SV-204616r991589: The Red Hat Enterprise Linux operating system must not allow interfaces to perform Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects by default. | Red Hat Enterprise Linux 7 STIG SCAP Benchmark

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Assessment Title

Rule Text

The Red Hat Enterprise Linux operating system must not allow interfaces to perform Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects by default.

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 contain information from the system's route table, possibly revealing portions of the network topology.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000366V-72291SV-86915

References

DPMS Target Red Hat Enterprise Linux 7 DISA DPMS Target Red Hat Enterprise Linux 7 2899

Checks

DISA STIG (Manual Reference)

Verify the system does not allow interfaces to perform IPv4 ICMP redirects by default.

     # grep -r net.ipv4.conf.default.send_redirects /run/sysctl.d/* /etc/sysctl.d/* /usr/local/lib/sysctl.d/* /usr/lib/sysctl.d/* /lib/sysctl.d/* /etc/sysctl.conf 2> /dev/null

If "net.ipv4.conf.default.send_redirects" is not configured in the "/etc/sysctl.conf" file or in any of the other sysctl.d directories, is commented out or does not have a value of "0", this is a finding.

Check that the operating system implements the "default send_redirects" variables with the following command:

     # /sbin/sysctl -a | grep net.ipv4.conf.default.send_redirects
     net.ipv4.conf.default.send_redirects = 0 

If the returned line does not have a value of "0", this is a finding.

If conflicting results are returned, this is a finding.

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.rhel7:def:281
# The Red Hat Enterprise Linux operating system must not allow interfaces to perform Internet Protocol version 4 (IPv4) Internet Control Message Protocol (ICMP) redirects by default.
# 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 static parameter net.ipv4.conf.default.send_redirects set to 0 in /etc/sysctl.conf, or any of the other sysctl.d directories, is set to 1, and nothing else, and there are no conflicting settings in other files: <set> composition (base object oval:mil.disa.stig.rhel7:obj:2275, oval:mil.disa.stig.rhel7:obj:20461601): member unresolved -- no extractor for field "subexpression"

# kernel runtime parameter net.ipv4.conf.default.send_redirects set to 0
# sysctl_object (sysctl_test)
test_2() {
  [ "$(cat /proc/sys/net/ipv4/conf/default/send_redirects)" -eq 0 ]
}

if test_2; 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:mil.disa.stig.rhel7:def:281

if [ ! -f "/etc/sysctl.conf" ]; then echo "PASS"; exit 0; fi
if grep -q "^[\\s]*net\\.ipv4\\.conf\\.default\\.send_redirects[\\s]*=[\\s]*0[\\s]*$" /etc/sysctl.conf; then echo "PASS"; exit 0; fi
if [ ! -d "/etc/sysctl.d" ]; then echo "PASS"; exit 0; fi
for file in /etc/sysctl.d/*.conf; do
    if grep -q "^[\\s]*net\\.ipv4\\.conf\\.default\\.send_redirects[\\s]*=[\\s]*0[\\s]*$" "$file"; then echo "PASS"; exit 0; fi
done
echo "FAIL"; exit 1

if ! command -v sysctl &> /dev/null; then echo "PASS"; exit 0; fi
if [ $(sysctl net.ipv4.conf.default.send_redirects | grep -oE '[0-9]+$' | tr -d ' ') -eq 0 ]; then echo "PASS"; exit 0; fi
echo "FAIL"; exit 1

Remediation

Configure the system to not allow interfaces to perform IPv4 ICMP redirects by default. 

Set the system to the required kernel parameter by adding the following line to "/etc/sysctl.conf" or a configuration file in the /etc/sysctl.d/ directory (or modify the line to have the required value):

     net.ipv4.conf.default.send_redirects = 0

Issue the following command to make the changes take effect:

     # sysctl --system