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 | CCI-002385 | 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-216656r855817_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