The Cisco router must be configured to have Internet Control Message Protocol (ICMP) mask reply messages disabled on all external interfaces.
Severity | Group ID | Group Title | Version | Rule ID | Date | STIG Version |
|---|---|---|---|---|---|---|
| medium | V-216566 | SRG-NET-000362-RTR-000114 | CISC-RT-000180 | SV-216566r856185_rule | 2025-08-19 | 3 |
Description
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. Mask Reply ICMP messages are commonly used by attackers for network mapping and diagnosis.
ℹ️ Check
Review the router configuration and verify that ip mask-reply command is not enabled on any external interfaces as shown in the example below.
interface GigabitEthernet0/1
ip address x.x.x.x 255.255.255.0
ip mask-reply
If the ip mask-reply command is configured on any external interface, this is a finding.
✔️ Fix
Disable ip mask-reply on all external interfaces as shown below.
R4(config)#int g0/1
R4(config-if)#no ip mask-reply