation instead of blindly changing modes.
To set the sticky bit on a world-writable directory DIR, run the following command: $ sudo chmod +t DIR |
Failing to set the sticky bit on public directories allows unauthorized users to delete files
in the directory structure.
The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, by users for temporary file storage (such as /tmp), and for directories requiring global read/write access. |
| R54 | Ensure No World-Writable Files Exist | It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account. Finally, this applies to real files and not virtual files that are a part of pseudo file systems such as sysfs or procfs. | Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files. |
| R55 | Configure Polyinstantiation of /tmp Directories |
To configure polyinstantiated /tmp directories, first create the parent directories
which will hold the polyinstantiation child directories. Use the following command:
$ sudo mkdir --mode 000 /tmp/tmp-instThen, add the following entry to /etc/security/namespace.conf: /tmp /tmp/tmp-inst/ level root,adm |
Polyinstantiation of temporary directories is a proactive security measure which reduces chances of attacks that are made possible by /tmp directories being world-writable. |
| R55 | Configure Polyinstantiation of /var/tmp Directories |
To configure polyinstantiated /tmp directories, first create the parent directories
which will hold the polyinstantiation child directories. Use the following command:
$ sudo mkdir --mode 000 /var/tmp/tmp-instThen, add the following entry to /etc/security/namespace.conf: /var/tmp /var/tmp/tmp-inst/ level root,adm |
Polyinstantiation of temporary directories is a proactive security measure which reduces chances of attacks that are made possible by /var/tmp directories being world-writable. |
| R55 | Configure the polyinstantiation_enabled SELinux Boolean |
By default, the SELinux boolean polyinstantiation_enabled is disabled.
This setting should be configured to false.
To set the polyinstantiation_enabled SELinux boolean, run the following command:
$ sudo setsebool -P polyinstantiation_enabled false |
|
| R55 | Set Up a Private Namespace in PAM Configuration |
To setup a private namespace add the following line to /etc/pam.d/login:
session required pam_namespace.so |
The pam_namespace PAM module sets up a private namespace for a session with polyinstantiated directories. A polyinstantiated directory provides a different instance of itself based on user name, or when using SELinux, user name, security context or both. The polyinstatied directories can be used to dedicate separate temporary directories to each account. |
| R56 | Ensure All SGID Executables Are Authorized | The SGID (set group id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SGID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SGID files. This configuration check considers authorized SGID files those which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SGID file not deployed through an RPM will be flagged for further review. | Executable files with the SGID permission run with the privileges of the owner of the file. SGID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system. |
| R56 | Ensure All SUID Executables Are Authorized | The SUID (set user id) bit should be set only on files that were installed via authorized means. A straightforward means of identifying unauthorized SUID files is determine if any were not installed as part of an RPM package, which is cryptographically verified. Investigate the origin of any unpackaged SUID files. This configuration check considers authorized SUID files those which were installed via RPM. It is assumed that when an individual has sudo access to install an RPM and all packages are signed with an organizationally-recognized GPG key, the software should be considered an approved package on the system. Any SUID file not deployed through an RPM will be flagged for further review. | Executable files with the SUID permission run with the privileges of the owner of the file. SUID files of uncertain provenance could allow for unprivileged users to elevate privileges. The presence of these files should be strictly controlled on the system. |
| R59 | Ensure Oracle Linux GPG Key Installed |
To ensure the system can cryptographically verify base software
packages come from Oracle (and to connect to the Unbreakable Linux Network to
receive them), the Oracle GPG key must properly be installed.
To install the Oracle GPG key, run:
$ sudo uln_registerIf the system is not connected to the Internet, then install the Oracle GPG key from trusted media such as the Oracle installation CD-ROM or DVD. Assuming the disc is mounted in /media/cdrom, use the following command as the root user to import it into the keyring: $ sudo rpm --import /media/cdrom/RPM-GPG-KEY-oracleAlternatively, the key may be pre-loaded during the Oracle installation. In such cases, the key can be installed by running the following command: sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-oracle |
Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Oracle GPG key is necessary to cryptographically verify packages are from Oracle. |
| R59 | Ensure Red Hat GPG Key Installed |
To ensure the system can cryptographically verify base software packages
come from Red Hat (and to connect to the Red Hat Network to receive them),
the Red Hat GPG key must properly be installed. To install the Red Hat GPG
key, run:
$ sudo subscription-manager registerIf the system is not connected to the Internet or an RHN Satellite, then install the Red Hat GPG key from trusted media such as the Red Hat installation CD-ROM or DVD. Assuming the disc is mounted in /media/cdrom, use the following command as the root user to import it into the keyring: $ sudo rpm --import /media/cdrom/RPM-GPG-KEYAlternatively, the key may be pre-loaded during the RHEL installation. In such cases, the key can be installed by running the following command: sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release |
Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat. |
| R59 | Ensure gpgcheck Enabled for All yum Package Repositories |
To ensure signature checking is not disabled for
any repos, remove any lines from files in /etc/yum.repos.d of the form:
gpgcheck=0 |
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA)." |
| R59 | Ensure gpgcheck Enabled for Local Packages | yum should be configured to verify the signature(s) of local packages prior to installation. To configure yum to verify signatures of local packages, set the localpkg_gpgcheck to 1 in /etc/yum.conf. |
Changes to any software components can have significant effects to the overall security
of the operating system. This requirement ensures the software has not been tampered and
has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization. |
| R59 | Ensure gpgcheck Enabled In Main yum Configuration |
The gpgcheck option controls whether
RPM packages' signatures are always checked prior to installation.
To configure yum to check package signatures before installing
them, ensure the following line appears in /etc/yum.conf in
the [main] section:
gpgcheck=1 |
Changes to any software components can have significant effects on the
overall security of the operating system. This requirement ensures the
software has not been tampered with and that it has been provided by a
trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization. Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA). |
| R61 | Enable dnf-automatic Timer |
The dnf-automatic timer can be enabled with the following command:
$ sudo systemctl enable dnf-automatic.timer |
The dnf-automatic is an alternative command line interface (CLI) to dnf upgrade with specific facilities to make it suitable to be executed automatically and regularly from systemd timers, cron jobs and similar. The tool is controlled by dnf-automatic.timer SystemD timer. |
| R61 | Configure dnf-automatic to Install Available Updates Automatically | To ensure that the packages comprising the available updates will be automatically installed by dnf-automatic, set apply_updates to yes under [commands] section in /etc/dnf/automatic.conf. | Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise. The automated installation of updates ensures that recent security patches are applied in a timely manner. |
| R61 | Install dnf-automatic Package |
The dnf-automatic package can be installed with the following command:
$ sudo yum install dnf-automatic |
dnf-automatic is an alternative command line interface (CLI) to dnf upgrade suitable for automatic, regular execution. |
| R61 | Configure dnf-automatic to Install Only Security Updates | To configure dnf-automatic to install only security updates automatically, set upgrade_type to security under [commands] section in /etc/dnf/automatic.conf. | By default, dnf-automatic installs all available updates. Reducing the amount of updated packages only to updates that were issued as a part of a security advisory increases the system stability. |
| R61 | Ensure Software Patches Installed |
If the system is joined to the Red Hat Network, a Red Hat Satellite Server,
or a yum server, run the following command to install updates:
$ sudo yum updateIf the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the Red Hat Network and installed using rpm. NOTE: U.S. Defense systems are required to be patched within 30 days or sooner as local policy dictates. |
Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise. |
| R62 | Uninstall tftp-server Package |
The tftp-server package can be removed with the following command: $ sudo yum erase tftp-server |
Removing the tftp-server package decreases the risk of the accidental
(or intentional) activation of tftp services.
If TFTP is required for operational support (such as transmission of router configurations), its use must be documented with the Information Systems Securty Manager (ISSM), restricted to only authorized personnel, and have access control rules established. |
| R62 | Uninstall talk-server Package |
The talk-server package can be removed with the following command: $ sudo yum erase talk-server |
The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk-server package decreases the risk of the accidental (or intentional) activation of talk services. |
| R62 | Uninstall rsh-server Package |
The rsh-server package can be removed with the following command:
$ sudo yum erase rsh-server |
The rsh-server service provides unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session and has very weak authentication. If a privileged user were to login using this service, the privileged user password could be compromised. The rsh-server package provides several obsolete and insecure network services. Removing it decreases the risk of those services' accidental (or intentional) activation. |
| R62 | Uninstall talk Package |
The talk package contains the client program for the
Internet talk protocol, which allows the user to chat with other users on
different systems. Talk is a communication program which copies lines from one
terminal to the terminal of another user.
The talk package can be removed with the following command:
$ sudo yum erase talk |
The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the talk package decreases the risk of the accidental (or intentional) activation of talk client program. |
| R62 | Uninstall rsh Package | The rsh package contains the client commands for the rsh services | These legacy clients contain numerous security exposures and have been replaced with the more secure SSH package. Even if the server is removed, it is best to ensure the clients are also removed to prevent users from inadvertently attempting to use these commands and therefore exposing their credentials. Note that removing the rsh package removes the clients for rsh,rcp, and rlogin. |
| R62 | Uninstall DHCP Server Package |
If the system does not need to act as a DHCP server,
the dhcp package can be uninstalled.
The dhcp-server package can be removed with the following command:
$ sudo yum erase dhcp-server |
Removing the DHCP server ensures that it cannot be easily or accidentally reactivated and disrupt network operation. |
| R62 | Uninstall Sendmail Package |
Sendmail is not the default mail transfer agent and is
not installed by default.
The sendmail package can be removed with the following command:
$ sudo yum erase sendmail |
The sendmail software was not developed with security in mind and its design prevents it from being effectively contained by SELinux. Postfix should be used instead. |
| R62 | Remove telnet Clients | The telnet client allows users to start connections to other systems via the telnet protocol. | The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The ssh package provides an encrypted session and stronger security and is included in Red Hat Enterprise Linux 8. |
| R62 | Uninstall telnet-server Package |
The telnet-server package can be removed with the following command:
$ sudo yum erase telnet-server |
It is detrimental for operating systems to provide, or install by default,
functionality exceeding requirements or mission objectives. These
unnecessary capabilities are often overlooked and therefore may remain
unsecure. They increase the risk to the platform by providing additional
attack vectors.
The telnet service provides an unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using this service, the privileged user password could be compromised. Removing the telnet-server package decreases the risk of the telnet service's accidental (or intentional) activation. |
| R62 | Remove tftp Daemon | Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol, typically used to automatically transfer configuration or boot files between systems. TFTP does not support authentication and can be easily hacked. The package tftp is a client program that allows for connections to a tftp server. | It is recommended that TFTP be removed, unless there is a specific need for TFTP (such as a boot server). In that case, use extreme caution when configuring the services. |
| R62 | Remove NIS Client | The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server directory service protocol used to distribute system configuration files. The NIS client (ypbind) was used to bind a system to an NIS server and receive the distributed configuration files. | The NIS service is inherently an insecure system that has been vulnerable to DOS attacks, buffer overflows and has poor authentication for querying NIS maps. NIS generally has been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is recommended that the service be removed. |
| R62 | Uninstall ypserv Package |
The ypserv package can be removed with the following command:
$ sudo yum erase ypserv |
The NIS service provides an unencrypted authentication service which does not provide for the confidentiality and integrity of user passwords or the remote session. Removing the ypserv package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services. |
| R62 | Uninstall xinetd Package |
The xinetd package can be removed with the following command:
$ sudo yum erase xinetd |
Removing the xinetd package decreases the risk of the xinetd service's accidental (or intentional) activation. |
| R67 | Configure SSSD LDAP Backend Client to Demand a Valid Certificate from the Server |
Configure SSSD to demand a valid certificate from the server to
protect the integrity of LDAP remote access sessions by setting
the ldap_tls_reqcertoption in /etc/sssd/sssd.confto demand. |
Without a valid certificate presented to the LDAP client backend, the identity of a server can be forged compromising LDAP remote access sessions. |
| R67 | Configure Certificate Directives for LDAP Use of TLS |
Ensure a copy of a trusted CA certificate has been placed in the file
/etc/pki/tls/CA/cacert.pem. Configure LDAP to enforce TLS use and
to trust certificates signed by that CA. First, edit the file
/etc/nslcd.conf, and add or correct either of the following lines:
tls_cacertdir /etc/pki/tls/CAor tls_cacertfile /etc/pki/tls/CA/cacert.pemThen review the LDAP server and ensure TLS has been configured. |
The tls_cacertdir or tls_cacertfile directives are required when tls_checkpeer is configured (which is the default for openldap versions 2.1 and up). These directives define the path to the trust certificates signed by the site CA. |
| R67 | Configure PAM in SSSD Services |
SSSD should be configured to run SSSD pam services.
To configure SSSD to known SSH hosts, add pam
to services under the [sssd] section in
/etc/sssd/sssd.conf. For example:
[sssd] services = sudo, autofs, pam |
Using an authentication device, such as a CAC or token that is separate from the information system, ensures that even if the information system is compromised, that compromise will not affect credentials stored on the authentication device. |
| R67 | Configure LDAP Client to Use TLS For All Transactions |
This check verifies cryptography has been implemented
to protect the integrity of remote LDAP authentication sessions.
To determine if LDAP is being used for authentication, use the following command: $ sudo grep -i useldapauth /etc/sysconfig/authconfig If USELDAPAUTH=yes, then LDAP is being used. To check if LDAP is configured to use TLS, use the following command: $ sudo grep -i ssl /etc/pam_ldap.conf |
Without cryptographic integrity protections, information can be altered by unauthorized users without detection. The ssl directive specifies whether to use TLS or not. If not specified it will default to no. It should be set to start_tls rather than doing LDAP over SSL. |
| R67 | Install the SSSD Package |
The sssd package should be installed.
The sssd package can be installed with the following command:
$ sudo yum install sssd |
|
| R67 | Configure SSSD LDAP Backend to Use TLS For All Transactions |
The LDAP client should be configured to implement TLS for the integrity
of all remote LDAP authentication sessions. If the id_provider is
set to ldap or ipa in /etc/sssd/sssd.conf or any of the
/etc/sssd/sssd.conf.d configuration files, ldap_id_use_start_tls
must be set to true.
To check if LDAP is configured to use TLS when id_provider is set to ldap or ipa, use the following command: $ sudo grep -i ldap_id_use_start_tls /etc/sssd/sssd.conf /etc/sssd/conf.d/*.conf |
Without cryptographic integrity protections, information can be altered by unauthorized users without detection. The ssl directive specifies whether to use TLS or not. If not specified it will default to no. It should be set to start_tls rather than doing LDAP over SSL. |
| R67 | Enable the SSSD Service |
The SSSD service should be enabled.
The sssd service can be enabled with the following command:
$ sudo systemctl enable sssd.service |
|
| R68 | Set number of Password Hashing Rounds - system-auth |
Configure the number or rounds for the password hashing algorithm. This can be
accomplished by using the rounds option for the pam_unix PAM module.
In file /etc/pam.d/system-auth append rounds=5000 to the pam_unix.so entry, as shown below: password sufficient pam_unix.so ...existing_options... rounds=5000The system's default number of rounds is 5000. |
Using a higher number of rounds makes password cracking attacks more difficult. |
| R68 | Ensure PAM Enforces Password Requirements - Minimum Different Categories |
The pam_pwquality module's minclass parameter controls
requirements for usage of different character classes, or types, of character
that must exist in a password before it is considered valid. For example,
setting this value to three (3) requires that any password must have characters
from at least three different categories in order to be approved. The default
value is zero (0), meaning there are no required classes. There are four
categories available:
* Upper-case characters * Lower-case characters * Digits * Special characters (for example, punctuation)Modify the minclass setting in /etc/security/pwquality.conf entry to require 3 differing categories of characters when changing passwords. |
Use of a complex password helps to increase the time and resources required to compromise the password.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts
at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised. Requiring a minimum number of character categories makes password guessing attacks more difficult by ensuring a larger search space. |
| R68 | Set number of Password Hashing Rounds - password-auth |
Configure the number or rounds for the password hashing algorithm. This can be
accomplished by using the rounds option for the pam_unix PAM module.
In file /etc/pam.d/password-auth append rounds=5000 to the pam_unix.so entry, as shown below: password sufficient pam_unix.so ...existing_options... rounds=5000The system's default number of rounds is 5000. |
Using a higher number of rounds makes password cracking attacks more difficult. |
| R68 | Set PAM''s Password Hashing Algorithm |
The PAM system service can be configured to only store encrypted
representations of passwords. In "/etc/pam.d/system-auth", the
password section of the file controls which PAM modules execute
during a password change. Set the pam_unix.so module in the
password section to include the argument sha512, as shown
below:
password sufficient pam_unix.so sha512 other arguments... This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default. |
Passwords need to be protected at all times, and encryption is the standard
method for protecting passwords. If passwords are not encrypted, they can
be plainly read (i.e., clear text) and easily compromised. Passwords that
are encrypted with a weak algorithm are no more protected than if they are
kepy in plain text.
This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult. |
| R68 | Ensure PAM Enforces Password Requirements - Authentication Retry Prompts Permitted Per-Session | To configure the number of retry prompts that are permitted per-session: Edit the /etc/security/pwquality.conf to include retry=3, or a lower value if site policy is more restrictive. The DoD requirement is a maximum of 3 prompts per session. | Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks. Note that this is different from account lockout, which is provided by the pam_faillock module. |
| R69 | Name Service Switch does not use NIS | Each call to a function which retrieves data from a system database like the password or group database is handled by the Name Service Switch implementation in the GNU C library. The various services provided are implemented by independent modules, each of which naturally varies widely from the other. One of such modules is the nis module, which allows to get information from NIS servers. | NIS service is insecure and should not be used. |
| R71 | Ensure Log Files Are Owned By Appropriate Group |
The group-owner of all log files written by
rsyslog should be root.
These log files are determined by the second part of each Rule line in
/etc/rsyslog.conf and typically all appear in /var/log.
For each log file LOGFILE referenced in /etc/rsyslog.conf,
run the following command to inspect the file's group owner:
$ ls -l LOGFILEIf the owner is not root, run the following command to correct this: $ sudo chgrp root LOGFILE |
The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access. |
| R71 | Ensure Logrotate Runs Periodically |
The logrotate utility allows for the automatic rotation of
log files. The frequency of rotation is specified in /etc/logrotate.conf,
which triggers a cron task or a timer. To configure logrotate to run daily, add or correct
the following line in /etc/logrotate.conf:
# rotate log files frequency daily |
Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full. |
| R71 | Ensure Logs Sent To Remote Host |
To configure rsyslog to send logs to a remote log server,
open /etc/rsyslog.conf and read and understand the last section of the file,
which describes the multiple directives necessary to activate remote
logging.
Along with these other directives, the system can be configured
to forward its logs to a particular log server by
adding or correcting one of the following lines,
substituting logcollector appropriately.
The choice of protocol depends on the environment of the system;
although TCP and RELP provide more reliable message delivery,
they may not be supported in all environments.
To use UDP for log message delivery: *.* @logcollector To use TCP for log message delivery: *.* @@logcollector To use RELP for log message delivery: *.* :omrelp:logcollector There must be a resolvable DNS CNAME or Alias record set to "logcollector" for logs to be sent correctly to the centralized logging utility. |
A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise. |
| R71 | The Chrony package is installed |
System time should be synchronized between all systems in an environment. This is
typically done by establishing an authoritative time server or set of servers and having all
systems synchronize their clocks to them.
The chrony package can be installed with the following command:
$ sudo yum install chrony |
Time synchronization is important to support time sensitive security mechanisms like Kerberos and also ensures log files have consistent time records across the enterprise, which aids in forensic investigations. |
| R71 | Enable the NTP Daemon |
Run the following command to determine the current status of the
chronyd service:
$ sudo systemctl is-active chronydIf the service is running, it should return the following: activeNote: The chronyd daemon is enabled by default. Run the following command to determine the current status of the ntpd service:
$ sudo systemctl is-active ntpdIf the service is running, it should return the following: activeNote: The ntpd daemon is not enabled by default. Though as mentioned in the previous sections in certain environments the ntpd daemon might be preferred to be used rather than the chronyd one. Refer to: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system_administrators_guide/ch-configuring_ntp_using_the_chrony_suite for guidance which NTP daemon to choose depending on the environment used. |
Enabling some of chronyd or ntpd services ensures
that the NTP daemon will be running and that the system will synchronize its
time to any servers specified. This is important whether the system is
configured to be a client (and synchronize only its own clock) or it is also
acting as an NTP server to other systems. Synchronizing time is essential for
authentication services such as Kerberos, but it is also important for
maintaining accurate logs and auditing possible security breaches.
The chronyd and ntpd NTP daemons offer all of the functionality of ntpdate, which is now deprecated. |
| R71 | Configure TLS for rsyslog remote logging |
Configure rsyslog to use Transport Layer
Security (TLS) support for logging to remote server
for the Forwarding Output Module in /etc/rsyslog.conf
using action. You can use the following command:
echo 'action(type="omfwd" protocol="tcp" Target="<remote system>" port="6514"
StreamDriver="gtls" StreamDriverMode="1" StreamDriverAuthMode="x509/name" streamdriver.CheckExtendedKeyPurpose="on")' >> /etc/rsyslog.conf
Replace the <remote system> in the above command with an IP address or a host name of the remote logging server.
|
For protection of data being logged, the connection to the remote logging server needs to be authenticated and encrypted. |
| R71 | Chrony Configure Pool and Server |
Chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to
synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on chrony can be found at
https://chrony-project.org/.
Chrony can be configured to be a client and/or a server.
Add or edit server or pool lines to /etc/chrony.conf as appropriate:
server <remote-server>Multiple servers may be configured. |
If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
| R71 | Ensure /var/log/audit Located On Separate Partition |
Audit logs are stored in the /var/log/audit directory.
Ensure that /var/log/audit has its own partition or logical
volume at installation time, or migrate it using LVM.
Make absolutely certain that it is large enough to store all
audit logs that will be created by the auditing daemon.
|
Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space. |
| R71 | A remote time server for Chrony is configured |
Chrony is a daemon which implements the Network Time Protocol (NTP). It is designed
to synchronize system clocks across a variety of systems and use a source that is highly
accurate. More information on chrony can be found at
https://chrony-project.org/.
Chrony can be configured to be a client and/or a server.
Add or edit server or pool lines to /etc/chrony.conf as appropriate:
server <remote-server>Multiple servers may be configured. |
If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly. |
| R71 | Ensure Log Files Are Owned By Appropriate User |
The owner of all log files written by
rsyslog should be
root.
These log files are determined by the second part of each Rule line in
/etc/rsyslog.conf and typically all appear in /var/log.
For each log file LOGFILE referenced in /etc/rsyslog.conf,
run the following command to inspect the file's owner:
$ ls -l LOGFILEIf the owner is not root, run the following command to correct this: $ sudo chown root LOGFILE |
The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access. |
| R71 | Ensure System Log Files Have Correct Permissions |
The file permissions for all log files written by rsyslog should
be set to 640, or more restrictive. These log files are determined by the
second part of each Rule line in /etc/rsyslog.conf and typically
all appear in /var/log. For each log file LOGFILE
referenced in /etc/rsyslog.conf, run the following command to
inspect the file's permissions:
$ ls -l LOGFILEIf the permissions are not 640 or more restrictive, run the following command to correct this: $ sudo chmod 640 LOGFILE" |
Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value. |
| R71 | Configure CA certificate for rsyslog remote logging |
Configure CA certificate for rsyslog logging
to remote server using Transport Layer Security (TLS)
using correct path for the DefaultNetstreamDriverCAFile
global option in /etc/rsyslog.conf, for example with the following command:
echo 'global(DefaultNetstreamDriverCAFile="/etc/pki/tls/cert.pem")' >> /etc/rsyslog.confReplace the /etc/pki/tls/cert.pem in the above command with the path to the file with CA certificate generated for the purpose of remote logging. |
The CA certificate needs to be set or rsyslog.service
fails to start with
error: ca certificate is not set, cannot continue |
| R71 | Ensure rsyslog-gnutls is installed |
TLS protocol support for rsyslog is installed.
The rsyslog-gnutls package can be installed with the following command:
$ sudo yum install rsyslog-gnutls |
The rsyslog-gnutls package provides Transport Layer Security (TLS) support for the rsyslog daemon, which enables secure remote logging. |
| R71 | Enable logrotate Timer |
The logrotate timer can be enabled with the following command:
$ sudo systemctl enable logrotate.timer |
Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full. |
| R71 | Ensure logrotate is Installed |
logrotate is installed by default. The logrotate package can be installed with the following command: $ sudo yum install logrotate |
The logrotate package provides the logrotate services. |
| R73 | Ensure auditd Collects Information on Kernel Module Loading and Unloading - finit_module |
If the auditd daemon is configured to use the augenrules program
to read audit rules during daemon startup (the default), add the following lines to a file
with suffix .rules in the directory /etc/audit/rules.d to capture kernel module
loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system:
-a always,exit -F arch=ARCH -S finit_module -F auid>=1000 -F auid!=unset -F key=modulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S finit_module -F auid>=1000 -F auid!=unset -F key=modules |
The addition/removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
| R73 | Record Attempts to perform maintenance activities |
The Red Hat Enterprise Linux 8 operating system must generate audit records for
privileged activities, nonlocal maintenance, diagnostic sessions and
other system-level access.
Verify the operating system audits activities performed during nonlocal
maintenance and diagnostic sessions. Run the following command:
$ sudo auditctl -l | grep sudo.log -w /var/log/sudo.log -p wa -k maintenance |
If events associated with nonlocal administrative access or diagnostic sessions are not logged, a major tool for assessing and investigating attacks would not be available. This requirement addresses auditing-related issues associated with maintenance tools used specifically for diagnostic and repair actions on organizational information systems. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. This requirement applies to hardware/software diagnostic test equipment or tools. This requirement does not cover hardware/software components that may support information system maintenance, yet are a part of the system, for example, the software implementing "ping," "ls," "ipconfig," or the hardware and software implementing the monitoring port of an Ethernet switch. |
| R73 | Record Attempts to Alter Logon and Logout Events - faillock |
The audit system already collects login information for all users
and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing logon events:
-w /var/log/faillock -p wa -k loginsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: -w /var/log/faillock -p wa -k logins |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fchown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Ensure auditd Collects Information on Kernel Module Loading - init_module |
To capture kernel module loading events, use following line, setting ARCH to
either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit:
-a always,exit -F arch=ARCH -S init_module -F auid>=1000 -F auid!=unset -F key=modulesPlace to add the line depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the line to a file with suffix .rules in the directory /etc/audit/rules.d. If the auditd daemon is configured to use the auditctl utility, add the line to file /etc/audit/audit.rules. |
The addition of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
| R73 | Ensure auditd Collects File Deletion Events by User - unlinkat |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
| R73 | Record attempts to alter time through adjtimex |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rulesIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rulesThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
| R73 | Record Events that Modify User/Group Information - /etc/gshadow |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/gshadow -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/gshadow -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - lsetxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S lsetxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S lsetxattr -F auid=0 -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S lsetxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S lsetxattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify the System's Mandatory Access Controls |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-w /etc/selinux/ -p wa -k MAC-policyIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/selinux/ -p wa -k MAC-policy |
The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited. |
| R73 | Ensure auditd Collects Information on the Use of Privileged Commands - modprobe |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/modprobe -p x -k modulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: -w /sbin/modprobe -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
| R73 | Ensure auditd Collects Information on the Use of Privileged Commands |
The audit system should collect information about usage of privileged commands for all users.
These are commands with suid or sgid bits on and they are specially risky in local block
device partitions not mounted with noexec and nosuid options. Therefore, these partitions
should be first identified by the following command:
findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,) | grep -Pv "noexec|nosuid"
For all partitions listed by the previous command, it is necessary to search for
setuid / setgid programs using the following command:
$ sudo find PARTITION -xdev -perm /6000 -type f 2>/dev/nullFor each setuid / setgid program identified by the previous command, an audit rule must be present in the appropriate place using the following line structure: -a always,exit -F path=PROG_PATH -F perm=x -F auid>=1000 -F auid!=unset -F key=privilegedIf the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup, add the line to a file with suffix .rules in the /etc/audit/rules.d directory, replacing the PROG_PATH part with the full path of that setuid / setgid identified program. If the auditd daemon is configured to use the auditctl utility instead, add the line to the /etc/audit/audit.rules file, also replacing the PROG_PATH part with the full path of that setuid / setgid identified program. |
Misuse of privileged functions, either intentionally or unintentionally by authorized users,
or by unauthorized external entities that have compromised system accounts, is a serious and
ongoing concern that can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify the
risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fchmodat |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Attempts to Alter the localtime File |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the default),
add the following line to a file with suffix .rules in the directory
/etc/audit/rules.d:
-w /etc/localtime -p wa -k audit_time_rulesIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/localtime -p wa -k audit_time_rulesThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used. |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - umount2 |
At a minimum, the audit system should collect file system umount2
changes. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S umount2 -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S umount2 -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S umount2 -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S umount2 -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Unsuccessful Access Attempts to Files - truncate |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
| R73 | Ensure auditd Collects Information on the Use of Privileged Commands - rmmod |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/rmmod -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
| R73 | Record Unsuccessful Access Attempts to Files - ftruncate |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
| R73 | Ensure auditd Collects File Deletion Events by User - renameat |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - removexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S removexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S removexattr -F auid=0 -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S removexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S removexattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - lchown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fchownat |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fremovexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S fremovexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S fremovexattr -F auid=0 -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S fremovexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S fremovexattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Attempts to Alter Time Through stime |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d for both 32 bit and 64 bit systems:
-a always,exit -F arch=b32 -S stime -F key=audit_time_rulesSince the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file for both 32 bit and 64 bit systems: -a always,exit -F arch=b32 -S stime -F key=audit_time_rulesSince the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined system calls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - chmod |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify User/Group Information - /etc/group |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/group -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/group -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
| R73 | Ensure auditd Collects Information on the Use of Privileged Commands - insmod |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-w /sbin/insmod -p x -k modules |
Misuse of privileged functions, either intentionally or unintentionally by
authorized users, or by unauthorized external entities that have compromised system accounts,
is a serious and ongoing concern and can have significant adverse impacts on organizations.
Auditing the use of privileged functions is one way to detect such misuse and identify
the risk from insider and advanced persistent threats.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity. |
| R73 | Ensure auditd Collects File Deletion Events by User - unlink |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
| R73 | Record Events that Modify the System's Network Environment |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification -w /etc/issue -p wa -k audit_rules_networkconfig_modification -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification -w /etc/hosts -p wa -k audit_rules_networkconfig_modification -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modificationIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification -w /etc/issue -p wa -k audit_rules_networkconfig_modification -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification -w /etc/hosts -p wa -k audit_rules_networkconfig_modification -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification |
The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited. |
| R73 | Record Unsuccessful Access Attempts to Files - openat |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
| R73 | Record Unsuccessful Access Attempts to Files - open |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
| R73 | Make the auditd Configuration Immutable |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d in order to make the auditd configuration
immutable:
-e 2If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file in order to make the auditd configuration immutable: -e 2With this setting, a reboot will be required to change any audit rules. |
Making the audit configuration immutable prevents accidental as well as malicious modification of the audit rules, although it may be problematic if legitimate changes are needed during system operation. |
| R73 | Ensure auditd Collects File Deletion Events by User - rename |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - setxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S setxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S setxattr -F auid=0 -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S setxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S setxattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify User/Group Information - /etc/passwd |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/passwd -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/passwd -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
| R73 | Ensure auditd Collects System Administrator Actions |
At a minimum, the audit system should collect administrator actions
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the default),
add the following line to a file with suffix .rules in the directory
/etc/audit/rules.d:
-w /etc/sudoers -p wa -k actions -w /etc/sudoers.d/ -p wa -k actionsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -w /etc/sudoers -p wa -k actions -w /etc/sudoers.d/ -p wa -k actions |
The actions taken by system administrators should be audited to keep a record of what was executed on the system, as well as, for accountability purposes. |
| R73 | Ensure auditd Collects Information on the Use of Privileged Commands - kmod |
At a minimum, the audit system should collect the execution of
privileged commands for all users and root. If the auditd daemon is
configured to use the augenrules program to read audit rules during
daemon startup (the default), add a line of the following form to a file with
suffix .rules in the directory /etc/audit/rules.d:
-a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=unset -F key=privilegedIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: -a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged |
Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the information system (e.g., module or policy filter). |
| R73 | Record Events that Modify the System's Discretionary Access Controls - chown |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify User/Group Information - /etc/security/opasswd |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
| R73 | Record Attempts to Alter Time Through clock_settime |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-changeIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-changeIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-changeIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-changeThe -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: -a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules |
Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited. |
| R73 | Record Attempts to Alter Logon and Logout Events - lastlog |
The audit system already collects login information for all users
and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing logon events:
-w /var/log/lastlog -p wa -k loginsIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: -w /var/log/lastlog -p wa -k logins |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fchmod |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Events that Modify User/Group Information - /etc/shadow |
If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d, in order to capture events that modify
account changes:
-w /etc/shadow -p wa -k audit_rules_usergroup_modification If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: -w /etc/shadow -p wa -k audit_rules_usergroup_modification |
In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy. |
| R73 | Record Unsuccessful Access Attempts to Files - creat |
At a minimum, the audit system should collect unauthorized file
accesses for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following lines to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=accessIf the system is 64 bit then also add the following lines: -a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access -a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access |
Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - fsetxattr |
At a minimum, the audit system should collect file permission
changes for all users and root. If the auditd daemon is configured
to use the augenrules program to read audit rules during daemon
startup (the default), add the following line to a file with suffix
.rules in the directory /etc/audit/rules.d:
-a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S fsetxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S fsetxattr -F auid=0 -F key=perm_modIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S fsetxattr -F auid=0 -F key=perm_modIf the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S fsetxattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Record Attempts to Alter Process and Session Initiation Information |
The audit system already collects process information for all
users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following lines to a file with suffix .rules in the
directory /etc/audit/rules.d in order to watch for attempted manual
edits of files involved in storing such process information:
-w /var/run/utmp -p wa -k session -w /var/log/btmp -p wa -k session -w /var/log/wtmp -p wa -k sessionIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for attempted manual edits of files involved in storing such process information: -w /var/run/utmp -p wa -k session -w /var/log/btmp -p wa -k session -w /var/log/wtmp -p wa -k session |
Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion. |
| R73 | Record Events that Modify the System's Discretionary Access Controls - lremovexattr |
At a minimum, the audit system should collect file permission
changes for all users and root.
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S lremovexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S lremovexattr -F auid=0 -F key=perm_mod If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b32 -S lremovexattr -F auid=0 -F key=perm_mod If the system is 64 bit then also add the following line: -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod -a always,exit -F arch=b64 -S lremovexattr -F auid=0 -F key=perm_mod |
The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users. |
| R73 | Ensure auditd Collects Information on Kernel Module Unloading - delete_module |
To capture kernel module unloading events, use following line, setting ARCH to
either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit:
-a always,exit -F arch=ARCH -S delete_module -F auid>=1000 -F auid!=unset -F key=modulesPlace to add the line depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the line to a file with suffix .rules in the directory /etc/audit/rules.d. If the auditd daemon is configured to use the auditctl utility, add the line to file /etc/audit/audit.rules. |
The removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel. |
| R73 | Ensure auditd Collects File Deletion Events by User - rmdir |
At a minimum, the audit system should collect file deletion events
for all users and root. If the auditd daemon is configured to use the
augenrules program to read audit rules during daemon startup (the
default), add the following line to a file with suffix .rules in the
directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S rmdir -F auid>=1000 -F auid!=unset -F key=deleteIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S rmdir -F auid>=1000 -F auid!=unset -F key=delete |
Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence. |
| R73 | Ensure auditd Collects Information on Exporting to Media (successful) |
At a minimum, the audit system should collect media exportation
events for all users and root. If the auditd daemon is configured to
use the augenrules program to read audit rules during daemon startup
(the default), add the following line to a file with suffix .rules in
the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as
appropriate for your system:
-a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=exportIf the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: -a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=export |
The unauthorized exportation of data to external media could result in an information leak where classified information, Privacy Act information, and intellectual property could be lost. An audit trail should be created each time a filesystem is mounted to help identify and guard against information loss. |
| R74 | Disable Postfix Network Listening |
Edit the file /etc/postfix/main.cf to ensure that only the following
inet_interfaces line appears:
inet_interfaces = loopback-only |
This ensures postfix accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack. |
| R75 | Configure System to Forward All Mail For The Root Account |
Make sure that mails delivered to root user are forwarded to a monitored
email address. Make sure that the address
change_me@localhost is a valid email address
reachable from the system in question. Use the following command to
configure the alias:
$ sudo echo "root: change_me@localhost" >> /etc/aliases $ sudo newaliases |
A number of system services utilize email messages sent to the root user to notify system administrators of active or impending issues. These messages must be forwarded to at least one monitored email address. |
| R76 | Configure Notification of Post-AIDE Scan Details |
AIDE should notify appropriate personnel of the details of a scan after the scan has been run.
If AIDE has already been configured for periodic execution in /etc/crontab, append the
following line to the existing AIDE line:
| /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhostOtherwise, add the following line to /etc/crontab: 05 4 * * * root /usr/sbin/aide --check | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhostAIDE can be executed periodically through other means; this is merely one example. |
Unauthorized changes to the baseline configuration could make the system vulnerable
to various attacks or allow unauthorized access to the operating system. Changes to
operating system configurations can have unintended side effects, some of which may
be relevant to security.
Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item. |
| R76 R79 |
Build and Test AIDE Database |
Run the following command to generate a new database:
$ sudo /usr/sbin/aide --initBy default, the database will be written to the file /var/lib/aide/aide.db.new.gz. Storing the database, the configuration file /etc/aide.conf, and the binary /usr/sbin/aide (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows: $ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gzTo initiate a manual check, run the following command: $ sudo /usr/sbin/aide --checkIf this check produces any unexpected output, investigate. |
For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files. |
| R76 | Configure AIDE to Verify Access Control Lists (ACLs) |
By default, the acl option is added to the FIPSR ruleset in AIDE.
If using a custom ruleset or the acl option is missing, add acl
to the appropriate ruleset.
For example, add acl to the following line in /etc/aide.conf:
FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. The remediation provided with this rule adds acl to all rule sets available in /etc/aide.conf |
ACLs can provide permissions beyond those permitted through the file mode and must be verified by the file integrity tools. |
| R76 | Configure Periodic Execution of AIDE |
At a minimum, AIDE should be configured to run a weekly scan.
To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab:
05 4 * * * root /usr/sbin/aide --checkTo implement a weekly execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 05 4 * * 0 root /usr/sbin/aide --checkAIDE can be executed periodically through other means; this is merely one example. The usage of cron's special time codes, such as @daily and @weekly is acceptable. |
By default, AIDE does not install itself for periodic execution. Periodically
running AIDE is necessary to reveal unexpected changes in installed files.
Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security. Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item. |
| R76 | Configure Systemd Timer Execution of AIDE |
At a minimum, AIDE should be configured to run a weekly scan.
To implement a systemd service and a timer unit to run the service periodically:
For example, if a systemd timer is expected to be started every day at 5AM
OnCalendar=*-*-* 05:00:0 [Timer]section in the timer unit and a Unit section starting the AIDE check service unit should be referred. |
AIDE provides a means to check if unauthorized changes are made to the system. AIDE itself does not setup a periodic execution, so in order to detect unauthorized changes a systemd service to run the check and a systemd timer to take care of periodical execution of that systemd service should be defined. |
| R76 R79 |
Install AIDE |
The aide package can be installed with the following command:
$ sudo yum install aide |
The AIDE package must be installed if it is to be available for integrity checking. |
| R76 | Configure AIDE to Verify Extended Attributes |
By default, the xattrs option is added to the FIPSR ruleset in AIDE.
If using a custom ruleset or the xattrs option is missing, add xattrs
to the appropriate ruleset.
For example, add xattrs to the following line in /etc/aide.conf:
FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. The remediation provided with this rule adds xattrs to all rule sets available in /etc/aide.conf |
Extended attributes in file systems are used to contain arbitrary data and file metadata with security implications. |