A vulnerability in some implementations of the IPv6 Neighbor Discovery Protocol may allow a nearby attacker to intercept traffic or cause congested links to become overloaded.
IPv6 networks use the Neighbor Discovery Protocol (NDP) to detect and locate routers and other on-link IPv6 nodes. NDP uses ICMPv6 types 133, 134, 135, and 136. Neighbor solicitation (type 135) messages are used by NDP to discover and determine the reachability of nearby IPv6 nodes. Nodes that can send each other NDP messages are considered to be on-link (as per RFC 4861).
After receiving a neighbor solicitation request from a system that is on-link and is using a spoofed IPv6 address as the source address, a router will create a neighbor cache entry. When this entry is made, some IPv6 implementations will create a Forwarding Information Base (FIB) entry. This FIB entry may cause the router to incorrectly forward traffic to the device that sent original spoofed neighbor solicitation request.
An attacker may be able to intercept private network traffic. Receiving the traffic may cause links to become congested or saturated due to the additional bandwidth. Administrators are encouraged to read RFC 3756 for more information about other possible vulnerabilities and impacts.
Consider the workarounds below and consult your vendor.
Block packets with illogical source addresses
Thanks to David Miles for reporting this vulnerability. Numerous vendors and others also provided technical information that was used in this report.