PuffyThe OpenBSD has just released patch 010 for OpenBSD 4.0.

This is a security fix and applies to all architectures.

Quote from the Errata page:

Incorrect mbuf handling for ICMP6 packets.
Using pf(4) to avoid the problem packets is an effective workaround until the patch can be installed.
Use "block in inet6" in /etc/pf.conf.

As always, I’ve created a binpatch for OpenBSD 4.0.