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-216747	CISC-RT-000180	SV-216747r531087_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 XR Router RTR Security Technical Implementation Guide	2020-09-23

Details

Check Text ( C-17979r288630_chk )
Review the router configuration and verify that ipv4 mask-reply command is not enabled on any external interfaces as shown in the example below. interface GigabitEthernet0/0/0/1 ipv4 address x.11.1.2 255.255.255.252 ipv4 mask-reply If the router configuration has the ipv4 mask-reply command is enabled on any external interfaces, this is a finding.

Fix Text (F-17977r288631_fix)
Disable ipv4 mask-reply on all external interfaces as shown below. RP/0/0/CPU0:R3(config)#int g0/0/0/1 RP/0/0/CPU0:R3(config-if)#no ipv4 mask-reply