Vulnerability Discussion
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.
Check
Verify RHEL 8 ignores IPv4 ICMP redirect messages.
Note: If IPv4 is disabled on the system, this requirement is Not Applicable.
Check the value of the "accept_redirects" variables with the following command:
$ sudo sysctl net.ipv4.conf.all.accept_redirects
net.ipv4.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.
Fix
Configure RHEL 8 to ignore IPv4 ICMP redirect messages with the following command:
$ sudo sysctl -w net.ipv4.conf.all.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.all.accept_redirects = 0