The Photon operating system must prevent IPv4 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.

At the command line, run the following command to verify ICMP redirects are not accepted:

# /sbin/sysctl -a --pattern "net.ipv4.conf.(all|default).accept_redirects"

Expected result:

net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0

If the "accept_redirects" kernel parameters are not set to "0", this is a finding.

Navigate to and open:

/etc/sysctl.d/zz-stig-hardening.conf

Add or update the following lines:

net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0

At the command line, run the following command to load the new configuration:

# /sbin/sysctl --load /etc/sysctl.d/zz-stig-hardening.conf

Note: If the file zz-stig-hardening.conf does not exist, it must be created.