To capture kernel module loading and unloading events, use following lines, 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,finit_module,delete_module -F auid>=1000 -F auid!=unset -F key=modulesThe place to add the lines depends on a way auditd daemon is configured. If it is configured to use the augenrules program (the default), add the lines 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 lines to file /etc/audit/audit.rules.
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.
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 create_module -F key=module-changePlace 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.
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.
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.
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.
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 query_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 query_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.
To improve the kernel capacity to queue all log events, even those which occurred prior to the audit daemon, add the argument audit_backlog_limit=8192 to all BLS (Boot Loader Specification) entries ('options' line) for the Linux operating system in /boot/loader/entries/*.conf.
audit_backlog_limit sets the queue length for audit events awaiting transfer to the audit daemon. Until the audit daemon is up and running, all log messages are stored in this queue. If the queue is overrun during boot process, the action defined by audit failure flag is taken.
SELinux can be disabled at boot time by disabling it via a kernel argument. Remove any instances of selinux=0 from the kernel arguments in that file to prevent SELinux from being disabled at boot.
Disabling a major host protection feature, such as SELinux, at boot time prevents it from confining system services at boot time. Further, it increases the chances that it will remain off during system operation.
All USB support can be disabled by adding the nousb argument to the kernel's boot loader configuration. To do so, Add the nousb kernel argument via a MachineConfig object.
Disabling the USB subsystem within the Linux kernel at system boot will protect against potentially malicious USB devices, although it is only practical in specialized systems.
To enable poisoning of free pages, add the argument page_poison=1 to all BLS (Boot Loader Specification) entries ('options' line) for the Linux operating system in /boot/loader/entries/*.conf.
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.
To enable Kernel page-table isolation, add the argument pti=on to all BLS (Boot Loader Specification) entries ('options' line) for the Linux operating system in /boot/loader/entries/*.conf.
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).
To enable poisoning of SLUB/SLAB objects, add the argument slub_debug=P to all BLS (Boot Loader Specification) entries ('options' line) for the Linux operating system in /boot/loader/entries/*.conf.
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.
To disable use of virtual syscalls, add the argument vsyscall=none to all BLS (Boot Loader Specification) entries ('options' line) for the Linux operating system in /boot/loader/entries/*.conf.
Virtual Syscalls provide an opportunity of attack for a user who has control of the return instruction pointer.
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.
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.
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.
To disable IPv6 protocol support in the Linux kernel, add the argument ipv6.disable=1 to the default GRUB2 command line for the Linux operating system. To ensure that ipv6.disable=1 is added as a kernel command line argument to newly installed kernels, add ipv6.disable=1 to the default Grub2 command line for Linux operating systems. Modify the line within /etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... ipv6.disable=1 ..."Run the following command to update command line for already installed kernels:
# grubby --update-kernel=ALL --args="ipv6.disable=1"
Any unnecessary network stacks, including IPv6, should be disabled to reduce the vulnerability to exploitation.
There exist two ways how to ensure that the Linux kernel trusts the CPU hardware random number generator. If the option is configured during kernel compilation, e.g. the option CONFIG_RANDOM_TRUST_CPU is set to Y, make sure that it is not overridden with the boot parameter. There must not exist the boot parameter random.trust_cpu=off. If the option is not compiled in, make sure that random.trust_cpu=on is configured as a boot parameter. To ensure that random.trust_cpu=on is added as a kernel command line argument to newly installed kernels, add random.trust_cpu=on to the default Grub2 command line for Linux operating systems. Modify the line within /etc/default/grub as shown below:
GRUB_CMDLINE_LINUX="... random.trust_cpu=on ..."Run the following command to update command line for already installed kernels:
# grubby --update-kernel=ALL --args="random.trust_cpu=on"
The Linux kernel offers an option which signifies if the kernel should trust data provided by CPU hardware random number generator. Hardware random number generators can provide random data very quickly and are used to generate random cryptographic keys. They can be useful during boot time when other means of getting random data can be slow because there is not yet enough entropy in the system.
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 dnf 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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Disable support for IP version 6 (IPv6). The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_IPV6, run the following command: grep CONFIG_IPV6 /boot/config-* Configs with value 'n' are not explicitly set in the file, so either commented lines or no lines should be returned.
Any unnecessary network stacks, including IPv6, should be disabled to reduce the vulnerability to exploitation.
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.
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.
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.
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.
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.
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.
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.
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.
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.
This configures the kernel to build and sign modules using $var_kernel_config_module_sig_hash as the hash function. The configuration that was used to build kernel is available at /boot/config-*. To check the configuration value for CONFIG_MODULE_SIG_HASH, run the following command: grep CONFIG_MODULE_SIG_HASH /boot/config-* For each kernel installed, a line with value "$var_kernel_config_module_sig_hash" should be returned.
Use of strong hash function is important to secure the module against counterfeit signatures.
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 "$var_kernel_config_module_sig_key" should be returned.
A key and certificate is required to sign the built 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_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.
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.
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.
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.
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.
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.
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 "$var_kernel_config_panic_timeout" should be returned.
This is required to enable protection against Spectre v2.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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)
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)
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.
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.
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.
For each solid-state drive on the system, run:
# echo 0 > /sys/block/DRIVE/queue/add_random
In contrast to traditional electromechanical magnetic disks, containing spinning disks and / or movable read / write heads, the solid-state storage devices (SSDs) do not contain moving / mechanical components. Therefore the I/O operation completion times are much more predictable for them.
The Asynchronous Transfer Mode (ATM) is a protocol operating on
network, data link, and physical layers, based on virtual circuits
and virtual paths.
To configure the system to prevent the atm
kernel module from being loaded, add the following line to the file /etc/modprobe.d/atm.conf:
install atm /bin/false
Disabling ATM protects the system against exploitation of any flaws in its implementation.
The kernel's module loading system can be configured to prevent loading of the Bluetooth module. Add the following to the appropriate /etc/modprobe.d configuration file to prevent the loading of the Bluetooth module:
install bluetooth /bin/true
If Bluetooth functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
The Controller Area Network (CAN) is a serial communications
protocol which was initially developed for automotive and
is now also used in marine, industrial, and medical applications.
To configure the system to prevent the can
kernel module from being loaded, add the following line to the file /etc/modprobe.d/can.conf:
install can /bin/false
Disabling CAN protects the system against exploitation of any flaws in its implementation.
To configure the system to prevent the cfg80211
kernel module from being loaded, add the following line to the file /etc/modprobe.d/cfg80211.conf:
install cfg80211 /bin/false
If Wireless functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
To configure the system to prevent the cramfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/cramfs.conf:
install cramfs /bin/falseThis effectively prevents usage of this uncommon filesystem. The cramfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems. A cramfs image can be used without having to first decompress the image.
Removing support for unneeded filesystem types reduces the local attack surface of the server.
The Datagram Congestion Control Protocol (DCCP) is a
relatively new transport layer protocol, designed to support
streaming media and telephony.
To configure the system to prevent the dccp
kernel module from being loaded, add the following line to the file /etc/modprobe.d/dccp.conf:
install dccp /bin/false
Disabling DCCP protects the system against exploitation of any flaws in its implementation.
The IEEE 1394 (FireWire) is a serial bus standard for
high-speed real-time communication.
To configure the system to prevent the firewire-core
kernel module from being loaded, add the following line to the file /etc/modprobe.d/firewire-core.conf:
install firewire-core /bin/false
Disabling FireWire protects the system against exploitation of any flaws in its implementation.
To configure the system to prevent the freevxfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/freevxfs.conf:
install freevxfs /bin/falseThis effectively prevents usage of this uncommon filesystem.
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
To configure the system to prevent the hfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/hfs.conf:
install hfs /bin/falseThis effectively prevents usage of this uncommon filesystem.
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
To configure the system to prevent the hfsplus
kernel module from being loaded, add the following line to the file /etc/modprobe.d/hfsplus.conf:
install hfsplus /bin/falseThis effectively prevents usage of this uncommon filesystem.
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
To prevent the IPv6 kernel module (ipv6) from binding to the IPv6 networking stack, add the following line to /etc/modprobe.d/disabled.conf (or another file in /etc/modprobe.d):
options ipv6 disable=1This permits the IPv6 module to be loaded (and thus satisfy other modules that depend on it), while disabling support for the IPv6 protocol.
Any unnecessary network stacks - including IPv6 - should be disabled, to reduce the vulnerability to exploitation.
To configure the system to prevent the iwlmvm
kernel module from being loaded, add the following line to the file /etc/modprobe.d/iwlmvm.conf:
install iwlmvm /bin/false
If Wireless functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
To configure the system to prevent the iwlwifi
kernel module from being loaded, add the following line to the file /etc/modprobe.d/iwlwifi.conf:
install iwlwifi /bin/false
If Wireless functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
To configure the system to prevent the jffs2
kernel module from being loaded, add the following line to the file /etc/modprobe.d/jffs2.conf:
install jffs2 /bin/falseThis effectively prevents usage of this uncommon filesystem.
Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
To configure the system to prevent the mac80211
kernel module from being loaded, add the following line to the file /etc/modprobe.d/mac80211.conf:
install mac80211 /bin/false
If Wireless functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.
The Reliable Datagram Sockets (RDS) protocol is a transport
layer protocol designed to provide reliable high-bandwidth,
low-latency communications between nodes in a cluster.
To configure the system to prevent the rds
kernel module from being loaded, add the following line to the file /etc/modprobe.d/rds.conf:
install rds /bin/false
Disabling RDS protects the system against exploitation of any flaws in its implementation.
The Stream Control Transmission Protocol (SCTP) is a
transport layer protocol, designed to support the idea of
message-oriented communication, with several streams of messages
within one connection.
To configure the system to prevent the sctp
kernel module from being loaded, add the following line to the file /etc/modprobe.d/sctp.conf:
install sctp /bin/false
Disabling SCTP protects the system against exploitation of any flaws in its implementation.
To configure the system to prevent the squashfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/squashfs.conf:
install squashfs /bin/falseThis effectively prevents usage of this uncommon filesystem. The squashfs filesystem type is a compressed read-only Linux filesystem embedded in small footprint systems (similar to cramfs). A squashfs image can be used without having to first decompress the image.
Removing support for unneeded filesystem types reduces the local attack surface of the system.
The Transparent Inter-Process Communication (TIPC) protocol
is designed to provide communications between nodes in a
cluster.
To configure the system to prevent the tipc
kernel module from being loaded, add the following line to the file /etc/modprobe.d/tipc.conf:
install tipc /bin/false
Disabling TIPC protects the system against exploitation of any flaws in its implementation.
To configure the system to prevent the udf
kernel module from being loaded, add the following line to the file /etc/modprobe.d/udf.conf:
install udf /bin/falseThis effectively prevents usage of this uncommon filesystem. The udf filesystem type is the universal disk format used to implement the ISO/IEC 13346 and ECMA-167 specifications. This is an open vendor filesystem type for data storage on a broad range of media. This filesystem type is neccessary to support writing DVDs and newer optical disc formats.
Removing support for unneeded filesystem types reduces the local attack surface of the system.
To prevent USB storage devices from being used, configure the kernel module loading system
to prevent automatic loading of the USB storage driver.
To configure the system to prevent the usb-storage
kernel module from being loaded, add the following line to the file /etc/modprobe.d/usb-storage.conf:
install usb-storage /bin/falseThis will prevent the modprobe program from loading the usb-storage module, but will not prevent an administrator (or another program) from using the insmod program to load the module manually.
USB storage devices such as thumb drives can be used to introduce malicious software.
If the device contains a camera it should be covered or disabled when not in use.
Failing to disconnect from collaborative computing devices (i.e., cameras) can result in subsequent compromises of organizational information. Providing easy methods to physically disconnect from such devices after a collaborative computing session helps to ensure participants actually carry out the disconnect activity without having to go through complex and tedious procedures.
To configure the system to prevent the vfat
kernel module from being loaded, add the following line to the file /etc/modprobe.d/vfat.conf:
install vfat /bin/falseThis effectively prevents usage of this uncommon filesystem. The vFAT filesystem format is primarily used on older windows systems and portable USB drives or flash modules. It comes in three types FAT12, FAT16, and FAT32 all of which are supported by the vfat kernel module.
Removing support for unneeded filesystems reduces the local attack surface of the system.
Edit the file /etc/sysconfig/network-scripts/ifcfg-interface, and add or correct the following line (substituting your gateway IP as appropriate):
IPV6_DEFAULTGW=2001:0DB8::0001Router addresses should be manually set and not accepted via any auto-configuration or router advertisement.
To disable interface usage of IPv6, add or correct the following lines in /etc/sysconfig/network:
NETWORKING_IPV6=no IPV6INIT=no
RPC services for NFSv4 try to load transport modules for udp6 and tcp6 by default, even if IPv6 has been disabled in /etc/modprobe.d. To prevent RPC services such as rpc.mountd from attempting to start IPv6 network listeners, remove or comment out the following two lines in /etc/netconfig:
udp6 tpi_clts v inet6 udp - - tcp6 tpi_cots_ord v inet6 tcp - -
To introduce randomness into the automatic generation of IPv6 addresses, add or correct the following line in /etc/sysconfig/network-scripts/ifcfg-interface:
IPV6_PRIVACY=rfc3041Automatically-generated IPv6 addresses are based on the underlying hardware (e.g. Ethernet) address, and so it becomes possible to track a piece of hardware over its lifetime using its traffic. If it is important for a system's IP address to not trivially reveal its hardware address, this setting should be applied.
To manually assign an IP address for an interface, edit the file /etc/sysconfig/network-scripts/ifcfg-interface. Add or correct the following line (substituting the correct IPv6 address):
IPV6ADDR=2001:0DB8::ABCD/64Manually assigning an IP address is preferable to accepting one from routers or from the network otherwise. The example address here is an IPv6 address reserved for documentation purposes, as defined by RFC3849.
The abrt-addon-kerneloops package can be removed with the following command:
$ sudo dnf remove abrt-addon-kerneloops
abrt-addon-kerneloops contains plugins for collecting kernel crash information and reporter plugin which sends this information to a specified server, usually to kerneloops.org.
The iptables-nft package can be installed with the following command:
$ sudo dnf install iptables-nft
iptables-nft controls the Linux kernel network packet filtering code. iptables-nft allows system operators to set up firewalls and IP masquerading, etc.
The nfs-kernel-server package can be removed with the following command:
$ sudo dnf remove nfs-kernel-server
If the system does not export NFS shares or act as an NFS client, it is recommended that these services be removed to reduce the remote attack surface.
By default, the SELinux boolean domain_kernel_load_modules is disabled.
If this setting is enabled, it should be disabled.
To disable the domain_kernel_load_modules SELinux boolean, run the following command:
$ sudo setsebool -P domain_kernel_load_modules off
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.
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().
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.
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().
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.
To set the runtime status of the kernel.core_pattern kernel parameter, run the following command:
$ sudo sysctl -w kernel.core_pattern=|/bin/falseTo make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.core_pattern = |/bin/false
A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers trying to debug problems.
The kernel.core_pattern option specifies the core dumpfile pattern
name. It can be set to an empty string. In this case, the kernel
behaves differently based on another related option. If
kernel.core_uses_pid is set to 1, then a file named as
.PID (where PID is process ID of the crashed process) is
created in the working directory. If kernel.core_uses_pid is set to
0, no coredump is saved.
To set the runtime status of the kernel.core_pattern kernel parameter,
run the following command:
$ sudo sysctl -w kernel.core_pattern=To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.core_pattern =
A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers trying to debug problems.
To set the runtime status of the kernel.core_uses_pid kernel parameter, run the following command:
$ sudo sysctl -w kernel.core_uses_pid=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.core_uses_pid = 0
The default coredump filename is core. By setting core_uses_pid to 1, the coredump filename becomes core.PID. If core_pattern does not include %p (default does not) and core_uses_pid is set, then .PID will be appended to the filename. When combined with kernel.core_pattern = "" configuration, it is ensured that no core dumps are generated and also no confusing error messages are printed by a shell.
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.
By default on Red Hat Enterprise Linux 9 64-bit systems, ExecShield is enabled and can only be disabled if the hardware does not support ExecShield or is disabled in /etc/default/grub.
ExecShield uses the segmentation feature on all x86 systems to prevent execution in memory higher than a certain address. It writes an address as a limit in the code segment descriptor, to control where code can be executed, on a per-process basis. When the kernel places a process's memory regions such as the stack and heap higher than this address, the hardware prevents execution in that address range. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware.
To set the runtime status of the kernel.kexec_load_disabled kernel parameter, run the following command:
$ sudo sysctl -w kernel.kexec_load_disabled=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.kexec_load_disabled = 1
Disabling kexec_load allows greater control of the kernel memory. It makes it impossible to load another kernel image after it has been disabled.
To set the runtime status of the kernel.kptr_restrict kernel parameter, run the following command:
$ sudo sysctl -w kernel.kptr_restrict=$sysctl_kernel_kptr_restrict_valueTo make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.kptr_restrict = $sysctl_kernel_kptr_restrict_value
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
To prevent unprivileged processes from using the bpf() syscall
the kernel.unprivileged_bpf_disabled kernel parameter must
be set to 1 or 2.
Writing 1 to this entry will disable unprivileged calls to bpf(); once
disabled, calling bpf() without CAP_SYS_ADMIN or CAP_BPF will return -EPERM.
Once set to 1, this can't be cleared from the running kernel anymore.
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 = 1Writing
2 to this entry will also disable unprivileged calls to bpf(),
however, an admin can still change this setting later on, if needed, by
writing 0 or 1 to this entry.
To set the runtime status of the kernel.unprivileged_bpf_disabled kernel parameter,
run the following command:
$ sudo sysctl -w kernel.unprivileged_bpf_disabled=2To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
kernel.unprivileged_bpf_disabled = 2
Loading and accessing the packet filters programs and maps using the bpf() syscall has the potential of revealing sensitive information about the kernel state.
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).
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.
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.
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."
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.
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=$sysctl_net_ipv4_conf_all_arp_filter_valueTo 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 = $sysctl_net_ipv4_conf_all_arp_filter_value
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.
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=$sysctl_net_ipv4_conf_all_arp_ignore_valueTo 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 = $sysctl_net_ipv4_conf_all_arp_ignore_value
Avoids ARP Flux on system that have more than one interface on the same subnet.
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.
To set the runtime status of the net.ipv4.conf.all.forwarding kernel parameter, run the following command:
$ sudo sysctl -w net.ipv4.conf.all.forwarding=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.forwarding = 0
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers.
To set the runtime status of the net.ipv4.conf.all.log_martians kernel parameter, run the following command:
$ sudo sysctl -w net.ipv4.conf.all.log_martians=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.log_martians = 1
The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected.
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.
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.
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.
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.
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.
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.
To set the runtime status of the net.ipv4.conf.default.log_martians kernel parameter, run the following command:
$ sudo sysctl -w net.ipv4.conf.default.log_martians=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.log_martians = 1
The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected.
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.
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.
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.
To set the runtime status of the net.ipv4.icmp_echo_ignore_broadcasts kernel parameter, run the following command:
$ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
net.ipv4.icmp_echo_ignore_broadcasts = 1
Responding to broadcast (ICMP) echoes facilitates network mapping
and provides a vector for amplification attacks.
Ignoring ICMP echo requests (pings) sent to broadcast or multicast
addresses makes the system slightly more difficult to enumerate on the network.
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.
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.
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.
Make sure that the system is configured to limit the maximal rate for sending duplicate acknowledgments in response to incoming TCP packets that are for an existing connection but that are invalid due to any of these reasons: (a) out-of-window sequence number, (b) out-of-window acknowledgment number, or (c) PAWS (Protection Against Wrapped Sequence numbers) check failure This measure protects against or limits effects of DoS attacks against the system. Set the system to implement rate-limiting measures by adding the following line to /etc/sysctl.conf or a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value):
net.ipv4.tcp_invalid_ratelimit = $sysctl_net_ipv4_tcp_invalid_ratelimit_valueIssue the following command to make the changes take effect:
# sysctl --system
Denial of Service (DoS) is a condition when a resource is not available for legitimate users. When
this occurs, the organization either cannot accomplish its mission or must
operate at degraded capacity.
This can help mitigate simple “ack loop” DoS attacks, wherein a buggy or
malicious middlebox or man-in-the-middle can rewrite TCP header fields in
manner that causes each endpoint to think that the other is sending invalid
TCP segments, thus causing each side to send an unterminating stream of
duplicate acknowledgments for invalid segments.
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.
To set the runtime status of the net.ipv6.conf.all.accept_ra kernel parameter, run the following command:
$ sudo sysctl -w net.ipv6.conf.all.accept_ra=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 = 0
An illicit router advertisement message could result in a man-in-the-middle attack.
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.
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.
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.
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.
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.
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.
To disable support for (ipv6) addressing on all interface add the following line to /etc/sysctl.d/ipv6.conf (or another file in /etc/sysctl.d):
net.ipv6.conf.all.disable_ipv6 = 1This disables IPv6 on all network interfaces as other services and system functionality require the IPv6 stack loaded to work.
Any unnecessary network stacks - including IPv6 - should be disabled, to reduce the vulnerability to exploitation.
To set the runtime status of the net.ipv6.conf.all.forwarding kernel parameter, run the following command:
$ sudo sysctl -w net.ipv6.conf.all.forwarding=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.forwarding = 0
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers.
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.
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.
To set the runtime status of the net.ipv6.conf.default.accept_ra kernel parameter, run the following command:
$ sudo sysctl -w net.ipv6.conf.default.accept_ra=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 = 0
An illicit router advertisement message could result in a man-in-the-middle attack.
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.
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.
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.
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.
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.
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.
To disable support for (ipv6) addressing on interfaces by default add the following line to /etc/sysctl.d/ipv6.conf (or another file in /etc/sysctl.d):
net.ipv6.conf.default.disable_ipv6 = 1This disables IPv6 on network interfaces by default as other services and system functionality require the IPv6 stack loaded to work.
Any unnecessary network stacks - including IPv6 - should be disabled, to reduce the vulnerability to exploitation.
To set the runtime status of the net.ipv6.conf.default.forwarding kernel parameter, run the following command:
$ sudo sysctl -w net.ipv6.conf.default.forwarding=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.forwarding = 0
IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers.
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.
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.
To set the runtime status of the user.max_user_namespaces kernel parameter,
run the following command:
$ sudo sysctl -w user.max_user_namespaces=0To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:
user.max_user_namespaces = 0When containers are deployed on the machine, the value should be set to large non-zero value.
It is detrimental for operating systems to provide, or install by default, functionality exceeding requirements or system objectives. These unnecessary capabilities or services are often overlooked and therefore may remain unsecured. They increase the risk to the platform by providing additional attack vectors. User namespaces are used primarily for Linux containers. The value 0 disallows the use of user namespaces.
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.