RHEL 9 must not forward IPv4 source-routed packets by default.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257964	RHEL-09-253045	SV-257964r991589_rule		Medium

Description
Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It must be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router.

Description

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It must be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2024-06-04

Details

Check Text ( C-61705r942992_chk )
Verify RHEL 9 does not accept IPv4 source-routed packets by default. Check the value of the accept source route variable with the following command: $ sudo sysctl net.ipv4.conf.default.accept_source_route net.ipv4.conf.default.accept_source_route = 0 If the returned line does not have a value of "0", a line is not returned, or the line is commented out, this is a finding. Check that the configuration files are present to enable this network parameter. $ sudo /usr/lib/systemd/systemd-sysctl --cat-config \| egrep -v '^(#\|;)' \| grep -F net.ipv4.conf.default.accept_source_route \| tail -1 net.ipv4.conf.default.accept_source_route = 0 If "net.ipv4.conf.default.accept_source_route" is not set to "0" or is missing, this is a finding.

Check Text ( C-61705r942992_chk )

Verify RHEL 9 does not accept IPv4 source-routed packets by default.

Check the value of the accept source route variable with the following command:

$ sudo sysctl net.ipv4.conf.default.accept_source_route

net.ipv4.conf.default.accept_source_route = 0

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

Check that the configuration files are present to enable this network parameter.

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F net.ipv4.conf.default.accept_source_route | tail -1

net.ipv4.conf.default.accept_source_route = 0

If "net.ipv4.conf.default.accept_source_route" is not set to "0" or is missing, this is a finding.

Fix Text (F-61629r925878_fix)
Configure RHEL 9 to not forward IPv4 source-routed packets by default. Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory: net.ipv4.conf.default.accept_source_route = 0 Load settings from all system configuration files with the following command: $ sudo sysctl --system