RHEL 8 must prevent IPv4 Internet Control Message Protocol (ICMP) redirect messages from being accepted.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-244550	RHEL-08-040209	SV-244550r743899_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 8 Security Technical Implementation Guide	2021-06-14

Details

Check Text ( C-47825r743897_chk )

Verify RHEL 8 will not accept IPv4 ICMP redirect messages. Note: If IPv4 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.ipv4.conf.default.accept_redirects net.ipv4.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.

Fix Text (F-47782r743898_fix)
Configure RHEL 8 to prevent IPv4 ICMP redirect messages from being accepted with the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0 If "0" is not the system's default value then add or update the following line in the appropriate file under "/etc/sysctl.d": net.ipv4.conf.default.accept_redirects=0