FreeBSD -- Remote kernel panics on IPv6 connections

Problem Description:
In case of an incoming ICMPv6 ‘Packet Too Big Message’, there
is an insufficient check on the proposed new MTU for a path to
the destination.
Impact:
When the kernel is configured to process IPv6 packets and has
active IPv6 TCP sockets, a specifically crafted ICMPv6 ‘Packet
Too Big Message’ could cause the TCP stack of the kernel to
panic.
Workaround:
Systems without INET6 / IPv6 support are not vulnerable and
neither are systems which do not listen on any IPv6 TCP sockets
and have no active IPv6 connections.
Filter ICMPv6 ‘Packet Too Big Messages’ using a firewall, but
this will at the same time break PMTU support for IPv6
connections.