Rules with CIS Reference in Guide to the Secure Configuration of Red Hat Enterprise Linux 8


Mapping Rule Title Description Rationale
1.1.1.1 Disable Mounting of cramfs 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/false
To configure the system to prevent the cramfs from being used, add the following line to file /etc/modprobe.d/cramfs.conf: 
blacklist cramfs
This 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.
1.1.1.2 Disable Mounting of freevxfs 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/false
To configure the system to prevent the freevxfs from being used, add the following line to file /etc/modprobe.d/freevxfs.conf: 
blacklist freevxfs
This effectively prevents usage of this uncommon filesystem. 		Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
1.1.1.3 Disable Mounting of hfs 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/false
To configure the system to prevent the hfs from being used, add the following line to file /etc/modprobe.d/hfs.conf: 
blacklist hfs
This effectively prevents usage of this uncommon filesystem. 		Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
1.1.1.4 Disable Mounting of hfsplus 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/false
To configure the system to prevent the hfsplus from being used, add the following line to file /etc/modprobe.d/hfsplus.conf: 
blacklist hfsplus
This effectively prevents usage of this uncommon filesystem. 		Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
1.1.1.5 Disable Mounting of jffs2 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/false
To configure the system to prevent the jffs2 from being used, add the following line to file /etc/modprobe.d/jffs2.conf: 
blacklist jffs2
This effectively prevents usage of this uncommon filesystem. 		Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.
1.1.1.6 Disable Mounting of squashfs 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/false
To configure the system to prevent the squashfs from being used, add the following line to file /etc/modprobe.d/squashfs.conf: 
blacklist squashfs
This 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.
1.1.1.7 Disable Mounting of udf 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/false
To configure the system to prevent the udf from being used, add the following line to file /etc/modprobe.d/udf.conf: 
blacklist udf
This 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.
1.1.1.8 Disable Modprobe Loading of USB Storage Driver 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/false
To configure the system to prevent the usb-storage from being used, add the following line to file /etc/modprobe.d/usb-storage.conf: 
blacklist usb-storage
This 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.
1.1.2.1.1 Ensure /tmp Located On Separate Partition The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.
1.1.2.1.2 Add nodev Option to /tmp The nodev mount option can be used to prevent device files from being created in /tmp. Legitimate character and block devices should not exist within temporary directories like /tmp. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.1.3 Add nosuid Option to /tmp The nosuid mount option can be used to prevent execution of setuid programs in /tmp. The SUID and SGID permissions should not be required in these world-writable directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.
1.1.2.1.4 Add noexec Option to /tmp The noexec mount option can be used to prevent binaries from being executed out of /tmp. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /tmp. Allowing users to execute binaries from world-writable directories such as /tmp should never be necessary in normal operation and can expose the system to potential compromise.
1.1.2.2.1 Ensure /dev/shm is configured The /dev/shm is a traditional shared memory concept. One program will create a memory portion, which other processes (if permitted) can access. If /dev/shm is not configured, tmpfs will be mounted to /dev/shm by systemd. Any user can upload and execute files inside the /dev/shm similar to the /tmp partition. Configuring /dev/shm allows an administrator to set the noexec option on the mount, making /dev/shm useless for an attacker to install executable code. It would also prevent an attacker from establishing a hardlink to a system setuid program and wait for it to be updated. Once the program was updated, the hardlink would be broken and the attacker would have his own copy of the program. If the program happened to have a security vulnerability, the attacker could continue to exploit the known flaw.
1.1.2.2.2 Add nodev Option to /dev/shm The nodev mount option can be used to prevent creation of device files in /dev/shm. Legitimate character and block devices should not exist within temporary directories like /dev/shm. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /dev/shm. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.2.3 Add nosuid Option to /dev/shm The nosuid mount option can be used to prevent execution of setuid programs in /dev/shm. The SUID and SGID permissions should not be required in these world-writable directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /dev/shm. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.
1.1.2.2.4 Add noexec Option to /dev/shm The noexec mount option can be used to prevent binaries from being executed out of /dev/shm. It can be dangerous to allow the execution of binaries from world-writable temporary storage directories such as /dev/shm. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /dev/shm. Allowing users to execute binaries from world-writable directories such as /dev/shm can expose the system to potential compromise.
1.1.2.3.1 Ensure /home Located On Separate Partition If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later. Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.
1.1.2.3.2 Add nodev Option to /home The nodev mount option can be used to prevent device files from being created in /home. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /home. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.3.3 Add nosuid Option to /home The nosuid mount option can be used to prevent execution of setuid programs in /home. The SUID and SGID permissions should not be required in these user data directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /home. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from user home directory partitions.
1.1.2.4.1 Ensure /var Located On Separate Partition The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM. Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages.
1.1.2.4.2 Add nodev Option to /var The nodev mount option can be used to prevent device files from being created in /var. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /var. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.4.3 Add nosuid Option to /var The nosuid mount option can be used to prevent execution of setuid programs in /var. The SUID and SGID permissions should not be required for this directory. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var. The presence of SUID and SGID executables should be tightly controlled.
1.1.2.5.1 Ensure /var/tmp Located On Separate Partition The /var/tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM. The /var/tmp partition is used as temporary storage by many programs. Placing /var/tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.
1.1.2.5.2 Add nodev Option to /var/tmp The nodev mount option can be used to prevent device files from being created in /var/tmp. Legitimate character and block devices should not exist within temporary directories like /var/tmp. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.5.3 Add nosuid Option to /var/tmp The nosuid mount option can be used to prevent execution of setuid programs in /var/tmp. The SUID and SGID permissions should not be required in these world-writable directories. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.
1.1.2.6.1 Ensure /var/log Located On Separate Partition System logs are stored in the /var/log directory. Ensure that /var/log has its own partition or logical volume at installation time, or migrate it using LVM. Placing /var/log in its own partition enables better separation between log files and other files in /var/.
1.1.2.6.2 Add nodev Option to /var/log The nodev mount option can be used to prevent device files from being created in /var/log. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /var/log. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.6.3 Add nosuid Option to /var/log The nosuid mount option can be used to prevent execution of setuid programs in /var/log. The SUID and SGID permissions should not be required in directories containing log files. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var/log. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from partitions designated for log files.
1.1.2.6.4 Add noexec Option to /var/log The noexec mount option can be used to prevent binaries from being executed out of /var/log. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/log. Allowing users to execute binaries from directories containing log files such as /var/log should never be necessary in normal operation and can expose the system to potential compromise.
1.1.2.7.1 Ensure /var/log/audit Located On Separate Partition Audit logs are stored in the /var/log/audit directory. Ensure that /var/log/audit has its own partition or logical volume at installation time, or migrate it using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon. Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.
1.1.2.7.2 Add nodev Option to /var/log/audit The nodev mount option can be used to prevent device files from being created in /var/log/audit. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of /var/log/audit. The only legitimate location for device files is the /dev directory located on the root partition. The only exception to this is chroot jails.
1.1.2.7.3 Add nosuid Option to /var/log/audit The nosuid mount option can be used to prevent execution of setuid programs in /var/log/audit. The SUID and SGID permissions should not be required in directories containing audit log files. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of /var/log/audit. The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from partitions designated for audit log files.
1.1.2.7.4 Add noexec Option to /var/log/audit The noexec mount option can be used to prevent binaries from being executed out of /var/log/audit. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/log/audit. Allowing users to execute binaries from directories containing audit log files such as /var/log/audit should never be necessary in normal operation and can expose the system to potential compromise.
1.1.3.5.4 Add noexec Option to /var/tmp The noexec mount option can be used to prevent binaries from being executed out of /var/tmp. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp. Allowing users to execute binaries from world-writable directories such as /var/tmp should never be necessary in normal operation and can expose the system to potential compromise.
1.2.2 Ensure gpgcheck Enabled In Main yum Configuration The gpgcheck option controls whether RPM packages' signatures are always checked prior to installation. To configure yum to check package signatures before installing them, ensure the following line appears in /etc/yum.conf in the [main] section: 
gpgcheck=1
 Changes to any software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).
1.2.2 Ensure gpgcheck Enabled for All yum Package Repositories To ensure signature checking is not disabled for any repos, remove any lines from files in /etc/yum.repos.d of the form: 
gpgcheck=0
 Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA)."
1.3.1 Set the UEFI Boot Loader Password The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

Since plaintext passwords are a security risk, generate a hash for the password by running the following command: 
# grub2-setpassword
When prompted, enter the password that was selected.

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode.
1.3.1 Set Boot Loader Password in grub2 The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

Since plaintext passwords are a security risk, generate a hash for the password by running the following command: 
# grub2-setpassword
When prompted, enter the password that was selected.

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode.
1.3.2 Verify /boot/grub2/user.cfg Permissions File permissions for /boot/grub2/user.cfg should be set to 600. To properly set the permissions of /boot/grub2/user.cfg, run the command: 
$ sudo chmod 600 /boot/grub2/user.cfg
 Proper permissions ensure that only the root user can read or modify important boot parameters.
1.3.2 Verify /boot/grub2/user.cfg Group Ownership The file /boot/grub2/user.cfg should be group-owned by the root group to prevent reading or modification of the file. To properly set the group owner of /boot/grub2/user.cfg, run the command: 
$ sudo chgrp root /boot/grub2/user.cfg
 The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them.
1.3.2 Verify /boot/grub2/grub.cfg User Ownership The file /boot/grub2/grub.cfg should be owned by the root user to prevent destruction or modification of the file. To properly set the owner of /boot/grub2/grub.cfg, run the command: 
$ sudo chown root /boot/grub2/grub.cfg
Only root should be able to modify important boot parameters.
1.3.2 Verify the UEFI Boot Loader grub.cfg Group Ownership The file /boot/efi/EFI/redhat/grub.cfg should be group-owned by the root group to prevent destruction or modification of the file. To properly set the group owner of /boot/efi/EFI/redhat/grub.cfg, run the command: 
$ sudo chgrp root /boot/efi/EFI/redhat/grub.cfg
 The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.
1.3.2 Verify /boot/grub2/grub.cfg Group Ownership The file /boot/grub2/grub.cfg should be group-owned by the root group to prevent destruction or modification of the file. To properly set the group owner of /boot/grub2/grub.cfg, run the command: 
$ sudo chgrp root /boot/grub2/grub.cfg
 The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.
1.3.2 Verify /boot/grub2/grub.cfg Permissions File permissions for /boot/grub2/grub.cfg should be set to 600. To properly set the permissions of /boot/grub2/grub.cfg, run the command: 
$ sudo chmod 600 /boot/grub2/grub.cfg
 Proper permissions ensure that only the root user can modify important boot parameters.
1.3.2 Verify the UEFI Boot Loader grub.cfg Permissions File permissions for /boot/efi/EFI/redhat/grub.cfg should be set to 700. To properly set the permissions of /boot/efi/EFI/redhat/grub.cfg, run the command: 
$ sudo chmod 700 /boot/efi/EFI/redhat/grub.cfg
 Proper permissions ensure that only the root user can modify important boot parameters.
1.3.2 Verify the UEFI Boot Loader grub.cfg User Ownership The file /boot/efi/EFI/redhat/grub.cfg should be owned by the root user to prevent destruction or modification of the file. To properly set the owner of /boot/efi/EFI/redhat/grub.cfg, run the command: 
$ sudo chown root /boot/efi/EFI/redhat/grub.cfg
Only root should be able to modify important boot parameters.
1.3.2 Verify /boot/efi/EFI/redhat/user.cfg Permissions File permissions for /boot/efi/EFI/redhat/user.cfg should be set to 600. To properly set the permissions of /boot/efi/EFI/redhat/user.cfg, run the command: 
$ sudo chmod 600 /boot/efi/EFI/redhat/user.cfg
 Proper permissions ensure that only the root user can read or modify important boot parameters.
1.3.2 Verify /boot/efi/EFI/redhat/user.cfg User Ownership The file /boot/efi/EFI/redhat/user.cfg should be owned by the root user to prevent reading or modification of the file. To properly set the owner of /boot/efi/EFI/redhat/user.cfg, run the command: 
$ sudo chown root /boot/efi/EFI/redhat/user.cfg
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them.
1.3.2 Verify /boot/efi/EFI/redhat/user.cfg Group Ownership The file /boot/efi/EFI/redhat/user.cfg should be group-owned by the root group to prevent reading or modification of the file. To properly set the group owner of /boot/efi/EFI/redhat/user.cfg, run the command: 
$ sudo chgrp root /boot/efi/EFI/redhat/user.cfg
 The root group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway. Non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them.
1.3.2 Verify /boot/grub2/user.cfg User Ownership The file /boot/grub2/user.cfg should be owned by the root user to prevent reading or modification of the file. To properly set the owner of /boot/grub2/user.cfg, run the command: 
$ sudo chown root /boot/grub2/user.cfg
Only root should be able to modify important boot parameters. Also, non-root users who read the boot parameters may be able to identify weaknesses in security upon boot and be able to exploit them.
1.4.1 Enable Randomized Layout of Virtual Address Space To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command: 
$ sudo sysctl -w kernel.randomize_va_space=2
To 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.
1.4.2 Restrict usage of ptrace to descendant processes To set the runtime status of the kernel.yama.ptrace_scope kernel parameter, run the following command: 
$ sudo sysctl -w kernel.yama.ptrace_scope=1
To 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).
1.4.3 Disable core dump backtraces The ProcessSizeMax option in [Coredump] section of /etc/systemd/coredump.conf specifies the maximum size in bytes of a core which will be processed. Core dumps exceeding this size may be stored, but the backtrace will not be generated. 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 or system operators trying to debug problems. Enabling core dumps on production systems is not recommended, however there may be overriding operational requirements to enable advanced debuging. Permitting temporary enablement of core dumps during such situations should be reviewed through local needs and policy.
1.4.4 Disable storing core dump The Storage option in [Coredump] sectionof /etc/systemd/coredump.conf can be set to none to disable storing core dumps permanently. 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 or system operators trying to debug problems. Enabling core dumps on production systems is not recommended, however there may be overriding operational requirements to enable advanced debuging. Permitting temporary enablement of core dumps during such situations should be reviewed through local needs and policy.
1.5.1.1 Install libselinux Package The libselinux package can be installed with the following command: 
$ sudo yum install libselinux
 Security-enhanced Linux is a feature of the Linux kernel and a number of utilities with enhanced security functionality designed to add mandatory access controls to Linux. The libselinux package contains the core library of the Security-enhanced Linux system.
1.5.1.2 Ensure SELinux Not Disabled in /etc/default/grub SELinux can be disabled at boot time by an argument in /etc/default/grub. 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.
1.5.1.3 Configure SELinux Policy The SELinux targeted policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in /etc/selinux/config: 
SELINUXTYPE=targeted
Other policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases. 		Setting the SELinux policy to targeted or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services.

Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to .
1.5.1.4 Ensure SELinux is Not Disabled The SELinux state should be set to enforcing or permissive at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing or permissive mode: 
SELINUX=enforcing
OR 
SELINUX=permissive
 Running SELinux in disabled mode is strongly discouraged. It prevents enforcing the SELinux controls without a system reboot. It also avoids labeling any persistent objects such as files, making it difficult to enable SELinux in the future.
1.5.1.5 Ensure SELinux State is Enforcing The SELinux state should be set to enforcing at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing mode: 
SELINUX=enforcing
 Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.
1.5.1.6 Ensure No Daemons are Unconfined by SELinux Daemons for which the SELinux policy does not contain rules will inherit the context of the parent process. Because daemons are launched during startup and descend from the init process, they inherit the unconfined_service_t context.

To check for unconfined daemons, run the following command: 
$ sudo ps -eZ | grep "unconfined_service_t"
It should produce no output in a well-configured system. 		Daemons which run with the unconfined_service_t context may cause AVC denials, or allow privileges that the daemon does not require.
1.5.1.7 Uninstall mcstrans Package The mcstransd daemon provides category label information to client processes requesting information. The label translations are defined in /etc/selinux/targeted/setrans.conf. The mcstrans package can be removed with the following command: 
$ sudo yum erase mcstrans
 Since this service is not used very often, disable it to reduce the amount of potentially vulnerable code running on the system.
1.5.1.8 Uninstall setroubleshoot Package The SETroubleshoot service notifies desktop users of SELinux denials. The service provides information around configuration errors, unauthorized intrusions, and other potential errors. The setroubleshoot package can be removed with the following command: 
$ sudo yum erase setroubleshoot
 The SETroubleshoot service is an unnecessary daemon to have running on a server, especially if X Windows is removed or disabled.
1.6.1 Configure System Cryptography Policy To configure the system cryptography policy to use ciphers only from the DEFAULT policy, run the following command: 
$ sudo update-crypto-policies --set DEFAULT
The rule checks if settings for selected crypto policy are configured as expected. Configuration files in the /etc/crypto-policies/back-ends are either symlinks to correct files provided by Crypto-policies package or they are regular files in case crypto policy customizations are applied. Crypto policies may be customized by crypto policy modules, in which case it is delimited from the base policy using a colon. 		Centralized cryptographic policies simplify applying secure ciphers across an operating system and the applications that run on that operating system. Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data.
1.7.1 Ensure Message Of The Day Is Configured Properly To configure the system message of the day banner edit the /etc/motd file. Replace the default text with a message compliant with the local site policy. The message should not contain information about operating system version, release, kernel version or patch level. The recommended banner text can be tailored in the XCCDF Value xccdf_org.ssgproject.content_value_cis_banner_text: 
Authorized users only. All activity may be monitored and reported.
Warning messages inform users who are attempting to login to the system of their legal status regarding the system and must include the name of the organization that owns the system and any monitoring policies that are in place. Displaying OS and patch level information in login banners also has the side effect of providing detailed system information to attackers attempting to target specific exploits of a system. Authorized users can easily get this information by running the uname -a command once they have logged in.
1.7.2 Ensure Local Login Warning Banner Is Configured Properly To configure the system local login warning banner edit the /etc/issue file. The contents of this file is displayed to users prior to login to local terminals. Replace the default text with a message compliant with the local site policy. The message should not contain information about operating system version, release, kernel version or patch level. The recommended banner text can be tailored in the XCCDF Value xccdf_org.ssgproject.content_value_cis_banner_text: 
Authorized users only. All activity may be monitored and reported.
Warning messages inform users who are attempting to login to the system of their legal status regarding the system and must include the name of the organization that owns the system and any monitoring policies that are in place. Displaying OS and patch level information in login banners also has the side effect of providing detailed system information to attackers attempting to target specific exploits of a system. Authorized users can easily get this information by running the uname -a command once they have logged in.
1.7.3 Ensure Remote Login Warning Banner Is Configured Properly To configure the system remote login warning banner edit the /etc/issue.net file. The contents of this file is displayed to users prior to login from remote connections. Replace the default text with a message compliant with the local site policy. The message should not contain information about operating system version, release, kernel version or patch level. The recommended banner text can be tailored in the XCCDF Value xccdf_org.ssgproject.content_value_cis_banner_text: 
Authorized users only. All activity may be monitored and reported.
Warning messages inform users who are attempting to login to the system of their legal status regarding the system and must include the name of the organization that owns the system and any monitoring policies that are in place. Displaying OS and patch level information in login banners also has the side effect of providing detailed system information to attackers attempting to target specific exploits of a system. Authorized users can easily get this information by running the uname -a command once they have logged in.
1.7.4 Verify permissions on Message of the Day Banner To properly set the permissions of /etc/motd, run the command: 
$ sudo chmod 0644 /etc/motd
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper permissions will ensure that only root user can modify the banner.
1.7.4 Verify ownership of Message of the Day Banner To properly set the owner of /etc/motd, run the command: 
$ sudo chown root /etc/motd
Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper ownership will ensure that only root user can modify the banner.
1.7.4 Verify Group Ownership of Message of the Day Banner To properly set the group owner of /etc/motd, run the command: 
$ sudo chgrp root /etc/motd
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper group ownership will ensure that only root user can modify the banner.
1.7.5 Verify ownership of System Login Banner To properly set the owner of /etc/issue, run the command: 
$ sudo chown root /etc/issue
Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper ownership will ensure that only root user can modify the banner.
1.7.5 Verify Group Ownership of System Login Banner To properly set the group owner of /etc/issue, run the command: 
$ sudo chgrp root /etc/issue
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper group ownership will ensure that only root user can modify the banner.
1.7.5 Verify permissions on System Login Banner To properly set the permissions of /etc/issue, run the command: 
$ sudo chmod 0644 /etc/issue
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper permissions will ensure that only root user can modify the banner.
1.7.6 Verify Group Ownership of System Login Banner for Remote Connections To properly set the group owner of /etc/issue.net, run the command: 
$ sudo chgrp root /etc/issue.net
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper group ownership will ensure that only root user can modify the banner.
1.7.6 Verify ownership of System Login Banner for Remote Connections To properly set the owner of /etc/issue.net, run the command: 
$ sudo chown root /etc/issue.net
Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper ownership will ensure that only root user can modify the banner.
1.7.6 Verify permissions on System Login Banner for Remote Connections To properly set the permissions of /etc/issue.net, run the command: 
$ sudo chmod 0644 /etc/issue.net
 Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.
Proper permissions will ensure that only root user can modify the banner.
1.8.1 Remove the GDM Package Group By removing the gdm package, the system no longer has GNOME installed installed. If X Windows is not installed then the system cannot boot into graphical user mode. This prevents the system from being accidentally or maliciously booted into a graphical.target mode. To do so, run the following command: 
$ sudo yum remove gdm
 Unnecessary service packages must not be installed to decrease the attack surface of the system. A graphical environment is unnecessary for certain types of systems including a virtualization hypervisor.
1.8.2 Enable GNOME3 Login Warning Banner In the default graphical environment, displaying a login warning banner in the GNOME Display Manager's login screen can be enabled on the login screen by setting banner-message-enable to true.

To enable, add or edit banner-message-enable to /etc/dconf/db/gdm.d/00-security-settings. For example: 
[org/gnome/login-screen]
banner-message-enable=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/login-screen/banner-message-enable
After the settings have been set, run dconf update. The banner text must also be set. 		Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

For U.S. Government systems, system use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.
1.8.2 Set the GNOME3 Login Warning Banner Text In the default graphical environment, configuring the login warning banner text in the GNOME Display Manager's login screen can be configured on the login screen by setting banner-message-text to 'APPROVED_BANNER' where APPROVED_BANNER is the approved banner for your environment.

To enable, add or edit banner-message-text to /etc/dconf/db/gdm.d/00-security-settings. For example: 
[org/gnome/login-screen]
banner-message-text='APPROVED_BANNER'
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/login-screen/banner-message-text
After the settings have been set, run dconf update. When entering a warning banner that spans several lines, remember to begin and end the string with ' and use \n for new lines. 		An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers.
1.8.3 Disable the GNOME3 Login User List In the default graphical environment, users logging directly into the system are greeted with a login screen that displays all known users. This functionality should be disabled by setting disable-user-list to true.

To disable, add or edit disable-user-list to /etc/dconf/db/gdm.d/00-security-settings. For example: 
[org/gnome/login-screen]
disable-user-list=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/login-screen/disable-user-list
After the settings have been set, run dconf update. 		Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to quickly enumerate known user accounts without logging in.
1.8.4 Set GNOME3 Screensaver Inactivity Timeout The idle time-out value for inactivity in the GNOME3 desktop is configured via the idle-delay setting must be set under an appropriate configuration file(s) in the /etc/dconf/db/local.d directory and locked in /etc/dconf/db/local.d/locks directory to prevent user modification.

For example, to configure the system for a 15 minute delay, add the following to /etc/dconf/db/local.d/00-security-settings: 
[org/gnome/desktop/session]
idle-delay=uint32 900
 A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME3 can be configured to identify when a user's session has idled and take action to initiate a session lock.
1.8.4 Set GNOME3 Screensaver Lock Delay After Activation Period To activate the locking delay of the screensaver in the GNOME3 desktop when the screensaver is activated, add or set lock-delay to uint32 0 in /etc/dconf/db/local.d/00-security-settings. For example: 
[org/gnome/desktop/screensaver]
lock-delay=uint32 0
After the settings have been set, run dconf update. 		A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not want to logout because of the temporary nature of the absense.
1.8.5 Ensure Users Cannot Change GNOME3 Screensaver Settings If not already configured, ensure that users cannot change GNOME3 screensaver lock settings by adding /org/gnome/desktop/screensaver/lock-delay to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/desktop/screensaver/lock-delay
After the settings have been set, run dconf update. 		A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock. As such, users should not be allowed to change session settings.
1.8.5 Ensure Users Cannot Change GNOME3 Session Idle Settings If not already configured, ensure that users cannot change GNOME3 session idle settings by adding /org/gnome/desktop/session/idle-delay to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/desktop/session/idle-delay
After the settings have been set, run dconf update. 		A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock. As such, users should not be allowed to change session settings.
1.8.6 Disable GNOME3 Automounting The system's default desktop environment, GNOME3, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. To disable automount within GNOME3, add or set automount to false in /etc/dconf/db/local.d/00-security-settings. For example: 
[org/gnome/desktop/media-handling]
automount=false
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/desktop/media-handling/automount
After the settings have been set, run dconf update. 		Disabling automatic mounting in GNOME3 can prevent the introduction of malware via removable media. It will, however, also prevent desktop users from legitimate use of removable media.
1.8.6 Disable GNOME3 Automount Opening The system's default desktop environment, GNOME3, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. To disable automount-open within GNOME3, add or set automount-open to false in /etc/dconf/db/local.d/00-security-settings. For example: 
[org/gnome/desktop/media-handling]
automount-open=false
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/desktop/media-handling/automount-open
After the settings have been set, run dconf update. 		Automatically mounting file systems permits easy introduction of unknown devices, thereby facilitating malicious activity. Disabling automatic mounting in GNOME3 can prevent the introduction of malware via removable media. It will, however, also prevent desktop users from legitimate use of removable media.
1.8.8 Disable GNOME3 Automount running The system's default desktop environment, GNOME3, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. To disable autorun-never within GNOME3, add or set autorun-never to true in /etc/dconf/db/local.d/00-security-settings. For example: 
[org/gnome/desktop/media-handling]
autorun-never=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example: 
/org/gnome/desktop/media-handling/autorun-never
After the settings have been set, run dconf update. 		Automatically mounting file systems permits easy introduction of unknown devices, thereby facilitating malicious activity. Disabling automatic mount running in GNOME3 can prevent the introduction of malware via removable media. It will, however, also prevent desktop users from legitimate use of removable media.
1.8.10 Disable XDMCP in GDM XDMCP is an unencrypted protocol, and therefore, presents a security risk, see e.g. XDMCP Gnome docs. To disable XDMCP support in Gnome, set Enable to false under the [xdmcp] configuration section in /etc/gdm/custom.conf. For example: 
[xdmcp]
Enable=false
XDMCP provides unencrypted remote access through the Gnome Display Manager (GDM) which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using XDMCP, the privileged user password could be compromised due to typed XEvents and keystrokes will traversing over the network in clear text.
2.1.1 The Chrony package is installed System time should be synchronized between all systems in an environment. This is typically done by establishing an authoritative time server or set of servers and having all systems synchronize their clocks to them. The chrony package can be installed with the following command: 
$ sudo yum install chrony
 Time synchronization is important to support time sensitive security mechanisms like Kerberos and also ensures log files have consistent time records across the enterprise, which aids in forensic investigations.
2.1.2 A remote time server for Chrony is configured Chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on chrony can be found at https://chrony-project.org/. Chrony can be configured to be a client and/or a server. Add or edit server or pool lines to /etc/chrony.conf as appropriate: 
server <remote-server>
Multiple servers may be configured. 		If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly.
2.1.3 Ensure that chronyd is running under chrony user account chrony is a daemon which implements the Network Time Protocol (NTP). It is designed to synchronize system clocks across a variety of systems and use a source that is highly accurate. More information on chrony can be found at https://chrony-project.org/. Chrony can be configured to be a client and/or a server. To ensure that chronyd is running under chrony user account, remove any -u ... option from OPTIONS other than -u chrony, as chrony is run under its own user by default. This recommendation only applies if chrony is in use on the system. If chrony is in use on the system proper configuration is vital to ensuring time synchronization is working properly.
2.2.1 Disable the Automounter The autofs daemon mounts and unmounts filesystems, such as user home directories shared via NFS, on demand. In addition, autofs can be used to handle removable media, and the default configuration provides the cdrom device as /misc/cd. However, this method of providing access to removable media is not common, so autofs can almost always be disabled if NFS is not in use. Even if NFS is required, it may be possible to configure filesystem mounts statically by editing /etc/fstab rather than relying on the automounter.

The autofs service can be disabled with the following command: 
$ sudo systemctl mask --now autofs.service
 Disabling the automounter permits the administrator to statically control filesystem mounting through /etc/fstab.

Additionally, automatically mounting filesystems permits easy introduction of unknown devices, thereby facilitating malicious activity.
2.2.2 Disable Avahi Server Software The avahi-daemon service can be disabled with the following command: 
$ sudo systemctl mask --now avahi-daemon.service
 Because the Avahi daemon service keeps an open network port, it is subject to network attacks. Its functionality is convenient but is only appropriate if the local network can be trusted.
2.2.3 Uninstall DHCP Server Package If the system does not need to act as a DHCP server, the dhcp package can be uninstalled. The dhcp-server package can be removed with the following command: 
$ sudo yum erase dhcp-server
 Removing the DHCP server ensures that it cannot be easily or accidentally reactivated and disrupt network operation.
2.2.4 Uninstall bind Package The named service is provided by the bind package. The bind package can be removed with the following command: 
$ sudo yum erase bind
 If there is no need to make DNS server software available, removing it provides a safeguard against its activation.
2.2.5 Uninstall dnsmasq Package dnsmasq is a lightweight tool that provides DNS caching, DNS forwarding and DHCP (Dynamic Host Configuration Protocol) services.
The dnsmasq package can be removed with the following command: 
$ sudo yum erase dnsmasq
 Unless a system is specifically designated to act as a DNS caching, DNS forwarding and/or DHCP server, it is recommended that the package be removed to reduce the potential attack surface.
2.2.6 Uninstall Samba Package The samba package can be removed with the following command: 
 $ sudo yum erase samba
 If there is no need to make the Samba software available, removing it provides a safeguard against its activation.
2.2.7 Uninstall vsftpd Package The vsftpd package can be removed with the following command: 
 $ sudo yum erase vsftpd
 Removing the vsftpd package decreases the risk of its accidental activation.
2.2.8 Uninstall cyrus-imapd Package The cyrus-imapd package can be removed with the following command: 
$ sudo yum erase cyrus-imapd
 If there is no need to make the cyrus-imapd software available, removing it provides a safeguard against its activation.
2.2.8 Uninstall dovecot Package The dovecot package can be removed with the following command: 
$ sudo yum erase dovecot
 If there is no need to make the Dovecot software available, removing it provides a safeguard against its activation.
2.2.9 Disable Network File System (nfs) The Network File System (NFS) service allows remote hosts to mount and interact with shared filesystems on the local system. If the local system is not designated as a NFS server then this service should be disabled. The nfs-server service can be disabled with the following command: 
$ sudo systemctl mask --now nfs-server.service
 Unnecessary services should be disabled to decrease the attack surface of the system.
2.2.10 Uninstall ypserv Package The ypserv package can be removed with the following command: 
$ sudo yum erase ypserv
 The NIS service provides an unencrypted authentication service which does not provide for the confidentiality and integrity of user passwords or the remote session. Removing the ypserv package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services.
2.2.11 Disable the CUPS Service The cups service can be disabled with the following command: 
$ sudo systemctl mask --now cups.service
 Turn off unneeded services to reduce attack surface.
2.2.12 Disable rpcbind Service The rpcbind utility maps RPC services to the ports on which they listen. RPC processes notify rpcbind when they start, registering the ports they are listening on and the RPC program numbers they expect to serve. The rpcbind service redirects the client to the proper port number so it can communicate with the requested service. If the system does not require RPC (such as for NFS servers) then this service should be disabled. The rpcbind service can be disabled with the following command: 
$ sudo systemctl mask --now rpcbind.service
 If the system does not require rpc based services, it is recommended that rpcbind be disabled to reduce the attack surface.
2.2.13 Uninstall rsync Package The rsyncd service can be used to synchronize files between systems over network links. The rsync-daemon package can be removed with the following command: 
$ sudo yum erase rsync-daemon
 The rsyncd service presents a security risk as it uses unencrypted protocols for communication.
2.2.14 Uninstall net-snmp Package The net-snmp package provides the snmpd service. The net-snmp package can be removed with the following command: 
$ sudo yum erase net-snmp
 If there is no need to run SNMP server software, removing the package provides a safeguard against its activation.
2.2.15 Uninstall telnet-server Package The telnet-server package can be removed with the following command: 
$ sudo yum erase telnet-server
 It is detrimental for operating systems to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities are often overlooked and therefore may remain unsecure. They increase the risk to the platform by providing additional attack vectors.
The telnet service provides an unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using this service, the privileged user password could be compromised.
Removing the telnet-server package decreases the risk of the telnet service's accidental (or intentional) activation.
2.2.16 Uninstall tftp-server Package The tftp-server package can be removed with the following command: 
 $ sudo yum erase tftp-server
 Removing the tftp-server package decreases the risk of the accidental (or intentional) activation of tftp services.

If TFTP is required for operational support (such as transmission of router configurations), its use must be documented with the Information Systems Securty Manager (ISSM), restricted to only authorized personnel, and have access control rules established.
2.2.17 Uninstall squid Package The squid package can be removed with the following command: 
 $ sudo yum erase squid
 If there is no need to make the proxy server software available, removing it provides a safeguard against its activation.
2.2.18 Uninstall nginx Package The nginx package can be removed with the following command: 
$ sudo yum erase nginx
 If there is no need to make the web server software available, removing it provides a safeguard against its activation.
2.2.18 Uninstall httpd Package The httpd package can be removed with the following command: 
$ sudo yum erase httpd
 If there is no need to make the web server software available, removing it provides a safeguard against its activation.
2.2.19 Uninstall xinetd Package The xinetd package can be removed with the following command: 
$ sudo yum erase xinetd
 Removing the xinetd package decreases the risk of the xinetd service's accidental (or intentional) activation.
2.2.20 Remove the X Windows Package Group By removing the xorg-x11-server-common package, the system no longer has X Windows installed. If X Windows is not installed then the system cannot boot into graphical user mode. This prevents the system from being accidentally or maliciously booted into a graphical.target mode. To do so, run the following command:
$ sudo yum groupremove base-x
$ sudo yum remove xorg-x11-server-common
 Unnecessary service packages must not be installed to decrease the attack surface of the system. X windows has a long history of security vulnerabilities and should not be installed unless approved and documented.
2.2.20 Disable X Windows Startup By Setting Default Target Systems that do not require a graphical user interface should only boot by default into multi-user.target mode. This prevents accidental booting of the system into a graphical.target mode. Setting the system's default target to multi-user.target will prevent automatic startup of the X server. To do so, run: 
$ systemctl set-default multi-user.target
You should see the following output: 
Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target.
 Services that are not required for system and application processes must not be active to decrease the attack surface of the system. X windows has a long history of security vulnerabilities and should not be used unless approved and documented.
2.2.21 Ensure Mail Transfer Agent is not Listening on any non-loopback Address Mail Transfer Agents (MTA), such as sendmail and Postfix, are used to listen for incoming mail and transfer the messages to the appropriate user or mail server. If the system is not intended to be a mail server, it is recommended that the MTA be configured to only process local mail. The software for all Mail Transfer Agents is complex and most have a long history of security issues. While it is important to ensure that the system can process local mail messages, it is not necessary to have the MTA's daemon listening on a port unless the server is intended to be a mail server that receives and processes mail from other systems.
2.2.21 Disable Postfix Network Listening Edit the file /etc/postfix/main.cf to ensure that only the following inet_interfaces line appears: 
inet_interfaces = loopback-only
 This ensures postfix accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack.
2.3.1 Remove ftp Package FTP (File Transfer Protocol) is a traditional and widely used standard tool for transferring files between a server and clients over a network, especially where no authentication is necessary (permits anonymous users to connect to a server).
The ftp package can be removed with the following command: 
$ sudo yum erase ftp
 FTP does not protect the confidentiality of data or authentication credentials. It is recommended SFTP be used if file transfer is required. Unless there is a need to run the system as a FTP server (for example, to allow anonymous downloads), it is recommended that the package be removed to reduce the potential attack surface.
2.3.2 Ensure LDAP client is not installed The Lightweight Directory Access Protocol (LDAP) is a service that provides a method for looking up information from a central database. The openldap-clients package can be removed with the following command: 
$ sudo yum erase openldap-clients
 If the system does not need to act as an LDAP client, it is recommended that the software is removed to reduce the potential attack surface.
2.3.3 Remove NIS Client The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server directory service protocol used to distribute system configuration files. The NIS client (ypbind) was used to bind a system to an NIS server and receive the distributed configuration files. The NIS service is inherently an insecure system that has been vulnerable to DOS attacks, buffer overflows and has poor authentication for querying NIS maps. NIS generally has been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is recommended that the service be removed.
2.3.4 Remove telnet Clients The telnet client allows users to start connections to other systems via the telnet protocol. The telnet protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The ssh package provides an encrypted session and stronger security and is included in Red Hat Enterprise Linux 8.
2.3.5 Remove tftp Daemon Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol, typically used to automatically transfer configuration or boot files between systems. TFTP does not support authentication and can be easily hacked. The package tftp is a client program that allows for connections to a tftp server. It is recommended that TFTP be removed, unless there is a specific need for TFTP (such as a boot server). In that case, use extreme caution when configuring the services.
3.1.2 Deactivate Wireless Network Interfaces Deactivating wireless network interfaces should prevent normal usage of the wireless capability.

Configure the system to disable all wireless network interfaces with the following command: 
$ sudo nmcli radio all off
 The use of wireless networking can introduce many different attack vectors into the organization's network. Common attack vectors such as malicious association and ad hoc networks will allow an attacker to spoof a wireless access point (AP), allowing validated systems to connect to the malicious AP and enabling the attacker to monitor and record network traffic. These malicious APs can also serve to create a man-in-the-middle attack or be used to create a denial of service to valid network resources.
3.1.3 Disable Bluetooth Service The bluetooth service can be disabled with the following command: 
$ sudo systemctl mask --now bluetooth.service
$ sudo service bluetooth stop
 Disabling the bluetooth service prevents the system from attempting connections to Bluetooth devices, which entails some security risk. Nevertheless, variation in this risk decision may be expected due to the utility of Bluetooth connectivity and its limited range.
3.2.1 Disable DCCP Support 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
To configure the system to prevent the dccp from being used, add the following line to file /etc/modprobe.d/dccp.conf: 
blacklist dccp
 Disabling DCCP protects the system against exploitation of any flaws in its implementation.
3.2.2 Disable TIPC Support 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
To configure the system to prevent the tipc from being used, add the following line to file /etc/modprobe.d/tipc.conf: 
blacklist tipc
 Disabling TIPC protects the system against exploitation of any flaws in its implementation.
3.2.3 Disable RDS Support 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
To configure the system to prevent the rds from being used, add the following line to file /etc/modprobe.d/rds.conf: 
blacklist rds
 Disabling RDS protects the system against exploitation of any flaws in its implementation.
3.2.4 Disable SCTP Support 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
To configure the system to prevent the sctp from being used, add the following line to file /etc/modprobe.d/sctp.conf: 
blacklist sctp
 Disabling SCTP protects the system against exploitation of any flaws in its implementation.
3.3.1 Disable Kernel Parameter for IP Forwarding on IPv4 Interfaces To set the runtime status of the net.ipv4.ip_forward kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.ip_forward=0
To 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.
3.3.1 Disable Kernel Parameter for IPv6 Forwarding 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=0
To 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.
3.3.2 Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.send_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.send_redirects=0
To 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.
3.3.2 Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.send_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.send_redirects=0
To 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.
3.3.3 Enable Kernel Parameter to Ignore Bogus ICMP Error Responses on IPv4 Interfaces To set the runtime status of the net.ipv4.icmp_ignore_bogus_error_responses kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1
To 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.
3.3.4 Enable Kernel Parameter to Ignore ICMP Broadcast Echo Requests on IPv4 Interfaces 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=1
To 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.
3.3.5 Disable Accepting ICMP Redirects for All IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0
To 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."
3.3.5 Disable Accepting ICMP Redirects for All IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_redirects=0
To 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.
3.3.5 Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv4 Interfaces To set the runtime status of the net.ipv4.conf.default.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0
To 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.
3.3.5 Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv6 Interfaces To set the runtime status of the net.ipv6.conf.default.accept_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_redirects=0
To 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.
3.3.6 Disable Kernel Parameter for Accepting Secure ICMP Redirects on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.secure_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0
To 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.
3.3.6 Configure Kernel Parameter for Accepting Secure Redirects By Default To set the runtime status of the net.ipv4.conf.default.secure_redirects kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.secure_redirects=0
To 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.
3.3.7 Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.rp_filter kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.rp_filter=1
To 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.
3.3.7 Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.rp_filter kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.rp_filter=1
To 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.
3.3.8 Disable Kernel Parameter for Accepting Source-Routed Packets on IPv6 Interfaces by Default To set the runtime status of the net.ipv6.conf.default.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.default.accept_source_route=0
To 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.
3.3.8 Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv6 Interfaces To set the runtime status of the net.ipv6.conf.all.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0
To 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.
3.3.8 Disable Kernel Parameter for Accepting Source-Routed Packets on IPv4 Interfaces by Default To set the runtime status of the net.ipv4.conf.default.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0
To 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.
3.3.8 Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv4 Interfaces To set the runtime status of the net.ipv4.conf.all.accept_source_route kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0
To 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.
3.3.9 Enable Kernel Paremeter to Log Martian Packets on all IPv4 Interfaces by Default 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=1
To 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.
3.3.9 Enable Kernel Parameter to Log Martian Packets on all IPv4 Interfaces 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=1
To 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.
3.3.10 Enable Kernel Parameter to Use TCP Syncookies on Network Interfaces To set the runtime status of the net.ipv4.tcp_syncookies kernel parameter, run the following command: 
$ sudo sysctl -w net.ipv4.tcp_syncookies=1
To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d: 
net.ipv4.tcp_syncookies = 1
 A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests.
3.3.11 Configure Accepting Router Advertisements on All IPv6 Interfaces 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=0
To 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.
3.3.11 Disable Accepting Router Advertisements on all IPv6 Interfaces by Default 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=0
To 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.
3.4.1.1 Install nftables Package nftables provides a new in-kernel packet classification framework that is based on a network-specific Virtual Machine (VM) and a new nft userspace command line tool. nftables reuses the existing Netfilter subsystems such as the existing hook infrastructure, the connection tracking system, NAT, userspace queuing and logging subsystem. The nftables package can be installed with the following command: 
$ sudo yum install nftables
 nftables is a subsystem of the Linux kernel that can protect against threats originating from within a corporate network to include malicious mobile code and poorly configured software on a host.
3.4.1.2 Verify nftables Service is Disabled nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames and is the successor to iptables. The nftables service can be disabled with the following command: 
systemctl disable nftables
 Running both firewalld and nftables may lead to conflict. nftables is actually one of the backends for firewalld management tools.
3.4.1.2 Verify firewalld Enabled The firewalld service can be enabled with the following command: 
$ sudo systemctl enable firewalld.service
 Access control methods provide the ability to enhance system security posture by restricting services and known good IP addresses and address ranges. This prevents connections from unknown hosts and protocols.
3.4.1.2 Install firewalld Package The firewalld package can be installed with the following command: 
$ sudo yum install firewalld
 "Firewalld" provides an easy and effective way to block/limit remote access to the system via ports, services, and protocols. Remote access services, such as those providing remote access to network devices and information systems, which lack automated control capabilities, increase risk and make remote user access management difficult at best. Remote access is access to DoD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless. Red Hat Enterprise Linux 8 functionality (e.g., SSH) must be capable of taking enforcement action if the audit reveals unauthorized activity. Automated control of remote access sessions allows organizations to ensure ongoing compliance with remote access policies by enforcing connection rules of remote access applications on a variety of information system components (e.g., servers, workstations, notebook computers, smartphones, and tablets)."
3.4.2.2 Configure Firewalld to Trust Loopback Traffic Assign loopback interface to the firewalld trusted zone in order to explicitly allow the loopback traffic in the system. To configure firewalld to trust loopback traffic, run the following command: 
sudo firewall-cmd --permanent --zone=trusted --add-interface=lo
To ensure firewalld settings are applied in runtime, run the following command: 
firewall-cmd --reload
 Loopback traffic is generated between processes on machine and is typically critical to operation of the system. The loopback interface is the only place that loopback network traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.
3.4.2.2 Configure Firewalld to Restrict Loopback Traffic Configure firewalld to restrict loopback traffic to the lo interface. The loopback traffic must be trusted by assigning the lo interface to the firewalld trusted zone. However, the loopback traffic must be restricted to the loopback interface as an anti-spoofing measure. To configure firewalld to restrict loopback traffic to the lo interface, run the following commands: 
sudo firewall-cmd --permanent --zone=trusted --add-rich-rule='rule family=ipv4 source address="127.0.0.1" destination not address="127.0.0.1" drop'
sudo firewall-cmd --permanent --zone=trusted --add-rich-rule='rule family=ipv6 source address="::1" destination not address="::1" drop'
To ensure firewalld settings are applied in runtime, run the following command: 
firewall-cmd --reload
 Loopback traffic is generated between processes on machine and is typically critical to operation of the system. The loopback interface is the only place that loopback network traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.
4.1.1.1 Enable cron Service The crond service is used to execute commands at preconfigured times. It is required by almost all systems to perform necessary maintenance tasks, such as notifying root of system activity. The crond service can be enabled with the following command: 
$ sudo systemctl enable crond.service
 Due to its usage for maintenance and security-supporting tasks, enabling the cron daemon is essential.
4.1.1.2 Verify Permissions on crontab To properly set the permissions of /etc/crontab, run the command: 
$ sudo chmod 0600 /etc/crontab
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.2 Verify Owner on crontab To properly set the owner of /etc/crontab, run the command: 
$ sudo chown root /etc/crontab
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.2 Verify Group Who Owns Crontab To properly set the group owner of /etc/crontab, run the command: 
$ sudo chgrp root /etc/crontab
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.3 Verify Owner on cron.hourly To properly set the owner of /etc/cron.hourly, run the command: 
$ sudo chown root /etc/cron.hourly
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.3 Verify Group Who Owns cron.hourly To properly set the group owner of /etc/cron.hourly, run the command: 
$ sudo chgrp root /etc/cron.hourly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.3 Verify Permissions on cron.hourly To properly set the permissions of /etc/cron.hourly, run the command: 
$ sudo chmod 0700 /etc/cron.hourly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.4 Verify Permissions on cron.daily To properly set the permissions of /etc/cron.daily, run the command: 
$ sudo chmod 0700 /etc/cron.daily
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.4 Verify Owner on cron.daily To properly set the owner of /etc/cron.daily, run the command: 
$ sudo chown root /etc/cron.daily
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.4 Verify Group Who Owns cron.daily To properly set the group owner of /etc/cron.daily, run the command: 
$ sudo chgrp root /etc/cron.daily
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.5 Verify Permissions on cron.weekly To properly set the permissions of /etc/cron.weekly, run the command: 
$ sudo chmod 0700 /etc/cron.weekly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.5 Verify Owner on cron.weekly To properly set the owner of /etc/cron.weekly, run the command: 
$ sudo chown root /etc/cron.weekly
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.5 Verify Group Who Owns cron.weekly To properly set the group owner of /etc/cron.weekly, run the command: 
$ sudo chgrp root /etc/cron.weekly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.6 Verify Owner on cron.monthly To properly set the owner of /etc/cron.monthly, run the command: 
$ sudo chown root /etc/cron.monthly
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.6 Verify Group Who Owns cron.monthly To properly set the group owner of /etc/cron.monthly, run the command: 
$ sudo chgrp root /etc/cron.monthly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.6 Verify Permissions on cron.monthly To properly set the permissions of /etc/cron.monthly, run the command: 
$ sudo chmod 0700 /etc/cron.monthly
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.7 Verify Permissions on cron.d To properly set the permissions of /etc/cron.d, run the command: 
$ sudo chmod 0700 /etc/cron.d
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should have the correct access rights to prevent unauthorized changes.
4.1.1.7 Verify Owner on cron.d To properly set the owner of /etc/cron.d, run the command: 
$ sudo chown root /etc/cron.d
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct user to prevent unauthorized changes.
4.1.1.7 Verify Group Who Owns cron.d To properly set the group owner of /etc/cron.d, run the command: 
$ sudo chgrp root /etc/cron.d
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.1.1.8 Verify Group Who Owns /etc/cron.allow file If /etc/cron.allow exists, it must be group-owned by root. To properly set the group owner of /etc/cron.allow, run the command: 
$ sudo chgrp root /etc/cron.allow
 If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.1.8 Verify User Who Owns /etc/cron.allow file If /etc/cron.allow exists, it must be owned by root. To properly set the owner of /etc/cron.allow, run the command: 
$ sudo chown root /etc/cron.allow
If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.1.8 Ensure that /etc/cron.allow exists The file /etc/cron.allow should exist and should be used instead of /etc/cron.deny. Access to crontab should be restricted. It is easier to manage an allow list than a deny list. Therefore, /etc/cron.allow needs to be created and used instead of /etc/cron.deny. Regardless of the existence of any of these files, the root administrative user is always allowed to setup a crontab.
4.1.1.8 Ensure that /etc/cron.deny does not exist The file /etc/cron.deny should not exist. Use /etc/cron.allow instead. Access to cron should be restricted. It is easier to manage an allow list than a deny list.
4.1.1.8 Verify Permissions on /etc/cron.allow file If /etc/cron.allow exists, it must have permissions 0600 or more restrictive. To properly set the permissions of /etc/cron.allow, run the command: 
$ sudo chmod 0600 /etc/cron.allow
 If the permissions of the cron.allow file are not set to 0600 or more restrictive, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.2.1 Verify Group Who Owns /etc/at.allow file If /etc/at.allow exists, it must be group-owned by root. To properly set the group owner of /etc/at.allow, run the command: 
$ sudo chgrp root /etc/at.allow
 If the owner of the at.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.2.1 Verify Permissions on /etc/at.allow file If /etc/at.allow exists, it must have permissions 0600 or more restrictive. To properly set the permissions of /etc/at.allow, run the command: 
$ sudo chmod 0600 /etc/at.allow
 If the permissions of the at.allow file are not set to 0600 or more restrictive, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.2.1 Verify User Who Owns /etc/at.allow file If /etc/at.allow exists, it must be owned by root. To properly set the owner of /etc/at.allow, run the command: 
$ sudo chown root /etc/at.allow
If the owner of the at.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.
4.1.2.1 Ensure that /etc/at.deny does not exist The file /etc/at.deny should not exist. Use /etc/at.allow instead. Access to at should be restricted. It is easier to manage an allow list than a deny list.
4.2.1 Verify Group Who Owns SSH Server config file To properly set the group owner of /etc/ssh/sshd_config, run the command: 
$ sudo chgrp root /etc/ssh/sshd_config
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.2.1 Verify Permissions on SSH Server config file To properly set the permissions of /etc/ssh/sshd_config, run the command: 
$ sudo chmod 0600 /etc/ssh/sshd_config
 Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.2.1 Verify Owner on SSH Server config file To properly set the owner of /etc/ssh/sshd_config, run the command: 
$ sudo chown root /etc/ssh/sshd_config
Service configuration files enable or disable features of their respective services that if configured incorrectly can lead to insecure and vulnerable configurations. Therefore, service configuration files should be owned by the correct group to prevent unauthorized changes.
4.2.2 Verify Group Ownership on SSH Server Private *_key Key Files SSH server private keys, files that match the /etc/ssh/*_key glob, must be group-owned by ssh_keys group. If an unauthorized user obtains the private SSH host key file, the host could be impersonated.
4.2.2 Verify Ownership on SSH Server Private *_key Key Files SSH server private keys, files that match the /etc/ssh/*_key glob, must be owned by root user. If an unauthorized user obtains the private SSH host key file, the host could be impersonated.
4.2.2 Verify Permissions on SSH Server Private *_key Key Files SSH server private keys - files that match the /etc/ssh/*_key glob, have to have restricted permissions. If those files are owned by the root user and the root group, they have to have the 0600 permission or stricter. If they are owned by the root user, but by a dedicated group ssh_keys, they can have the 0640 permission or stricter. If an unauthorized user obtains the private SSH host key file, the host could be impersonated.
4.2.3 Verify Permissions on SSH Server Public *.pub Key Files To properly set the permissions of /etc/ssh/*.pub, run the command: 
$ sudo chmod 0644 /etc/ssh/*.pub
 If a public host key file is modified by an unauthorized user, the SSH service may be compromised.
4.2.3 Verify Ownership on SSH Server Public *.pub Key Files SSH server public keys, files that match the /etc/ssh/*.pub glob, must be owned by root user. If a public host key file is modified by an unauthorized user, the SSH service may be compromised.
4.2.3 Verify Group Ownership on SSH Server Public *.pub Key Files SSH server public keys, files that match the /etc/ssh/*.pub glob, must be group-owned by root group. If a public host key file is modified by an unauthorized user, the SSH service may be compromised.
4.2.4 Limit Users' SSH Access By default, the SSH configuration allows any user with an account to access the system. There are several options available to limit which users and group can access the system via SSH. It is recommended that at least one of the following options be leveraged: - AllowUsers variable gives the system administrator the option of allowing specific users to ssh into the system. The list consists of space separated user names. Numeric user IDs are not recognized with this variable. If a system administrator wants to restrict user access further by specifically allowing a user's access only from a particular host, the entry can be specified in the form of user@host. - AllowGroups variable gives the system administrator the option of allowing specific groups of users to ssh into the system. The list consists of space separated group names. Numeric group IDs are not recognized with this variable. - DenyUsers variable gives the system administrator the option of denying specific users to ssh into the system. The list consists of space separated user names. Numeric user IDs are not recognized with this variable. If a system administrator wants to restrict user access further by specifically denying a user's access from a particular host, the entry can be specified in the form of user@host. - DenyGroups variable gives the system administrator the option of denying specific groups of users to ssh into the system. The list consists of space separated group names. Numeric group IDs are not recognized with this variable. Specifying which accounts are allowed SSH access into the system reduces the possibility of unauthorized access to the system.
4.2.5 Enable SSH Warning Banner To enable the warning banner and ensure it is consistent across the system, add or correct the following line in /etc/ssh/sshd_config: 
Banner /etc/issue.net
Another section contains information on how to create an appropriate system-wide warning banner. 		The warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. Alternatively, systems whose ownership should not be obvious should ensure usage of a banner that does not provide easy attribution.
4.2.6 Use Only FIPS 140-2 Validated Ciphers Limit the ciphers to those algorithms which are FIPS-approved. Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode. The following line in /etc/ssh/sshd_config demonstrates use of FIPS-approved ciphers: 
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc
The man page sshd_config(5) contains a list of supported ciphers. The rule is parametrized to use the following ciphers: aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc,rijndael-cbc@lysator.liu.se. 		Unapproved mechanisms that are used for authentication to the cryptographic module are not verified and therefore cannot be relied upon to provide confidentiality or integrity, and system data may be compromised.
Operating systems utilizing encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules.
FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets industry and government requirements. For government systems, this allows Security Levels 1, 2, 3, or 4 for use on Red Hat Enterprise Linux 8.
4.2.7 Set SSH Client Alive Interval SSH allows administrators to set a network responsiveness timeout interval. After this interval has passed, the unresponsive client will be automatically logged out.

To set this timeout interval, edit the following line in /etc/ssh/sshd_config as follows: 
ClientAliveInterval 300


The timeout interval is given in seconds. For example, have a timeout of 10 minutes, set interval to 600.

If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made in /etc/ssh/sshd_config. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle. 		Terminating an idle ssh session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been let unattended.
4.2.7 Set SSH Client Alive Count Max The SSH server sends at most ClientAliveCountMax messages during a SSH session and waits for a response from the SSH client. The option ClientAliveInterval configures timeout after each ClientAliveCountMax message. If the SSH server does not receive a response from the client, then the connection is considered unresponsive and terminated. For SSH earlier than v8.2, a ClientAliveCountMax value of 0 causes a timeout precisely when the ClientAliveInterval is set. Starting with v8.2, a value of 0 disables the timeout functionality completely. If the option is set to a number greater than 0, then the session will be disconnected after ClientAliveInterval * ClientAliveCountMax seconds without receiving a keep alive message. This ensures a user login will be terminated as soon as the ClientAliveInterval is reached.
4.2.9 Disable Host-Based Authentication SSH's cryptographic host-based authentication is more secure than .rhosts authentication. However, it is not recommended that hosts unilaterally trust one another, even within an organization.
The default SSH configuration disables host-based authentication. The appropriate configuration is used if no value is set for HostbasedAuthentication.
To explicitly disable host-based authentication, add or correct the following line in /etc/ssh/sshd_config: 
HostbasedAuthentication no
 SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.
4.2.10 Disable SSH Support for .rhosts Files SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via .rhosts files.
The default SSH configuration disables support for .rhosts. The appropriate configuration is used if no value is set for IgnoreRhosts.
To explicitly disable support for .rhosts files, add or correct the following line in /etc/ssh/sshd_config: 
IgnoreRhosts yes
 SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.
4.2.11 Use Only Strong Key Exchange algorithms Limit the Key Exchange to strong algorithms. The following line in /etc/ssh/sshd_config demonstrates use of those: 
KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256
 Key exchange is any method in cryptography by which cryptographic keys are exchanged between two parties, allowing use of a cryptographic algorithm. If the sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received
4.2.12 Ensure SSH LoginGraceTime is configured The LoginGraceTime parameter to the SSH server specifies the time allowed for successful authentication to the SSH server. The longer the Grace period is the more open unauthenticated connections can exist. Like other session controls in this session the Grace Period should be limited to appropriate limits to ensure the service is available for needed access. Setting the LoginGraceTime parameter to a low number will minimize the risk of successful brute force attacks to the SSH server. It will also limit the number of concurrent unauthenticated connections.
4.2.13 Set SSH Daemon LogLevel to VERBOSE The VERBOSE parameter configures the SSH daemon to record login and logout activity. To specify the log level in SSH, add or correct the following line in /etc/ssh/sshd_config: 
LogLevel VERBOSE
 SSH provides several logging levels with varying amounts of verbosity. DEBUG is specifically not recommended other than strictly for debugging SSH communications since it provides so much data that it is difficult to identify important security information. INFO or VERBOSE level is the basic level that only records login activity of SSH users. In many situations, such as Incident Response, it is important to determine when a particular user was active on a system. The logout record can eliminate those users who disconnected, which helps narrow the field.
4.2.14 Use Only Strong MACs Limit the MACs to strong hash algorithms. The following line in /etc/ssh/sshd_config demonstrates use of those MACs: 
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
 MD5 and 96-bit MAC algorithms are considered weak and have been shown to increase exploitability in SSH downgrade attacks. Weak algorithms continue to have a great deal of attention as a weak spot that can be exploited with expanded computing power. An attacker that breaks the algorithm could take advantage of a MiTM position to decrypt the SSH tunnel and capture credentials and information
4.2.15 Set SSH authentication attempt limit The MaxAuthTries parameter specifies the maximum number of authentication attempts permitted per connection. Once the number of failures reaches half this value, additional failures are logged. to set MaxAUthTries edit /etc/ssh/sshd_config as follows: 
MaxAuthTries 4
 Setting the MaxAuthTries parameter to a low number will minimize the risk of successful brute force attacks to the SSH server.
4.2.16 Set SSH MaxSessions limit The MaxSessions parameter specifies the maximum number of open sessions permitted from a given connection. To set MaxSessions edit /etc/ssh/sshd_config as follows: 
MaxSessions 10
 To protect a system from denial of service due to a large number of concurrent sessions, use the rate limiting function of MaxSessions to protect availability of sshd logins and prevent overwhelming the daemon.
4.2.17 Ensure SSH MaxStartups is configured The MaxStartups parameter specifies the maximum number of concurrent unauthenticated connections to the SSH daemon. Additional connections will be dropped until authentication succeeds or the LoginGraceTime expires for a connection. To configure MaxStartups, you should add or edit the following line in the /etc/ssh/sshd_config file: 
MaxStartups 10:30:100
 To protect a system from denial of service due to a large number of pending authentication connection attempts, use the rate limiting function of MaxStartups to protect availability of sshd logins and prevent overwhelming the daemon.
4.2.18 Disable SSH Access via Empty Passwords Disallow SSH login with empty passwords. The default SSH configuration disables logins with empty passwords. The appropriate configuration is used if no value is set for PermitEmptyPasswords.
To explicitly disallow SSH login from accounts with empty passwords, add or correct the following line in /etc/ssh/sshd_config: 
PermitEmptyPasswords no
Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords. 		Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.
4.2.19 Disable SSH Root Login The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in /etc/ssh/sshd_config: 
PermitRootLogin no
 Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password.
4.2.20 Do Not Allow SSH Environment Options Ensure that users are not able to override environment variables of the SSH daemon.
The default SSH configuration disables environment processing. The appropriate configuration is used if no value is set for PermitUserEnvironment.
To explicitly disable Environment options, add or correct the following /etc/ssh/sshd_config: 
PermitUserEnvironment no
 SSH environment options potentially allow users to bypass access restriction in some configurations.
4.2.21 Enable PAM UsePAM Enables the Pluggable Authentication Module interface. If set to “yes” this will enable PAM authentication using ChallengeResponseAuthentication and PasswordAuthentication in addition to PAM account and session module processing for all authentication types. To enable PAM authentication, add or correct the following line in /etc/ssh/sshd_config: 
UsePAM yes
 When UsePAM is set to yes, PAM runs through account and session types properly. This is important if you want to restrict access to services based off of IP, time or other factors of the account. Additionally, you can make sure users inherit certain environment variables on login or disallow access to the server.
4.2.22 Configure SSH to use System Crypto Policy Crypto Policies provide a centralized control over crypto algorithms usage of many packages. SSH is supported by crypto policy, but the SSH configuration may be set up to ignore it. To check that Crypto Policies settings are configured correctly, ensure that the CRYPTO_POLICY variable is either commented or not set at all in the /etc/sysconfig/sshd. Overriding the system crypto policy makes the behavior of the SSH service violate expectations, and makes system configuration more fragmented.
4.3.1 Install sudo Package The sudo package can be installed with the following command: 
$ sudo yum install sudo
 sudo is a program designed to allow a system administrator to give limited root privileges to users and log root activity. The basic philosophy is to give as few privileges as possible but still allow system users to get their work done.
4.3.2 Ensure Only Users Logged In To Real tty Can Execute Sudo - sudo use_pty The sudo use_pty tag, when specified, will only execute sudo commands from users logged in to a real tty. This should be enabled by making sure that the use_pty tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. Requiring that sudo commands be run in a pseudo-terminal can prevent an attacker from retaining access to the user's terminal after the main program has finished executing.
4.3.3 Ensure Sudo Logfile Exists - sudo logfile A custom log sudo file can be configured with the 'logfile' tag. This rule configures a sudo custom logfile at the default location suggested by CIS, which uses /var/log/sudo.log. A sudo log file simplifies auditing of sudo commands.
4.3.4
4.3.5		 Ensure Users Re-Authenticate for Privilege Escalation - sudo The sudo NOPASSWD and !authenticate option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that NOPASSWD and/or !authenticate do not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/." Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
4.3.6 Require Re-Authentication When Using the sudo Command The sudo timestamp_timeout tag sets the amount of time sudo password prompt waits. The default timestamp_timeout value is 5 minutes. The timestamp_timeout should be configured by making sure that the timestamp_timeout tag exists in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/. If the value is set to an integer less than 0, the user's time stamp will not expire and the user will not have to re-authenticate for privileged actions until the user's session is terminated. Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.
4.3.7 Enforce Usage of pam_wheel with Group Parameter for su Authentication To ensure that only users who are members of the group set in the group option of pam_wheel.so module can run commands with altered privileges through the su command, make sure that the following line exists in the file /etc/pam.d/su: 
auth required pam_wheel.so use_uid group=sugroup
 The su program allows to run commands with a substitute user and group ID. It is commonly used to run commands as the root user. Limiting access to such command is considered a good security practice.
4.3.7 Ensure the Group Used by pam_wheel.so Module Exists on System and is Empty Ensure that the group sugroup referenced by var_pam_wheel_group_for_su variable and used as value for the pam_wheel.so group option exists and has no members. This empty group used by pam_wheel.so in /etc/pam.d/su ensures that no user can run commands with altered privileges through the su command. The su program allows to run commands with a substitute user and group ID. It is commonly used to run commands as the root user. Limiting access to such command is considered a good security practice.
4.4.2.2 Configure the Use of the pam_faillock.so Module in the /etc/pam.d/system-auth File. The pam_faillock.so module must be loaded in preauth in /etc/pam.d/system-auth. If the pam_faillock.so module is not loaded the system will not correctly lockout accounts to prevent password guessing attacks.
4.4.2.2 Configure the Use of the pam_faillock.so Module in the /etc/pam.d/password-auth File. The pam_faillock.so module must be loaded in preauth in /etc/pam.d/password-auth. If the pam_faillock.so module is not loaded the system will not correctly lockout accounts to prevent password guessing attacks.
4.4.2.3 Install pam_pwquality Package The libpwquality package can be installed with the following command: 
$ sudo yum install libpwquality
 Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. "pwquality" enforces complex password construction configuration and has the ability to limit brute-force attacks on the system.
4.4.3.1.1 Lock Accounts After Failed Password Attempts This rule configures the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. Ensure that the file /etc/security/faillock.conf contains the following entry: deny = <count> Where count should be less than or equal to 3 and greater than 0. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account.
4.4.3.1.2 Set Lockout Time for Failed Password Attempts This rule configures the system to lock out accounts during a specified time period after a number of incorrect login attempts using pam_faillock.so. Ensure that the file /etc/security/faillock.conf contains the following entry: unlock_time=<interval-in-seconds> where interval-in-seconds is 0 or greater. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid any errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. If unlock_time is set to 0, manual intervention by an administrator is required to unlock a user. This should be done using the faillock tool. By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.
4.4.3.1.3 Configure the root Account for Failed Password Attempts This rule configures the system to lock out the root account after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version. By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, also known as brute-forcing, is reduced. Limits are imposed by locking the account.
4.4.3.2.1 Ensure PAM Enforces Password Requirements - Minimum Different Characters The pam_pwquality module's difok parameter sets the number of characters in a password that must not be present in and old password during a password change.

Modify the difok setting in /etc/security/pwquality.conf to equal 8 to require differing characters when changing passwords. 		Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute–force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Requiring a minimum number of different characters during password changes ensures that newly changed passwords should not resemble previously compromised ones. Note that passwords which are changed on compromised systems will still be compromised, however.
4.4.3.2.2 Ensure PAM Enforces Password Requirements - Minimum Length The pam_pwquality module's minlen parameter controls requirements for minimum characters required in a password. Add minlen=15 after pam_pwquality to set minimum password length requirements. The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromise the password.
4.4.3.2.3 Ensure PAM Enforces Password Requirements - Minimum Different Categories The pam_pwquality module's minclass parameter controls requirements for usage of different character classes, or types, of character that must exist in a password before it is considered valid. For example, setting this value to three (3) requires that any password must have characters from at least three different categories in order to be approved. The default value is zero (0), meaning there are no required classes. There are four categories available: 
* Upper-case characters
* Lower-case characters
* Digits
* Special characters (for example, punctuation)
Modify the minclass setting in /etc/security/pwquality.conf entry to require 3 differing categories of characters when changing passwords. 		Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Requiring a minimum number of character categories makes password guessing attacks more difficult by ensuring a larger search space.
4.4.3.2.4 Set Password Maximum Consecutive Repeating Characters The pam_pwquality module's maxrepeat parameter controls requirements for consecutive repeating characters. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters. Modify the maxrepeat setting in /etc/security/pwquality.conf to equal 3 to prevent a run of (3 + 1) or more identical characters. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Passwords with excessive repeating characters may be more vulnerable to password-guessing attacks.
4.4.3.2.6 Ensure PAM Enforces Password Requirements - Prevent the Use of Dictionary Words The pam_pwquality module's dictcheck check if passwords contains dictionary words. When dictcheck is set to 1 passwords will be checked for dictionary words. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Passwords with dictionary words may be more vulnerable to password-guessing attacks.
4.4.3.2.7 Ensure PAM Enforces Password Requirements - Enforce for root User The pam_pwquality module's enforce_for_root parameter controls requirements for enforcing password complexity for the root user. Enable the enforce_for_root setting in /etc/security/pwquality.conf to require the root user to use complex passwords. Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.
4.4.3.3.1 Limit Password Reuse: password-auth Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_pwhistory PAM module.

On systems with newer versions of authselect, the pam_pwhistory PAM module can be enabled via authselect feature: 
authselect enable-feature with-pwhistory
Otherwise, it should be enabled using an authselect custom profile.

Newer systems also have the /etc/security/pwhistory.conf file for setting pam_pwhistory module options. This file should be used whenever available. Otherwise, the pam_pwhistory module options can be set in PAM files.

The value for remember option must be equal or greater than 5 		Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.
4.4.3.3.1 Limit Password Reuse: system-auth Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_pwhistory PAM module.

On systems with newer versions of authselect, the pam_pwhistory PAM module can be enabled via authselect feature: 
authselect enable-feature with-pwhistory
Otherwise, it should be enabled using an authselect custom profile.

Newer systems also have the /etc/security/pwhistory.conf file for setting pam_pwhistory module options. This file should be used whenever available. Otherwise, the pam_pwhistory module options can be set in PAM files.

The value for remember option must be equal or greater than 5 		Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.
4.4.3.4.1 Prevent Login to Accounts With Empty Password If an account is configured for password authentication but does not have an assigned password, it may be possible to log into the account without authentication. Remove any instances of the nullok in /etc/pam.d/system-auth and /etc/pam.d/password-auth to prevent logins with empty passwords. If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.
4.4.3.4.3 Set PAM''s Password Hashing Algorithm - password-auth The PAM system service can be configured to only store encrypted representations of passwords. In /etc/pam.d/password-auth, the password section of the file controls which PAM modules to execute during a password change. Set the pam_unix.so module in the password section to include the option sha512 and no other hashing algorithms as shown below: 
password    sufficient    pam_unix.so sha512 other arguments...

This will help ensure that new passwords for local users will be stored using the sha512 algorithm. 		Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option in /etc/libuser.conf ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.
4.4.3.4.3 Set PAM''s Password Hashing Algorithm The PAM system service can be configured to only store encrypted representations of passwords. In "/etc/pam.d/system-auth", the password section of the file controls which PAM modules to execute during a password change. Set the pam_unix.so module in the password section to include the option sha512 and no other hashing algorithms as shown below: 
password    sufficient    pam_unix.so sha512 other arguments...

This will help ensure that new passwords for local users will be stored using the sha512 algorithm. 		Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option in /etc/libuser.conf ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.
4.5.1.1 Set Password Hashing Algorithm in /etc/login.defs In /etc/login.defs, add or update the following line to ensure the system will use SHA512 as the hashing algorithm: 
ENCRYPT_METHOD SHA512
 Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

Using a stronger hashing algorithm makes password cracking attacks more difficult.
4.5.1.1 Set Password Hashing Algorithm in /etc/libuser.conf In /etc/libuser.conf, add or correct the following line in its [defaults] section to ensure the system will use the sha512 algorithm for password hashing: 
crypt_style = sha512
 Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option in /etc/libuser.conf ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.
4.5.1.2 Set Existing Passwords Maximum Age Configure non-compliant accounts to enforce a 60-day maximum password lifetime restriction by running the following command: 
$ sudo chage -M 60 USER
 Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If the operating system does not limit the lifetime of passwords and force users to change their passwords, there is the risk that the operating system passwords could be compromised.
4.5.1.2 Set Password Maximum Age To specify password maximum age for new accounts, edit the file /etc/login.defs and add or correct the following line: 
PASS_MAX_DAYS 60
A value of 180 days is sufficient for many environments. The DoD requirement is 60. The profile requirement is 60. 		Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If the operating system does not limit the lifetime of passwords and force users to change their passwords, there is the risk that the operating system passwords could be compromised.

Setting the password maximum age ensures users are required to periodically change their passwords. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise.
4.5.1.3 Set Existing Passwords Warning Age To configure how many days prior to password expiration that a warning will be issued to users, run the command: 
$ sudo chage --warndays 7 USER
The DoD requirement is 7, and CIS recommendation is no less than 7 days. This profile requirement is 7. 		Providing an advance warning that a password will be expiring gives users time to think of a secure password. Users caught unaware may choose a simple password or write it down where it may be discovered.
4.5.1.3 Set Password Warning Age To specify how many days prior to password expiration that a warning will be issued to users, edit the file /etc/login.defs and add or correct the following line: 
PASS_WARN_AGE 7
The DoD requirement is 7. The profile requirement is 7. 		Setting the password warning age enables users to make the change at a practical time.
4.5.1.4 Set existing passwords a period of inactivity before they been locked Configure user accounts that have been inactive for over a given period of time to be automatically disabled by running the following command: 
$ sudo chage --inactive 30USER
 Inactive accounts pose a threat to system security since the users are not logging in to notice failed login attempts or other anomalies.
4.5.1.4 Set Account Expiration Following Inactivity To specify the number of days after a password expires (which signifies inactivity) until an account is permanently disabled, add or correct the following line in /etc/default/useradd: 
INACTIVE=35
If a password is currently on the verge of expiration, then 35 day(s) remain(s) until the account is automatically disabled. However, if the password will not expire for another 60 days, then 60 days plus 35 day(s) could elapse until the account would be automatically disabled. See the useradd man page for more information. 		Inactive identifiers pose a risk to systems and applications because attackers may exploit an inactive identifier and potentially obtain undetected access to the system. Disabling inactive accounts ensures that accounts which may not have been responsibly removed are not available to attackers who may have compromised their credentials. Owners of inactive accounts will not notice if unauthorized access to their user account has been obtained.
4.5.1.5 Ensure all users last password change date is in the past All users should have a password change date in the past. If a user recorded password change date is in the future then they could bypass any set password expiration.
4.5.2.1 Verify Root Has A Primary GID 0 The root user should have a primary group of 0. To help ensure that root-owned files are not inadvertently exposed to other users.
4.5.2.3 Ensure that System Accounts Do Not Run a Shell Upon Login Some accounts are not associated with a human user of the system, and exist to perform some administrative functions. Should an attacker be able to log into these accounts, they should not be granted access to a shell.

The login shell for each local account is stored in the last field of each line in /etc/passwd. System accounts are those user accounts with a user ID less than 1000. The user ID is stored in the third field. If any system account other than root has a login shell, disable it with the command: 
$ sudo usermod -s /sbin/nologin account
 Ensuring shells are not given to system accounts upon login makes it more difficult for attackers to make use of system accounts.
4.5.2.3 Ensure that System Accounts Are Locked Some accounts are not associated with a human user of the system, and exist to perform some administrative functions. An attacker should not be able to log into these accounts.

System accounts are those user accounts with a user ID less than 1000. If any system account other than root, halt, sync, shutdown and nfsnobody has an unlocked password, disable it with the command: 
$ sudo usermod -L account
 Disabling authentication for default system accounts makes it more difficult for attackers to make use of them to compromise a system.
4.5.2.4 Ensure Authentication Required for Single User Mode Single user mode is used for recovery when the system detects an issue during boot or by manual selection from the bootloader. Requiring authentication in single user mode prevents an unauthorized user from rebooting the system into single user to gain root privileges without credentials.
4.5.3.2 Set Interactive Session Timeout Setting the TMOUT option in /etc/profile ensures that all user sessions will terminate based on inactivity. The value of TMOUT should be exported and read only. The TMOUT setting in a file loaded by /etc/profile, e.g. /etc/profile.d/tmout.sh should read as follows: 
typeset -xr TMOUT=600
or 
declare -xr TMOUT=600
Using the typeset keyword is preferred for wider compatibility with ksh and other shells. 		Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended.
4.5.3.3 Ensure the Default Umask is Set Correctly in login.defs To ensure the default umask controlled by /etc/login.defs is set properly, add or correct the UMASK setting in /etc/login.defs to read as follows: 
UMASK 027
 The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and written to by unauthorized users.
4.5.3.3 Ensure the Default Umask is Set Correctly in /etc/profile To ensure the default umask controlled by /etc/profile is set properly, add or correct the umask setting in /etc/profile to read as follows: 
umask 027
Note that /etc/profile also reads scrips within /etc/profile.d directory. These scripts are also valid files to set umask value. Therefore, they should also be considered during the check and properly remediated, if necessary. 		The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users.
4.5.3.3 Ensure the Default Bash Umask is Set Correctly To ensure the default umask for users of the Bash shell is set properly, add or correct the umask setting in /etc/bashrc to read as follows: 
umask 027
 The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read or written to by unauthorized users.
5.1.1.1 Ensure rsyslog is Installed Rsyslog is installed by default. The rsyslog package can be installed with the following command: 
 $ sudo yum install rsyslog
 The rsyslog package provides the rsyslog daemon, which provides system logging services.
5.1.1.2 Enable rsyslog Service The rsyslog service provides syslog-style logging by default on Red Hat Enterprise Linux 8. The rsyslog service can be enabled with the following command: 
$ sudo systemctl enable rsyslog.service
 The rsyslog service must be running in order to provide logging services, which are essential to system administration.
5.1.1.3 Ensure journald is configured to send logs to rsyslog Data from journald may be stored in volatile memory or persisted locally. Utilities exist to accept remote export of journald logs. Storing log data on a remote host protects log integrity from local attacks. If an attacker gains root access on the local system, they could tamper with or remove log data that is stored on the local system.
5.1.1.4 Ensure rsyslog Default File Permissions Configured rsyslog will create logfiles that do not already exist on the system. This settings controls what permissions will be applied to these newly created files. It is important to ensure that log files have the correct permissions to ensure that sensitive data is archived and protected.
5.1.1.7 Ensure rsyslog Does Not Accept Remote Messages Unless Acting As Log Server The rsyslog daemon should not accept remote messages unless the system acts as a log server. To ensure that it is not listening on the network, ensure any of the following lines are not found in rsyslog configuration files. If using legacy syntax: 
$ModLoad imtcp
$InputTCPServerRun port
$ModLoad imudp
$UDPServerRun port
$ModLoad imrelp
$InputRELPServerRun port
If using RainerScript syntax: 
module(load="imtcp")
module(load="imudp")
input(type="imtcp" port="514")
input(type="imudp" port="514")
Any process which receives messages from the network incurs some risk of receiving malicious messages. This risk can be eliminated for rsyslog by configuring it not to listen on the network.
5.1.2.1.4 Disable systemd-journal-remote Socket Journald supports the ability to receive messages from remote hosts, thus acting as a log server. Clients should not receive data from other hosts. NOTE: The same package, systemd-journal-remote , is used for both sending logs to remote hosts and receiving incoming logs. With regards to receiving logs, there are two Systemd unit files; systemd-journal-remote.socket and systemd-journal-remote.service. If a client is configured to also receive data, thus turning it into a server, the client system is acting outside it's operational boundary.
5.1.2.2 Enable systemd-journald Service The systemd-journald service is an essential component of systemd. The systemd-journald service can be enabled with the following command: 
$ sudo systemctl enable systemd-journald.service
 In the event of a system failure, Red Hat Enterprise Linux 8 must preserve any information necessary to determine cause of failure and any information necessary to return to operations with least disruption to system processes.
5.1.2.3 Ensure journald is configured to compress large log files The journald system can compress large log files to avoid fill the system disk. Log files that are not properly compressed run the risk of growing so large that they fill up the log partition. Valuable logging information could be lost if the log partition becomes full.
5.1.2.4 Ensure journald is configured to write log files to persistent disk The journald system may store log files in volatile memory or locally on disk. If the logs are only stored in volatile memory they will we lost upon reboot. Log files contain valuable data and need to be persistent to aid in possible investigations.
5.1.4 Ensure System Log Files Have Correct Permissions The file permissions for all log files written by rsyslog should be set to 640, or more restrictive. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's permissions: 
$ ls -l LOGFILE
If the permissions are not 640 or more restrictive, run the following command to correct this: 
$ sudo chmod 640 LOGFILE
" 		Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value.
5.1.4 Ensure Log Files Are Owned By Appropriate User The owner of all log files written by rsyslog should be root. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's owner: 
$ ls -l LOGFILE
If the owner is not root, run the following command to correct this: 
$ sudo chown root LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
5.1.4 Ensure Log Files Are Owned By Appropriate Group The group-owner of all log files written by rsyslog should be root. These log files are determined by the second part of each Rule line in /etc/rsyslog.conf and typically all appear in /var/log. For each log file LOGFILE referenced in /etc/rsyslog.conf, run the following command to inspect the file's group owner: 
$ ls -l LOGFILE
If the owner is not root, run the following command to correct this: 
$ sudo chgrp root LOGFILE
 The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.
5.2.1.1 Ensure the audit Subsystem is Installed The audit package should be installed. The auditd service is an access monitoring and accounting daemon, watching system calls to audit any access, in comparison with potential local access control policy such as SELinux policy.
5.2.1.2 Enable Auditing for Processes Which Start Prior to the Audit Daemon To ensure all processes can be audited, even those which start prior to the audit daemon, add the argument audit=1 to the default GRUB 2 command line for the Linux operating system. To ensure that audit=1 is added as a kernel command line argument to newly installed kernels, add audit=1 to the default Grub2 command line for Linux operating systems. Modify the line within /etc/default/grub as shown below: 
GRUB_CMDLINE_LINUX="... audit=1 ..."
Run the following command to update command line for already installed kernels:
# grubby --update-kernel=ALL --args="audit=1"
 Each process on the system carries an "auditable" flag which indicates whether its activities can be audited. Although auditd takes care of enabling this for all processes which launch after it does, adding the kernel argument ensures it is set for every process during boot.
5.2.1.3 Extend Audit Backlog Limit for the Audit Daemon 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 the default GRUB 2 command line for the Linux operating system. To ensure that audit_backlog_limit=8192 is added as a kernel command line argument to newly installed kernels, add audit_backlog_limit=8192 to the default Grub2 command line for Linux operating systems. Modify the line within /etc/default/grub as shown below: 
GRUB_CMDLINE_LINUX="... audit_backlog_limit=8192 ..."
Run the following command to update command line for already installed kernels:
# grubby --update-kernel=ALL --args="audit_backlog_limit=8192"
 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.
5.2.1.4 Enable auditd Service The auditd service is an essential userspace component of the Linux Auditing System, as it is responsible for writing audit records to disk. The auditd service can be enabled with the following command: 
$ sudo systemctl enable auditd.service
 Without establishing what type of events occurred, it would be difficult to establish, correlate, and investigate the events leading up to an outage or attack. Ensuring the auditd service is active ensures audit records generated by the kernel are appropriately recorded.

Additionally, a properly configured audit subsystem ensures that actions of individual system users can be uniquely traced to those users so they can be held accountable for their actions.
5.2.2.1 Configure auditd Max Log File Size Determine the amount of audit data (in megabytes) which should be retained in each log file. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting the correct value of 6 for STOREMB: 
max_log_file = STOREMB
Set the value to 6 (MB) or higher for general-purpose systems. Larger values, of course, support retention of even more audit data. 		The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.
5.2.2.2 Configure auditd max_log_file_action Upon Reaching Maximum Log Size The default action to take when the logs reach their maximum size is to rotate the log files, discarding the oldest one. To configure the action taken by auditd, add or correct the line in /etc/audit/auditd.conf: 
max_log_file_action = ACTION
Possible values for ACTION are described in the auditd.conf man page. These include:
  • ignore
  • syslog
  • suspend
  • rotate
  • keep_logs
Set the ACTION to rotate. The setting is case-insensitive. 		Automatically rotating logs (by setting this to rotate) minimizes the chances of the system unexpectedly running out of disk space by being overwhelmed with log data. However, for systems that must never discard log data, or which use external processes to transfer it and reclaim space, keep_logs can be employed.
5.2.2.3 Configure auditd Disk Full Action when Disk Space Is Full The auditd service can be configured to take an action when disk space is running low but prior to running out of space completely. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting ACTION appropriately: 
disk_full_action = ACTION
Set this value to single to cause the system to switch to single-user mode for corrective action. Acceptable values also include syslog, exec, single, and halt. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the auditd.conf man page. 		Taking appropriate action in case of a filled audit storage volume will minimize the possibility of losing audit records.
5.2.2.3 Configure auditd Disk Error Action on Disk Error The auditd service can be configured to take an action when there is a disk error. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting ACTION appropriately: 
disk_error_action = ACTION
Set this value to single to cause the system to switch to single-user mode for corrective action. Acceptable values also include syslog, exec, single, and halt. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the auditd.conf man page. 		Taking appropriate action in case of disk errors will minimize the possibility of losing audit records.
5.2.2.4 Configure auditd mail_acct Action on Low Disk Space The auditd service can be configured to send email to a designated account in certain situations. Add or correct the following line in /etc/audit/auditd.conf to ensure that administrators are notified via email for those situations: 
action_mail_acct = root
 Email sent to the root account is typically aliased to the administrators of the system, who can take appropriate action.
5.2.2.4 Configure auditd admin_space_left Action on Low Disk Space The auditd service can be configured to take an action when disk space is running low but prior to running out of space completely. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting ACTION appropriately: 
admin_space_left_action = ACTION
Set this value to single to cause the system to switch to single user mode for corrective action. Acceptable values also include suspend and halt. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the auditd.conf man page. 		Administrators should be made aware of an inability to record audit records. If a separate partition or logical volume of adequate size is used, running low on space for audit records should never occur.
5.2.2.4 Configure auditd space_left Action on Low Disk Space The auditd service can be configured to take an action when disk space starts to run low. Edit the file /etc/audit/auditd.conf. Modify the following line, substituting ACTION appropriately: 
space_left_action = ACTION
Possible values for ACTION are described in the auditd.conf man page. These include:
  • syslog
  • email
  • exec
  • suspend
  • single
  • halt
Set this to email (instead of the default, which is suspend) as it is more likely to get prompt attention. Acceptable values also include suspend, single, and halt. 		Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption.
5.2.3.1 Ensure auditd Collects System Administrator Actions At a minimum, the audit system should collect administrator actions for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-w /etc/sudoers -p wa -k actions
-w /etc/sudoers.d/ -p wa -k actions
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-w /etc/sudoers -p wa -k actions
-w /etc/sudoers.d/ -p wa -k actions
 The actions taken by system administrators should be audited to keep a record of what was executed on the system, as well as, for accountability purposes.
5.2.3.2 Record Events When Executables Are Run As Another User Verify the system generates an audit record when actions are run as another user. sudo provides users with temporary elevated privileges to perform operations, either as the superuser or another user. If audit is using the "auditctl" tool to load the rules, run the following command: 
$ sudo grep execve /etc/audit/audit.rules
If audit is using the "augenrules" tool to load the rules, run the following command: 
$ sudo grep -r execve /etc/audit/rules.d
-a always,exit -F arch=b32 -S execve -C euid!=uid -F auid!=unset -k user_emulation
-a always,exit -F arch=b64  S execve -C euid!=uid -F auid!=unset -k user_emulation
If both the "b32" and "b64" audit rules for "SUID" files are not defined, this is a finding. 		Creating an audit log of users with temporary elevated privileges and the operation(s) they performed is essential to reporting. Administrators will want to correlate the events written to the audit trail with the records written to sudo's logfile to verify if unauthorized commands have been executed. Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised information system accounts, is a serious and ongoing concern and can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider threats and the advanced persistent threat.
5.2.3.3 Record Attempts to perform maintenance activities The Red Hat Enterprise Linux 8 operating system must generate audit records for privileged activities, nonlocal maintenance, diagnostic sessions and other system-level access. Verify the operating system audits activities performed during nonlocal maintenance and diagnostic sessions. Run the following command: 
$ sudo auditctl -l | grep sudo.log
-w /var/log/sudo.log -p wa -k maintenance
 If events associated with nonlocal administrative access or diagnostic sessions are not logged, a major tool for assessing and investigating attacks would not be available. This requirement addresses auditing-related issues associated with maintenance tools used specifically for diagnostic and repair actions on organizational information systems. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. This requirement applies to hardware/software diagnostic test equipment or tools. This requirement does not cover hardware/software components that may support information system maintenance, yet are a part of the system, for example, the software implementing "ping," "ls," "ipconfig," or the hardware and software implementing the monitoring port of an Ethernet switch.
5.2.3.4 Record Attempts to Alter the localtime File If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-w /etc/localtime -p wa -k audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-w /etc/localtime -p wa -k audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used. 		Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
5.2.3.4 Record attempts to alter time through adjtimex If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rules
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rules
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: 
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules
 Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
5.2.3.4 Record Attempts to Alter Time Through stime If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d for both 32 bit and 64 bit systems: 
-a always,exit -F arch=b32 -S stime -F key=audit_time_rules
Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file for both 32 bit and 64 bit systems: 
-a always,exit -F arch=b32 -S stime -F key=audit_time_rules
Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined system calls: 
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules
 Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
5.2.3.4 Record attempts to alter time through settimeofday If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rules
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rules
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: 
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules
 Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
5.2.3.4 Record Attempts to Alter Time Through clock_settime If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls: 
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules
 Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.
5.2.3.5 Record Events that Modify the System's Network Environment If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification
-w /etc/issue -p wa -k audit_rules_networkconfig_modification
-w /etc/issue.net -p wa -k audit_rules_networkconfig_modification
-w /etc/hosts -p wa -k audit_rules_networkconfig_modification
-w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S sethostname,setdomainname -F key=audit_rules_networkconfig_modification
-w /etc/issue -p wa -k audit_rules_networkconfig_modification
-w /etc/issue.net -p wa -k audit_rules_networkconfig_modification
-w /etc/hosts -p wa -k audit_rules_networkconfig_modification
-w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification
 The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited.
5.2.3.5 Record Events that Modify the System's Network Environment If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-w /etc/sysconfig/network-scripts -p wa -k audit_rules_networkconfig_modification_network_scripts
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-w /etc/sysconfig/network-scripts -p wa -k audit_rules_networkconfig_modification_network_scripts
 The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited.
5.2.3.6 Ensure auditd Collects Information on the Use of Privileged Commands The audit system should collect information about usage of privileged commands for all users. These are commands with suid or sgid bits on and they are specially risky in local block device partitions not mounted with noexec and nosuid options. Therefore, these partitions should be first identified by the following command: 
findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,) | grep -Pv "noexec|nosuid"
For all partitions listed by the previous command, it is necessary to search for setuid / setgid programs using the following command: 
$ sudo find PARTITION -xdev -perm /6000 -type f 2>/dev/null
For each setuid / setgid program identified by the previous command, an audit rule must be present in the appropriate place using the following line structure: 
-a always,exit -F path=PROG_PATH -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup, add the line to a file with suffix .rules in the /etc/audit/rules.d directory, replacing the PROG_PATH part with the full path of that setuid / setgid identified program. If the auditd daemon is configured to use the auditctl utility instead, add the line to the /etc/audit/audit.rules file, also replacing the PROG_PATH part with the full path of that setuid / setgid identified program. 		Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised system accounts, is a serious and ongoing concern that can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider and advanced persistent threats.

Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.
5.2.3.7 Record Unsuccessful Access Attempts to Files - openat At a minimum, the audit system should collect unauthorized file accesses for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S openat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S openat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
 Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
5.2.3.7 Record Unsuccessful Access Attempts to Files - open At a minimum, the audit system should collect unauthorized file accesses for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S open -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S open -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
 Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
5.2.3.7 Record Unsuccessful Access Attempts to Files - creat At a minimum, the audit system should collect unauthorized file accesses for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S creat -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S creat -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
 Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
5.2.3.7 Record Unsuccessful Access Attempts to Files - ftruncate At a minimum, the audit system should collect unauthorized file accesses for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
 Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
5.2.3.7 Record Unsuccessful Access Attempts to Files - truncate At a minimum, the audit system should collect unauthorized file accesses for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b32 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
If the system is 64 bit then also add the following lines: 
-a always,exit -F arch=b64 -S truncate -F exit=-EACCES -F auid>=1000 -F auid!=unset -F key=access
-a always,exit -F arch=b64 -S truncate -F exit=-EPERM -F auid>=1000 -F auid!=unset -F key=access
 Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.
5.2.3.8 Record Events that Modify User/Group Information - /etc/security/opasswd If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, in order to capture events that modify account changes: 

-w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: 

-w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification
 In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
5.2.3.8 Record Events that Modify User/Group Information - /etc/shadow If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, in order to capture events that modify account changes: 

-w /etc/shadow -p wa -k audit_rules_usergroup_modification


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: 

-w /etc/shadow -p wa -k audit_rules_usergroup_modification
 In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
5.2.3.8 Record Events that Modify User/Group Information - /etc/group If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, in order to capture events that modify account changes: 

-w /etc/group -p wa -k audit_rules_usergroup_modification


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: 

-w /etc/group -p wa -k audit_rules_usergroup_modification
 In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
5.2.3.8 Record Events that Modify User/Group Information - /etc/passwd If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, in order to capture events that modify account changes: 

-w /etc/passwd -p wa -k audit_rules_usergroup_modification


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: 

-w /etc/passwd -p wa -k audit_rules_usergroup_modification
 In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
5.2.3.8 Record Events that Modify User/Group Information - /etc/gshadow If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d, in order to capture events that modify account changes: 

-w /etc/gshadow -p wa -k audit_rules_usergroup_modification


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file, in order to capture events that modify account changes: 

-w /etc/gshadow -p wa -k audit_rules_usergroup_modification
 In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - chmod At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fchown At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - setxattr At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S setxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S setxattr -F auid=0 -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S setxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S setxattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fchownat At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - chown At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fchmodat At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - lremovexattr At a minimum, the audit system should collect file permission changes for all users and root.

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S lremovexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S lremovexattr -F auid=0 -F key=perm_mod


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S lremovexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S lremovexattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - lsetxattr At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S lsetxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S lsetxattr -F auid=0 -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S lsetxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S lsetxattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fsetxattr At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S fsetxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S fsetxattr -F auid=0 -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S fsetxattr -F auid=0 -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S fsetxattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - removexattr At a minimum, the audit system should collect file permission changes for all users and root.

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S removexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S removexattr -F auid=0 -F key=perm_mod


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S removexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S removexattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fchmod At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - lchown At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod
If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=unset -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.9 Record Events that Modify the System's Discretionary Access Controls - fremovexattr At a minimum, the audit system should collect file permission changes for all users and root.

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S fremovexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S fremovexattr -F auid=0 -F key=perm_mod


If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b32 -S fremovexattr -F auid=0 -F key=perm_mod


If the system is 64 bit then also add the following line: 
-a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod
-a always,exit -F arch=b64 -S fremovexattr -F auid=0 -F key=perm_mod
 The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.
5.2.3.10 Ensure auditd Collects Information on Exporting to Media (successful) At a minimum, the audit system should collect media exportation events for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=export
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=unset -F key=export
 The unauthorized exportation of data to external media could result in an information leak where classified information, Privacy Act information, and intellectual property could be lost. An audit trail should be created each time a filesystem is mounted to help identify and guard against information loss.
5.2.3.11 Record Attempts to Alter Process and Session Initiation Information The audit system already collects process information for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d in order to watch for attempted manual edits of files involved in storing such process information: 
-w /var/run/utmp -p wa -k session
-w /var/log/btmp -p wa -k session
-w /var/log/wtmp -p wa -k session
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for attempted manual edits of files involved in storing such process information: 
-w /var/run/utmp -p wa -k session
-w /var/log/btmp -p wa -k session
-w /var/log/wtmp -p wa -k session
 Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion.
5.2.3.12 Record Attempts to Alter Logon and Logout Events - faillock The audit system already collects login information for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d in order to watch for attempted manual edits of files involved in storing logon events: 
-w /var/log/faillock -p wa -k logins
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: 
-w /var/log/faillock -p wa -k logins
 Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion.
5.2.3.12 Record Attempts to Alter Logon and Logout Events - lastlog The audit system already collects login information for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d in order to watch for attempted manual edits of files involved in storing logon events: 
-w /var/log/lastlog -p wa -k logins
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to watch for unattempted manual edits of files involved in storing logon events: 
-w /var/log/lastlog -p wa -k logins
 Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion.
5.2.3.13 Ensure auditd Collects File Deletion Events by User - unlink At a minimum, the audit system should collect file deletion events for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=delete
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S unlink -F auid>=1000 -F auid!=unset -F key=delete
 Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence.
5.2.3.13 Ensure auditd Collects File Deletion Events by User - unlinkat At a minimum, the audit system should collect file deletion events for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=delete
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S unlinkat -F auid>=1000 -F auid!=unset -F key=delete
 Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence.
5.2.3.13 Ensure auditd Collects File Deletion Events by User - renameat At a minimum, the audit system should collect file deletion events for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=delete
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S renameat -F auid>=1000 -F auid!=unset -F key=delete
 Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence.
5.2.3.13 Ensure auditd Collects File Deletion Events by User - rename At a minimum, the audit system should collect file deletion events for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=delete
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S rename -F auid>=1000 -F auid!=unset -F key=delete
 Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence.
5.2.3.14 Record Events that Modify the System's Mandatory Access Controls in usr/share If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-w /usr/share/selinux/ -p wa -k MAC-policy
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-w /usr/share/selinux/ -p wa -k MAC-policy
 The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited.
5.2.3.14 Record Events that Modify the System's Mandatory Access Controls If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d: 
-w /etc/selinux/ -p wa -k MAC-policy
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file: 
-w /etc/selinux/ -p wa -k MAC-policy
 The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited.
5.2.3.15 Record Any Attempts to Run chcon At a minimum, the audit system should collect any execution attempt of the chcon command for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/bin/chcon -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F path=/usr/bin/chcon -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
 Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised system accounts, is a serious and ongoing concern and can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider and advanced persistent threats.

Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.
5.2.3.16 Record Any Attempts to Run setfacl At a minimum, the audit system should collect any execution attempt of the setfacl command for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F path=/usr/bin/setfacl -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
 Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the information system (e.g., module or policy filter).
5.2.3.17 Record Any Attempts to Run chacl At a minimum, the audit system should collect any execution attempt of the chacl command for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/bin/chacl -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file: 
-a always,exit -F path=/usr/bin/chacl -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
 Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the information system (e.g., module or policy filter).
5.2.3.18 Ensure auditd Collects Information on the Use of Privileged Commands - usermod At a minimum, the audit system should collect the execution of privileged commands for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add a line of the following form to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/sbin/usermod -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: 
-a always,exit -F path=/usr/sbin/usermod -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
 Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised system accounts, is a serious and ongoing concern and can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider and advanced persistent threats.

Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.
5.2.3.19 Ensure auditd Collects Information on the Use of Privileged Commands - kmod At a minimum, the audit system should collect the execution of privileged commands for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add a line of the following form to a file with suffix .rules in the directory /etc/audit/rules.d: 
-a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add a line of the following form to /etc/audit/audit.rules: 
-a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=unset -F key=privileged
 Without generating audit records that are specific to the security and mission needs of the organization, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one. Audit records can be generated from various components within the information system (e.g., module or policy filter).
5.2.3.19 Ensure auditd Collects Information on Kernel Module Loading and Unloading - finit_module If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S finit_module -F auid>=1000 -F auid!=unset -F key=modules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to capture 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.
5.2.3.19 Ensure auditd Collects Information on Kernel Module Unloading - create_module To capture kernel module unloading events, use following line, setting ARCH to either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit: 
-a always,exit -F arch=ARCH -S create_module -F key=module-change
Place 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.
5.2.3.19 Ensure auditd Collects Information on Kernel Module Unloading - delete_module To capture kernel module unloading events, use following line, setting ARCH to either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit: 
-a always,exit -F arch=ARCH -S delete_module -F auid>=1000 -F auid!=unset -F key=modules
Place 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.
5.2.3.19 Ensure auditd Collects Information on Kernel Module Loading - init_module To capture kernel module loading events, use following line, setting ARCH to either b32 for 32-bit system, or having two lines for both b32 and b64 in case your system is 64-bit: 
-a always,exit -F arch=ARCH -S init_module -F auid>=1000 -F auid!=unset -F key=modules
Place 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.
5.2.3.19 Ensure auditd Collects Information on Kernel Module Loading and Unloading - query_module If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following lines to a file with suffix .rules in the directory /etc/audit/rules.d to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system: 
-a always,exit -F arch=ARCH -S query_module -F auid>=1000 -F auid!=unset -F key=modules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following lines to /etc/audit/audit.rules file in order to capture 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.
5.2.3.20 Make the auditd Configuration Immutable If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d in order to make the auditd configuration immutable: 
-e 2
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file in order to make the auditd configuration immutable: 
-e 2
With this setting, a reboot will be required to change any audit rules. 		Making the audit configuration immutable prevents accidental as well as malicious modification of the audit rules, although it may be problematic if legitimate changes are needed during system operation.
5.2.4.1 System Audit Logs Must Have Mode 0750 or Less Permissive Verify the audit log directories have a mode of "0700" or less permissive by first determining where the audit logs are stored with the following command: 
$ sudo grep -iw log_file /etc/audit/auditd.conf

log_file = /var/log/audit/audit.log
Configure the audit log directory to be protected from unauthorized read access by setting the correct permissive mode with the following command: 
$ sudo chmod 0700 audit_log_directory
By default, audit_log_directory is "/var/log/audit". 		If users can write to audit logs, audit trails can be modified or destroyed.
5.2.4.2 System Audit Logs Must Have Mode 0640 or Less Permissive Determine where the audit logs are stored with the following command: 
$ sudo grep -iw log_file /etc/audit/auditd.conf
log_file = /var/log/audit/audit.log
Configure the audit log to be protected from unauthorized read access by setting the correct permissive mode with the following command: 
$ sudo chmod 0600 audit_log_file
By default, audit_log_file is "/var/log/audit/audit.log". 		If users can write to audit logs, audit trails can be modified or destroyed.
5.2.4.3 System Audit Logs Must Be Owned By Root All audit logs must be owned by root user. The path for audit log can be configured via log_file parameter in 
/etc/audit/auditd.conf
or by default, the path for audit log is 
/var/log/audit/
. To properly set the owner of /var/log/audit/*, run the command: 
$ sudo chown root /var/log/audit/*
Unauthorized disclosure of audit records can reveal system and configuration data to attackers, thus compromising its confidentiality.
5.2.4.4 System Audit Logs Must Be Group Owned By Root All audit logs must be group owned by root user. The path for audit log can be configured via log_file parameter in 
/etc/audit/auditd.conf
or, by default, the path for audit log is 
/var/log/audit/
. To properly set the group owner of /var/log/audit/*, run the command: 
$ sudo chgrp root /var/log/audit/*
If log_group in /etc/audit/auditd.conf is set to a group other than the root group account, change the group ownership of the audit logs to this specific group. 		Unauthorized disclosure of audit records can reveal system and configuration data to attackers, thus compromising its confidentiality.
5.2.4.5 Audit Configuration Files Permissions are 640 or More Restrictive All audit configuration files permissions must be 640 or more restrictive. 
chmod 0640 /etc/audit/audit*.{rules,conf} /etc/audit/rules.d/*
 Without the capability to restrict which roles and individuals can select which events are audited, unauthorized personnel may be able to prevent the auditing of critical events. Misconfigured audits may degrade the system's performance by overwhelming the audit log. Misconfigured audits may also make it more difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.
5.2.4.6 Audit Configuration Files Must Be Owned By Root All audit configuration files must be owned by root user. To properly set the owner of /etc/audit/, run the command: 
$ sudo chown root /etc/audit/
To properly set the owner of /etc/audit/rules.d/, run the command: 
$ sudo chown root /etc/audit/rules.d/
Without the capability to restrict which roles and individuals can select which events are audited, unauthorized personnel may be able to prevent the auditing of critical events. Misconfigured audits may degrade the system's performance by overwhelming the audit log. Misconfigured audits may also make it more difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.
5.2.4.7 Audit Configuration Files Must Be Owned By Group root All audit configuration files must be owned by group root. 
chown :root /etc/audit/audit*.{rules,conf} /etc/audit/rules.d/*
 Without the capability to restrict which roles and individuals can select which events are audited, unauthorized personnel may be able to prevent the auditing of critical events. Misconfigured audits may degrade the system's performance by overwhelming the audit log. Misconfigured audits may also make it more difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.
5.2.4.8 Verify that audit tools Have Mode 0755 or less The Red Hat Enterprise Linux 8 operating system audit tools must have the proper permissions configured to protected against unauthorized access. Verify it by running the following command: 
$ stat -c "%n %a" /sbin/auditctl /sbin/aureport /sbin/ausearch /sbin/autrace /sbin/auditd /sbin/audispd /sbin/augenrules

/sbin/auditctl 755
/sbin/aureport 755
/sbin/ausearch 755
/sbin/autrace 755
/sbin/auditd 755
/sbin/audispd 755
/sbin/augenrules 755
Audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators 		Protecting audit information also includes identifying and protecting the tools used to view and manipulate log data. Therefore, protecting audit tools is necessary to prevent unauthorized operation on audit information. Operating systems providing tools to interface with audit information will leverage user permissions and roles identifying the user accessing the tools and the corresponding rights the user enjoys to make access decisions regarding the access to audit tools.
5.2.4.9 Verify that audit tools are owned by root The Red Hat Enterprise Linux 8 operating system audit tools must have the proper ownership configured to protected against unauthorized access. Verify it by running the following command: 
$ stat -c "%n %U" /sbin/auditctl /sbin/aureport /sbin/ausearch /sbin/autrace /sbin/auditd /sbin/audispd /sbin/augenrules

/sbin/auditctl root
/sbin/aureport root
/sbin/ausearch root
/sbin/autrace root
/sbin/auditd root
/sbin/audispd root
/sbin/augenrules root
Audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators 		Protecting audit information also includes identifying and protecting the tools used to view and manipulate log data. Therefore, protecting audit tools is necessary to prevent unauthorized operation on audit information. Operating systems providing tools to interface with audit information will leverage user permissions and roles identifying the user accessing the tools and the corresponding rights the user enjoys to make access decisions regarding the access to audit tools.
5.2.4.10 Verify that audit tools are owned by group root The Red Hat Enterprise Linux 8 operating system audit tools must have the proper ownership configured to protected against unauthorized access. Verify it by running the following command: 
$ stat -c "%n %G" /sbin/auditctl /sbin/aureport /sbin/ausearch /sbin/autrace /sbin/auditd /sbin/audispd /sbin/augenrules

/sbin/auditctl root
/sbin/aureport root
/sbin/ausearch root
/sbin/autrace root
/sbin/auditd root
/sbin/audispd root
/sbin/augenrules root
Audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators 		Protecting audit information also includes identifying and protecting the tools used to view and manipulate log data. Therefore, protecting audit tools is necessary to prevent unauthorized operation on audit information. Operating systems providing tools to interface with audit information will leverage user permissions and roles identifying the user accessing the tools and the corresponding rights the user enjoys to make access decisions regarding the access to audit tools.
5.3.1 Build and Test AIDE Database Run the following command to generate a new database: 
$ sudo /usr/sbin/aide --init
By default, the database will be written to the file /var/lib/aide/aide.db.new.gz. Storing the database, the configuration file /etc/aide.conf, and the binary /usr/sbin/aide (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows: 
$ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
To initiate a manual check, run the following command: 
$ sudo /usr/sbin/aide --check
If this check produces any unexpected output, investigate. 		For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files.
5.3.1 Install AIDE The aide package can be installed with the following command: 
$ sudo yum install aide
 The AIDE package must be installed if it is to be available for integrity checking.
5.3.2 Configure Periodic Execution of AIDE At a minimum, AIDE should be configured to run a weekly scan. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 
05 4 * * * root /usr/sbin/aide --check
To implement a weekly execution of AIDE at 4:05am using cron, add the following line to /etc/crontab: 
05 4 * * 0 root /usr/sbin/aide --check
AIDE can be executed periodically through other means; this is merely one example. The usage of cron's special time codes, such as @daily and @weekly is acceptable. 		By default, AIDE does not install itself for periodic execution. Periodically running AIDE is necessary to reveal unexpected changes in installed files.

Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.

Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.
5.3.3 Configure AIDE to Verify the Audit Tools The operating system file integrity tool must be configured to protect the integrity of the audit tools. Protecting the integrity of the tools used for auditing purposes is a critical step toward ensuring the integrity of audit information. Audit information includes all information (e.g., audit records, audit settings, and audit reports) needed to successfully audit information system activity. Audit tools include but are not limited to vendor-provided and open-source audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators. It is not uncommon for attackers to replace the audit tools or inject code into the existing tools to provide the capability to hide or erase system activity from the audit logs. To address this risk, audit tools must be cryptographically signed to provide the capability to identify when the audit tools have been modified, manipulated, or replaced. An example is a checksum hash of the file or files.
6.1.1 Verify User Who Owns passwd File To properly set the owner of /etc/passwd, run the command: 
$ sudo chown root /etc/passwd
The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security.
6.1.1 Verify Permissions on passwd File To properly set the permissions of /etc/passwd, run the command: 
$ sudo chmod 0644 /etc/passwd
 If the /etc/passwd file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security.
6.1.1 Verify Group Who Owns passwd File To properly set the group owner of /etc/passwd, run the command: 
$ sudo chgrp root /etc/passwd
 The /etc/passwd file contains information about the users that are configured on the system. Protection of this file is critical for system security.
6.1.2 Verify Group Who Owns Backup passwd File To properly set the group owner of /etc/passwd-, run the command: 
$ sudo chgrp root /etc/passwd-
 The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security.
6.1.2 Verify Permissions on Backup passwd File To properly set the permissions of /etc/passwd-, run the command: 
$ sudo chmod 0644 /etc/passwd-
 The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security.
6.1.2 Verify User Who Owns Backup passwd File To properly set the owner of /etc/passwd-, run the command: 
$ sudo chown root /etc/passwd-
The /etc/passwd- file is a backup file of /etc/passwd, and as such, it contains information about the users that are configured on the system. Protection of this file is critical for system security.
6.1.3 Verify Permissions and Ownership of Old Passwords File To properly set the owner of /etc/security/opasswd, run the command: 
$ sudo chown root /etc/security/opasswd
To properly set the group owner of /etc/security/opasswd, run the command: 
$ sudo chgrp root /etc/security/opasswd
To properly set the permissions of /etc/security/opasswd, run the command: 
$ sudo chmod 0600 /etc/security/opasswd
 The /etc/security/opasswd file stores old passwords to prevent password reuse. Protection of this file is critical for system security.
6.1.4 Verify User Who Owns group File To properly set the owner of /etc/group, run the command: 
$ sudo chown root /etc/group
The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.4 Verify Group Who Owns group File To properly set the group owner of /etc/group, run the command: 
$ sudo chgrp root /etc/group
 The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.4 Verify Permissions on group File To properly set the permissions of /etc/group, run the command: 
$ sudo chmod 0644 /etc/group
 The /etc/group file contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.5 Verify Permissions on Backup group File To properly set the permissions of /etc/group-, run the command: 
$ sudo chmod 0644 /etc/group-
 The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.5 Verify Group Who Owns Backup group File To properly set the group owner of /etc/group-, run the command: 
$ sudo chgrp root /etc/group-
 The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.5 Verify User Who Owns Backup group File To properly set the owner of /etc/group-, run the command: 
$ sudo chown root /etc/group-
The /etc/group- file is a backup file of /etc/group, and as such, it contains information regarding groups that are configured on the system. Protection of this file is important for system security.
6.1.6 Verify User Who Owns shadow File To properly set the owner of /etc/shadow, run the command: 
$ sudo chown root /etc/shadow
The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
6.1.6 Verify Permissions on shadow File To properly set the permissions of /etc/shadow, run the command: 
$ sudo chmod 0000 /etc/shadow
 The /etc/shadow file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.
6.1.6 Verify Group Who Owns shadow File To properly set the group owner of /etc/shadow, run the command: 
$ sudo chgrp root /etc/shadow
 The /etc/shadow file stores password hashes. Protection of this file is critical for system security.
6.1.7 Verify Group Who Owns Backup shadow File To properly set the owner of /etc/shadow-, run the command: 
$ sudo chown root /etc/shadow-
The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security.
6.1.7 Verify Permissions on Backup shadow File To properly set the permissions of /etc/shadow-, run the command: 
$ sudo chmod 0000 /etc/shadow-
 The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security.
6.1.7 Verify User Who Owns Backup shadow File To properly set the group owner of /etc/shadow-, run the command: 
$ sudo chgrp root /etc/shadow-
 The /etc/shadow- file is a backup file of /etc/shadow, and as such, it contains the list of local system accounts and password hashes. Protection of this file is critical for system security.
6.1.8 Verify Group Who Owns gshadow File To properly set the group owner of /etc/gshadow, run the command: 
$ sudo chgrp root /etc/gshadow
 The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
6.1.8 Verify User Who Owns gshadow File To properly set the owner of /etc/gshadow, run the command: 
$ sudo chown root /etc/gshadow
The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
6.1.8 Verify Permissions on gshadow File To properly set the permissions of /etc/gshadow, run the command: 
$ sudo chmod 0000 /etc/gshadow
 The /etc/gshadow file contains group password hashes. Protection of this file is critical for system security.
6.1.9 Verify User Who Owns Backup gshadow File To properly set the owner of /etc/gshadow-, run the command: 
$ sudo chown root /etc/gshadow-
The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security.
6.1.9 Verify Permissions on Backup gshadow File To properly set the permissions of /etc/gshadow-, run the command: 
$ sudo chmod 0000 /etc/gshadow-
 The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security.
6.1.9 Verify Group Who Owns Backup gshadow File To properly set the group owner of /etc/gshadow-, run the command: 
$ sudo chgrp root /etc/gshadow-
 The /etc/gshadow- file is a backup of /etc/gshadow, and as such, it contains group password hashes. Protection of this file is critical for system security.
6.1.10 Verify Group Who Owns /etc/shells File To properly set the group owner of /etc/shells, run the command: 
$ sudo chgrp root /etc/shells
 The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected.
6.1.10 Verify Who Owns /etc/shells File To properly set the owner of /etc/shells, run the command: 
$ sudo chown root /etc/shells
The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected.
6.1.10 Verify Permissions on /etc/shells File To properly set the permissions of /etc/shells, run the command: 
$ sudo chmod 0644 /etc/shells
 The /etc/shells file contains the list of full pathnames to shells on the system. Since this file is used by many system programs this file should be protected.
6.1.11 Verify that All World-Writable Directories Have Sticky Bits Set When the so-called 'sticky bit' is set on a directory, only the owner of a given file may remove that file from the directory. Without the sticky bit, any user with write access to a directory may remove any file in the directory. Setting the sticky bit prevents users from removing each other's files. In cases where there is no reason for a directory to be world-writable, a better solution is to remove that permission rather than to set the sticky bit. However, if a directory is used by a particular application, consult that application's documentation instead of blindly changing modes.
To set the sticky bit on a world-writable directory DIR, run the following command: 
$ sudo chmod +t DIR
 Failing to set the sticky bit on public directories allows unauthorized users to delete files in the directory structure.

The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, by users for temporary file storage (such as /tmp), and for directories requiring global read/write access.
6.1.11 Ensure No World-Writable Files Exist It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account. Finally, this applies to real files and not virtual files that are a part of pseudo file systems such as sysfs or procfs. Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files.
6.1.12 Ensure All Files Are Owned by a User If any files are not owned by a user, then the cause of their lack of ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate user. Locate the mount points related to local devices by the following command: 
$ findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,)
For all mount points listed by the previous command, it is necessary to search for files which do not belong to a valid user using the following command: 
$ sudo find MOUNTPOINT -xdev -nouser 2>/dev/null
 Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account, or other similar cases. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.
6.1.12 Ensure All Files Are Owned by a Group If any file is not group-owned by a group present in /etc/group, the cause of the lack of group-ownership must be investigated. Following this, those files should be deleted or assigned to an appropriate group. Locate the mount points related to local devices by the following command: 
$ findmnt -n -l -k -it $(awk '/nodev/ { print $2 }' /proc/filesystems | paste -sd,)
For all mount points listed by the previous command, it is necessary to search for files which do not belong to a valid group using the following command: 
$ sudo find MOUNTPOINT -xdev -nogroup 2>/dev/null
 Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account, or other similar cases. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.
6.2.1 Verify All Account Password Hashes are Shadowed If any password hashes are stored in /etc/passwd (in the second field, instead of an x or *), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely. The hashes for all user account passwords should be stored in the file /etc/shadow and never in /etc/passwd, which is readable by all users.
6.2.2 Ensure There Are No Accounts With Blank or Null Passwords Check the "/etc/shadow" file for blank passwords with the following command: 
$ sudo awk -F: '!$2 {print $1}' /etc/shadow
If the command returns any results, this is a finding. Configure all accounts on the system to have a password or lock the account with the following commands: Perform a password reset: 
$ sudo passwd [username]
Lock an account: 
$ sudo passwd -l [username]
 If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.
6.2.3 All GIDs referenced in /etc/passwd must be defined in /etc/group Add a group to the system for each GID referenced without a corresponding group. If a user is assigned the Group Identifier (GID) of a group not existing on the system, and a group with the Group Identifier (GID) is subsequently created, the user may have unintended rights to any files associated with the group.
6.2.4 Ensure All Accounts on the System Have Unique User IDs Change user IDs (UIDs), or delete accounts, so each has a unique name. To assure accountability and prevent unauthenticated access, interactive users must be identified and authenticated to prevent potential misuse and compromise of the system.
6.2.5 Ensure All Groups on the System Have Unique Group ID Change the group name or delete groups, so each has a unique id. To assure accountability and prevent unauthenticated access, groups must be identified uniquely to prevent potential misuse and compromise of the system.
6.2.6 Ensure All Accounts on the System Have Unique Names Ensure accounts on the system have unique names. To ensure all accounts have unique names, run the following command: 
$ sudo getent passwd | awk -F: '{ print $1}' | uniq -d
If a username is returned, change or delete the username. 		Unique usernames allow for accountability on the system.
6.2.7 Ensure All Groups on the System Have Unique Group Names Change the group name or delete groups, so each has a unique name. To assure accountability and prevent unauthenticated access, groups must be identified uniquely to prevent potential misuse and compromise of the system.
6.2.8 Ensure that Root's Path Does Not Include World or Group-Writable Directories For each element in root's path, run: 
# ls -ld DIR
and ensure that write permissions are disabled for group and other. 		Such entries increase the risk that root could execute code provided by unprivileged users, and potentially malicious code.
6.2.8 Ensure that Root's Path Does Not Include Relative Paths or Null Directories Ensure that none of the directories in root's path is equal to a single . character, or that it contains any instances that lead to relative path traversal, such as .. or beginning a path without the slash (/) character. Also ensure that there are no "empty" elements in the path, such as in these examples: 
PATH=:/bin
PATH=/bin:
PATH=/bin::/sbin
These empty elements have the same effect as a single . character. 		Including these entries increases the risk that root could execute code from an untrusted location.
6.2.9 Verify Only Root Has UID 0 If any account other than root has a UID of 0, this misconfiguration should be investigated and the accounts other than root should be removed or have their UID changed.
If the account is associated with system commands or applications the UID should be changed to one greater than "0" but less than "1000." Otherwise assign a UID greater than "1000" that has not already been assigned. 		An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner.
6.2.10 All Interactive User Home Directories Must Be Owned By The Primary User Change the owner of interactive users home directories to that correct owner. To change the owner of a interactive users home directory, use the following command: 
$ sudo chown USER /home/USER
This rule ensures every home directory related to an interactive user is owned by an interactive user. It also ensures that interactive users are owners of one and only one home directory. 		If a local interactive user does not own their home directory, unauthorized users could access or modify the user's files, and the users may not be able to access their own files.
6.2.10 All Interactive Users Home Directories Must Exist Create home directories to all local interactive users that currently do not have a home directory assigned. Use the following commands to create the user home directory assigned in /etc/passwd: 
$ sudo mkdir /home/USER
 If a local interactive user has a home directory defined that does not exist, the user may be given access to the / directory as the current working directory upon logon. This could create a Denial of Service because the user would not be able to access their logon configuration files, and it may give them visibility to system files they normally would not be able to access.
6.2.10 All Interactive User Home Directories Must Have mode 0750 Or Less Permissive Change the mode of interactive users home directories to 0750. To change the mode of interactive users home directory, use the following command: 
$ sudo chmod 0750 /home/USER
 Excessive permissions on local interactive user home directories may allow unauthorized access to user files by other users.
6.2.11 Verify No .forward Files Exist The .forward file specifies an email address to forward the user's mail to. Use of the .forward file poses a security risk in that sensitive data may be inadvertently transferred outside the organization. The .forward file also poses a risk as it can be used to execute commands that may perform unintended actions.
6.2.11 Ensure users' .netrc Files are not group or world accessible While the system administrator can establish secure permissions for users' .netrc files, the users can easily override these. This rule ensures every .netrc file or directory under the home directory related to an interactive user is not group or world accessible .netrc files may contain unencrypted passwords that may be used to attack other systems. Note: While the complete removal of .netrc files is recommended, if any are required on the system, secure permissions must be applied.
6.2.11 Remove Rsh Trust Files The files /etc/hosts.equiv and ~/.rhosts (in each user's home directory) list remote hosts and users that are trusted by the local system when using the rshd daemon. To remove these files, run the following command to delete them from any location: 
$ sudo rm /etc/hosts.equiv
$ rm ~/.rhosts
 This action is only meaningful if .rhosts support is permitted through PAM. Trust files are convenient, but when used in conjunction with the R-services, they can allow unauthenticated access to a system.
6.2.11 User Initialization Files Must Be Group-Owned By The Primary Group Change the group owner of interactive users files to the group found in 
/etc/passwd
for the user. To change the group owner of a local interactive user home directory, use the following command: 
$ sudo chgrp USER_GROUP /home/USER/.INIT_FILE
This rule ensures every initialization file related to an interactive user is group-owned by an interactive user. 		Local initialization files for interactive users are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon.
6.2.11 Ensure All User Initialization Files Have Mode 0740 Or Less Permissive Set the mode of the user initialization files to 0740 with the following command: 
$ sudo chmod 0740 /home/USER/.INIT_FILE
 Local initialization files are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon.
6.2.11 User Initialization Files Must Be Owned By the Primary User Set the owner of the user initialization files for interactive users to the primary owner with the following command: 
$ sudo chown USER /home/USER/.*
This rule ensures every initialization file related to an interactive user is owned by an interactive user. 		Local initialization files are used to configure the user's shell environment upon logon. Malicious modification of these files could compromise accounts upon logon.
enable_authselect Enable authselect Configure user authentication setup to use the authselect tool. If authselect profile is selected, the rule will enable the minimal profile. Authselect is a successor to authconfig. It is a tool to select system authentication and identity sources from a list of supported profiles instead of letting the administrator manually build the PAM stack. That way, it avoids potential breakage of configuration, as it ships several tested profiles that are well tested and supported to solve different use-cases.
reload_dconf_db Make sure that the dconf databases are up-to-date with regards to respective keyfiles By default, DConf uses a binary database as a data backend. The system-level database is compiled from keyfiles in the /etc/dconf/db/ directory by the 
dconf update
command. More specifically, content present in the following directories: 
/etc/dconf/db/gdm.d
/etc/dconf/db/local.d
 Unlike text-based keyfiles, the binary database is impossible to check by OVAL. Therefore, in order to evaluate dconf configuration, both have to be true at the same time - configuration files have to be compliant, and the database needs to be more recent than those keyfiles, which gives confidence that it reflects them.