SV-37639r1: The system must not be configured for network bridging. | Red Hat Enterprise Linux 5 Security Technical Implementation Guide

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Assessment Title

Rule Text

The system must not be configured for network bridging.

Description

Discussion Text

Some systems have the ability to bridge or switch frames (link-layer forwarding) between multiple interfaces. This can be useful in a variety of situations but, if enabled when not needed, has the potential to bypass network partitioning and security.

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

IA Controls

NIST SP 800-53

Not mappedCCI-001551

Additional Details

Responsibility

System Administrator

IA Controls

ECSC-1

References

DPMS Target Red Hat 5 DISA DPMS Target Red Hat 5 2154

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.fso.rhel11:def:247
# The system must not be configured for network bridging.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# file_object (file_test)
test_1() {
  ! ( test -e '/proc/sys/net/bridge' &>/dev/null )
}
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  ! ( grep -Pq '^bridge' '/proc/modules' &>/dev/null )
}

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.fso.rhel11:def:247

if [ ! -d "/proc/sys/net/bridge" ]; then echo "PASS"; exit 0; fi
if [ "$(grep -r 'bridge' /proc/modules | wc -l)" -eq 0 ]; then echo "PASS"; exit 0; fi
echo "FAIL"; exit 1

Remediation

Configure the system to not use bridging.
# rmmod bridge
Edit /etc/modprobe.conf and add a line such as "install bridge /bin/false" to prevent the loading of the bridge module.