FreeBSD -- ICMPv6 / MLDv2 out-of-bounds memory access

Problem Description:

The ICMPv6 input path incorrectly handles cases where an MLDv2 listener query packet is internally fragmented across multiple mbufs.

Impact:

A remote attacker may be able to cause an out-of-bounds read or write that may cause the kernel to attempt to access an unmapped page and subsequently panic.