SV-271869r1092319: OL 9 must prevent IPv4 Internet Control Message Protocol (ICMP) redirect messages from being accepted. | Oracle Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

OL 9 must prevent IPv4 Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Description

Discussion Text

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack. This feature of the IPv4 protocol has few legitimate uses. It must be disabled unless absolutely required.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000366

References

DPMS Target Oracle Linux 9 DISA DPMS Target Oracle Linux 9 5680

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.ol9os:def:271869
# OL 9 must prevent IPv4 Internet Control Message Protocol (ICMP) redirect messages from being accepted.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# net.ipv4.conf.default.accept_redirects setting in kernel is 0
# sysctl_object (sysctl_test)
test_1() {
  [ "$(cat /proc/sys/net/ipv4/conf/default/accept_redirects)" -eq 0 ]
}

if test_1; 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
# DISA STIG OL 9 ICMP redirect check
if [ ! -x "$(command -v sysctl)" ]; then echo "FAIL"; exit 1; fi
if [ ! -f "/etc/sysctl.d/99-sysctl.conf" ]; then echo "PASS"; exit 0; fi
if grep -q "^net.ipv4.conf.default.accept_redirects = 0$" "/etc/sysctl.d/99-sysctl.conf"; then echo "PASS"; exit 0; fi
echo "FAIL"; exit 1

Remediation

Configure OL 9 to prevent IPv4 ICMP redirect messages from being accepted.

Add or edit the following line in a single system configuration file in the "/etc/sysctl.d/" directory:

net.ipv4.conf.default.accept_redirects = 0

Load settings from all system configuration files with the following command:

$ sudo sysctl --system