The Cisco router must be configured to have Internet Control Message Protocol (ICMP) mask reply messages disabled on all external interfaces.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-216656 | CISC-RT-000180 | SV-216656r855817_rule | Medium |
| 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. |
| STIG | Date |
| Cisco IOS XE Router RTR Security Technical Implementation Guide | 2025-05-16 |
Details
| Check Text (C-17889r287925_chk) |
| 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 Text (F-17887r287926_fix) |
| Disable ip mask-reply on all external interfaces as shown below: R4(config)#int g0/1 R4(config-if)#no ip mask-reply |