Vulnerability Discussion

Restricting access to the kernel message buffer limits access only to root. This prevents attackers from gaining additional system information as a nonprivileged user.

Check

Verify Ubuntu 24.04 LTS is configured to restrict access to the kernel message buffer with the following command:

$ sysctl kernel.dmesg_restrict
kernel.dmesg_restrict = 1

If "kernel.dmesg_restrict" is not set to "1" or is missing, this is a finding.

Verify there are no configurations that enable the kernel dmesg function:

$ sudo grep -r kernel.dmesg_restrict /run/sysctl.d/* /etc/sysctl.d/* /usr/local/lib/sysctl.d/* /usr/lib/sysctl.d/* /lib/sysctl.d/* /etc/sysctl.conf 2> /dev/null
/etc/sysctl.d/10-kernel-hardening.conf:kernel.dmesg_restrict = 1

If any instance of "kernel.dmesg_restrict" is uncommented and set to "0", or if conflicting results are returned, this is a finding.

Fix

Configure Ubuntu 24.04 LTS to restrict access to the kernel message buffer.

Set the system to the required kernel parameter by adding or modifying the following line in /etc/sysctl.conf or a config file in the /etc/sysctl.d/ directory:

kernel.dmesg_restrict = 1

Remove any configurations that conflict with the above from the following locations:
/run/sysctl.d/
/etc/sysctl.d/
/usr/local/lib/sysctl.d/
/usr/lib/sysctl.d/
/lib/sysctl.d/
/etc/sysctl.conf

Reload settings from all system configuration files with the following command:

$ sudo sysctl --system