V-217022

Discussion

The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Host unreachable ICMP messages are commonly used by attackers for network mapping and diagnosis.

Check Content

Review the firewall hierarchy configuration to verify that all packets that are not permitted are silently dropped using the discard parameter as shown in the configuration example below.

firewall {
    family inet {
        …
        …
        …
        }
        filter FILTER_INBOUND {
            term ALLOW_XYZ {
                from {
                    protocol xyz;
                }
                then accept;
            }
            …
            …
            …
            }
            term DENY_BY_DEFAULT {
                then {
                    log;
                    discard;
                }
            }
        }
    }

If ICMP unreachable notifications are sent for packets that are dropped, this is a finding.