The network element can permit inbound ICMPv6 messages Packet-too-big (type 2), Time Exceeded (type 3), Parameter Problem (type 4), Echo Reply (type 129), and Neighbor Discovery (type 135-136). Remaining ICMPv6 messages must be blocked inbound.

From Perimeter L3 Switch Security Technical Implementation Guide - Cisco

Part of Inbound ICMPv6 messages are not blocked

SV-41069r1_rule The network element can permit inbound ICMPv6 messages Packet-too-big (type 2), Time Exceeded (type 3), Parameter Problem (type 4), Echo Reply (type 129), and Neighbor Discovery (type 135-136). Remaining ICMPv6 messages must be blocked inbound.

Vulnerability discussion

Scanning will usually be the major stage of an information gathering process a malicious computer attacker will launch against a targeted network. With this stage the malicious computer attacker will try to determine what the characteristics of the targeted network are. Techniques, such as host detection, service detection, network topology mapping, and operating system fingerprinting are often used. The data collected will be used to identify those Hosts (if any) that are running a network service, which may have a known vulnerability. This vulnerability may allow the malicious computer attacker to execute a remote exploit in order to gain unauthorized access to those systems. This unauthorized access may become the focal point to the whole targeted network.

Check content

Review the configuration and ensure only approved ICMP types and codes are permitted into the enclave. Use source and destination filtering where appropriate. Apply the ICMP fragment filter to prevent DOS. interface FastEthernet 0/0 description upstream link toward DoD Backbone ipv6 address 2001:db8:60::f14:65a1 ipv6 traffic-filter inbound-to-enclave in ipv6 access-list inbound-to-enclave remark prohibit use of …. remark Specifically block ICMP fragments deny icmp any any fragments log remark Allow inbound ping response to edge router interface permit icmp any 2001:db8:60::f14:65a1 echo-reply remark Allow inbound ping response to public server interface permit icmp any 2001:db8:60::f14:65b1 echo-reply remark Allow Path MTU to function permit icmp any any packet-too-big remark Allow time exceeded messages for loops permit icmp any any time-exceeded remark Allow bad header message to return permit icmp any any parameter-problem remark ND ICMP types generally, but not RD permit icmp any any nd-na permit icmp any any nd-ns remark And explicitly block all other ICMP packets deny ipv6 any any log

Fix text

The network element must be configured to include controls to block inbound exploitable ICMP traffic message types.

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