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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230535	RHEL-08-040210	SV-230535r627750_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	2021-03-04

Details

Check Text ( C-33204r568351_chk )

Verify RHEL 8 will not accept ICMP redirect messages. Note: If either IPv4 or IPv6 is disabled on the system, this requirement only applies to the active internet protocol version. Check the value of the default "accept_redirects" variables with the following command: $ sudo sysctl net.ipv4.conf.default.accept_redirects net.ipv6.conf.default.accept_redirects net.ipv4.conf.default.accept_redirects = 0 net.ipv6.conf.default.accept_redirects = 0 If the returned lines do not have a value of "0", or a line is not returned, this is a finding.

Fix Text (F-33179r568352_fix)

Configure RHEL 8 to prevent ICMP redirect messages from being accepted with the following command: $ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0 $ sudo sysctl -w net.ipv6.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 net.ipv6.conf.default.accept_redirects=0