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

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.

Note: If IPv6 is disabled on the system, this requirement is Not Applicable.

Verify that OL 9 will not accept IPv6 ICMP redirect messages.

Check the value of the default "accept_redirects" variables with the following command:

$ 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.

Configure OL 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