SV-257948r1045004: RHEL 9 systems using Domain Name Servers (DNS) resolution must have at least two name servers configured. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 9 systems using Domain Name Servers (DNS) resolution must have at least two name servers configured.

Description

Discussion Text

To provide availability for name resolution services, multiple redundant name servers are mandated. A failure in name resolution could lead to the failure of security functions requiring name resolution, which may include time synchronization, centralized authentication, and remote system logging.

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

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:257948
# RHEL 9 systems using Domain Name Servers (DNS) resolution must have at least two name servers configured.
# 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:
#   - variable_object (variable_test) -- /etc/resolv.conf is configured with at least two name servers: no extractor for field "value"

# The system is not using DNS
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (sed -En 's/^\s*hosts:\s*(.*)$/\1/p' '/etc/nsswitch.conf') | grep -Pq '(^|\s)dns(\s|$)'
}
# The system is using DNS
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\s*hosts:\s*(.*)$/\1/p' '/etc/nsswitch.conf') | grep -Pq '(^|\s)dns(\s|$)'
}
# /etc/resolv.conf contains at least one nameserver entry
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  grep -Pq '^nameserver\s+(.*)$' '/etc/resolv.conf' &>/dev/null
}

if ( test_1 || ( test_2 && test_3 ) ); 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
# OVAL Definition: oval:mil.disa.stig.rhel9os:def:257948

if [ ! -f "/etc/nsswitch.conf" ]; then echo "PASS"; exit 0; fi
grep -q "^\\s*hosts:\\s.*dns.*" /etc/nsswitch.conf || { echo "FAIL"; exit 1; }
if [ ! -s "/etc/resolv.conf" ]; then echo "PASS"; exit 0; fi
dns_mode=$(nmcli general dns-mode 2>/dev/null)
if [ "$dns_mode" = "none" ]; then
    grep -q "^nameserver\\s.*" /etc/resolv.conf || { echo "FAIL"; exit 1; }
    grep -c "^nameserver\\s.*" /etc/resolv.conf | grep -q "^[2-]$" || { echo "FAIL"; exit 1; }
elif [ "$dns_mode" = "default" ]; then
    nmcli connection show --fields NAME,IPV4.DNS | awk '{if ($2 ~ /^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$/) print $1}' | while read -r conn; do nmcli connection show $conn | grep -q "^IP4.DNS=.*,.*" || { echo "FAIL"; exit 1; }; done
else
    echo "FAIL"; exit 1;
fi
echo "PASS"; exit 0

Remediation

Configure the operating system to use two or more name servers for DNS resolution based on the DNS mode of the system.
	
If the NetworkManager DNS mode is set to "none", add the following lines to "/etc/resolv.conf":
	
nameserver [name server 1]
nameserver [name server 2]
	
Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers.
	
If the NetworkManager DNS mode is set to "default", add two DNS servers to a NetworkManager connection using the following command:
	
$ nmcli connection modify [connection name] ipv4.dns [name server 1],[name server 2]
	
Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers. Replace [connection name] with a valid NetworkManager connection name on the system. Replace ipv4 with ipv6 if IPv6 DNS servers are used.