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V-255907

CAT III (Low)

The Ubuntu operating system must restrict access to the kernel message buffer.

Rule ID

SV-255907r958524_rule

STIG

Canonical Ubuntu 18.04 LTS Security Technical Implementation Guide

Version

V2R15

CCIs

CCI-001090

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 Content

Verify the operating system is configured to restrict access to the kernel message buffer with the following commands:

     $ sudo sysctl kernel.dmesg_restrict
     kernel.dmesg_restrict = 1

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

Check that the configuration files are present to enable this kernel parameter:

     $ 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.conf:kernel.dmesg_restrict = 1
     /etc/sysctl.d/99-sysctl.conf:kernel.dmesg_restrict = 1

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

If conflicting results are returned, this is a finding.

Fix Text

Configure the operating system 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