SV-257949r1134947: RHEL 9 must configure a DNS processing mode in Network Manager. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 9 must configure a DNS processing mode in Network Manager.

Description

Discussion Text

To ensure that DNS resolver settings are respected, a DNS mode in Network Manager must be configured. The following are common DNS values in NetworkManager.conf [main]: - default: NetworkManager will update /etc/resolv.conf to reflect the nameservers provided by currently active connections. - none: NetworkManager will not modify /etc/resolv.conf. Used when DNS is managed manually or by another service. - systemd-resolved: Uses systemd-resolved to manage DNS. - dnsmasq: Enables the internal dnsmasq plugin.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000366

References

DPMS Target Red Hat Enterprise Linux 9 DISA DPMS Target Red Hat Enterprise Linux 9 5551

Checks

DISA STIG (Manual Reference)

Verify that RHEL 9 has a DNS mode configured in Network Manager.

$ NetworkManager --print-config
[main]
dns=none

If the dns key under main does not exist or is not set to "default", "none", or "systemd-resolved", this is a finding.

Note: If RHEL 9 is configured to use a DNS resolver other than Network Manager, the configuration must be documented and approved by the information system security officer (ISSO).

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.rhel9os:def:257949
# RHEL 9 must configure a DNS processing mode in Network Manager.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# DNS setting exists in NetworkManager.conf and is default or none
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  ( (sed -En 's/^dns=(\S*)\s*$/\1/p' '/etc/NetworkManager/NetworkManager.conf') | grep -qxF 'none' ) || ( (sed -En 's/^dns=(\S*)\s*$/\1/p' '/etc/NetworkManager/NetworkManager.conf') | grep -qxF 'default' ) || ( (sed -En 's/^dns=(\S*)\s*$/\1/p' '/etc/NetworkManager/NetworkManager.conf') | grep -qxF 'systemd-resolved' )
}
# DNS setting exists in NetworkManager.conf main section
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\[main\]((?:\r?\n(?:[^[\r\n].*)?)*)/\1/p' '/etc/NetworkManager/NetworkManager.conf') | grep -Pq '\ndns='
}

if ( test_1 && test_2 ); then
  echo "PASS"
else
  echo "FAIL"
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
# OVAL Definition: oval:mil.disa.stig.rhel9os:def:257949


if [ ! -f "/etc/NetworkManager/NetworkManager.conf" ]; then echo "PASS"; exit 0; fi

if grep -qE "^\\[main\\]" /etc/NetworkManager/NetworkManager.conf && \
    (grep -E "^\\s*dns=default" /etc/NetworkManager/NetworkManager.conf || \
    grep -E "^\\s*dns=none" /etc/NetworkManager/NetworkManager.conf || \
    grep -E "^\\s*dns=systemd-resolved" /etc/NetworkManager/NetworkManager.conf); then echo "PASS"; exit 0; fi

echo "FAIL"; exit 1

Remediation

Configure NetworkManager in RHEL 9 to use a DNS mode.

In "/etc/NetworkManager/NetworkManager.conf", add the following line in the "[main]" section:

dns = <dns processing mode>

Where <dns processing mode> is default, none, or systemd-resolved.

NetworkManager must be reloaded for the change to take effect.

$ sudo systemctl reload NetworkManager