The systems local firewall must implement a deny-all, allow-by-exception policy for forwarded packets.
In "iptables" the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to "DROP" implements proper design for a firewall, i.e., any packets which are not explicitly permitted should not be accepted.
Run the following command to ensure the default "FORWARD" policy is "DROP":
# iptables -nvL | grep -i forward
Chain FORWARD (policy DROP 0 packets, 0 bytes)
If the default policy for the FORWARD chain is not set to DROP, this is a finding.
Fix Text (F-19539r377196_fix)
To set the default policy to DROP (instead of ACCEPT) for the built-in FORWARD chain which processes packets that will be forwarded from one interface to another, add or correct the following line in "/etc/sysconfig/iptables":