RHEL 9 must prevent IPv6 Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257976	RHEL-09-254035	SV-257976r943009_rule		Medium

Description
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.

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

Details

Check Text ( C-61717r943008_chk )

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

Fix Text (F-61641r925914_fix)
Configure RHEL 9 to prevent IPv6 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.ipv6.conf.default.accept_redirects = 0 Load settings from all system configuration files with the following command: $ sudo sysctl --system