SV-270749r1137695: Ubuntu 24.04 LTS must restrict access to the kernel message buffer. | Canonical Ubuntu 24.04 LTS STIG SCAP Benchmark

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Assessment Title

Rule Text

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

Description

Discussion Text

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

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-001090

References

DPMS Target Canonical Ubuntu 24.04 LTS DISA DPMS Target Canonical Ubuntu 24.04 LTS 5673

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

#!/bin/bash
# Reconstructed from oval:mil.disa.stig.ubuntu2404os:def:270749
# Ubuntu 24.04 LTS must restrict access to the kernel message buffer.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.
#
# MANUAL REVIEW REQUIRED -- the module(s) below could not be reconstructed
# into working code from curated SCC reference data, and are excluded from
# the automated result:
#   - textfilecontent54_object (textfilecontent54_test) -- kernel.dmesg_restrict setting in sysctl configuration files is set to 1: <set> composition (base object oval:mil.disa.stig.ind:obj:23026900, oval:mil.disa.stig.ind:obj:23026901): member unresolved -- no extractor for field "subexpression"

# kernel.dmesg_restrict setting in kernel is 1
# sysctl_object (sysctl_test)
test_1() {
  [ "$(cat /proc/sys/kernel/dmesg_restrict)" -eq 1 ]
}

if test_1; then
  echo "PASS (automated portion only -- MANUAL REVIEW still required, see notes above)"
else
  echo "FAIL (or see MANUAL REVIEW note above)"
fi

Assessment Script Powered by AISandbox-executed

A standalone Shell script to assess this control automatically. Review before running it in your environment.

Syntax-checked and actually executed in an isolated sandbox (not the real system this checks) — confirmed to run without errors.

#!/bin/sh
# DISA STIG / SCAP compliance check for Ubuntu 24.04 LTS kernel message buffer access restriction
if [ ! -x "$(command -v sysctl)" ]; then echo "FAIL"; exit 1; fi
if [ ! $(sysctl -n kernel.dmesg_restrict 2>/dev/null | grep -q '^1$') ]; then echo "FAIL"; exit 1; fi
if [ ! -e /etc/sysctl.conf ] || ! grep -q '^\\s*kernel\\.dmesg_restrict\\s*=\\s*1\\s*$' /etc/sysctl.conf; then echo "FAIL"; exit 1; fi
for dir in /run/sysctl.d /etc/sysctl.d /usr/local/lib/sysctl.d /usr/lib/sysctl.d /lib/sysctl.d /etc; do
    for file in "$dir"/*; do
        if [ -e "$file" ] && ! grep -q '^\\s*kernel\\.dmesg_restrict\\s*=\\s*1\\s*$' "$file"; then echo "FAIL"; exit 1; fi
    done
done
echo "PASS"; exit 0

Remediation

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