Ubuntu OS must restrict access to the kernel message buffer.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-275567	SRG-OS-000138-GPOS-00069	RIIM-OS-213010	SV-275567r1147751_rule	2025-10-02	1

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

ℹ️ Check
Verify Ubuntu OS is configured to restrict access to the kernel message buffer by using 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 -ir 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 "kernel.dmesg_restrict" is not set to "1", is commented out, is missing, or conflicting results are returned, this is a finding.

ℹ️ Check

Verify Ubuntu OS is configured to restrict access to the kernel message buffer by using 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 -ir 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 "kernel.dmesg_restrict" is not set to "1", is commented out, is missing, or conflicting results are returned, this is a finding.

✔️ Fix
Configure Ubuntu OS to restrict access to the kernel message buffer. Add or modify the following line in the "/etc/sysctl.conf" file: 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 by using the following command: $ sudo sysctl --system Note: This is set by default as part of the NetIM Ubuntu baseline.

✔️ Fix

Configure Ubuntu OS to restrict access to the kernel message buffer. Add or modify the following line in the "/etc/sysctl.conf" file: 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 by using the following command: $ sudo sysctl --system Note: This is set by default as part of the NetIM Ubuntu baseline.