The network element can permit outbound ICMPv6 messages Packet-too-big (type 2), Echo Request (type 128), and Neighborhood Discovery (type 135-136). Remaining ICMPv6 messages must be blocked outbound.

From Perimeter Router Security Technical Implementation Guide Cisco

Part of Outbound ICMPv6 traffic is not blocked

SV-15374r2_rule The network element can permit outbound ICMPv6 messages Packet-too-big (type 2), Echo Request (type 128), and Neighborhood Discovery (type 135-136). Remaining ICMPv6 messages must be blocked outbound.

Vulnerability discussion

Scanning will usually be the major stage of an information gathering process a malicious computer attacker will lunch 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 are permitted to exit the enclave. IOS example interface FastEthernet 0/0 description upstream to DoD backbone ipv6 address 2001:db8:60::f14:65a1 ipv6 traffic-filter outbound-from-enclave in ipv6 access-list outbound-from-enclave ….. remark Allow outbound ping request from LAN subnet permit icmp 2001:db8:60::/44 2000::/3 echo-request remark Allow Path MTU to function permit icmp 2001:db8:60::/44 2000::/3 packet-too-big remark Allow ND ICMP types generally, but not RD permit icmp any any nd-na permit icmp any any nd-ns remark Explicitly block all other ICMP packets deny icmp any any log-input remark And explicitly deny by default deny ipv6 any any log-input

Fix text

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

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