RHEL 9 must ignore IPv6 Internet Control Message Protocol (ICMP) redirect messages.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257972	RHEL-09-254015	SV-257972r925903_rule		Medium

Description
An illicit ICMP redirect message could result in a man-in-the-middle attack.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61713r925901_chk )

Verify RHEL 9 ignores IPv6 ICMP redirect messages. Note: If IPv6 is disabled on the system, this requirement is Not Applicable. Check the value of the "accept_redirects" variables with the following command: $ sysctl net.ipv6.conf.all.accept_redirects net.ipv6.conf.all.accept_redirects = 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.ipv6.conf.all.accept_redirects | tail -1 net.ipv6.conf.all.accept_redirects = 0 If "net.ipv6.conf.all.accept_redirects" is not set to "0" or is missing, this is a finding.

Fix Text (F-61637r925902_fix)
Configure RHEL 9 to ignore IPv6 ICMP redirect messages. Add or edit the following line in a single system configuration file, in the "/etc/sysctl.d/" directory: net.ipv6.conf.all.accept_redirects = 0 Load settings from all system configuration files with the following command: $ sudo sysctl --system