*no comment* writes "If you are running OpenBSD on your IPv6 install, it might be time to upgrade to -current. (just kidding) There is, however, a way to crash OpenBSD 3.4 with a couple of simple IPv6 commands. Georgi Guninski, found the problem. To quote Theo, 'it is just a crash.'"
It is unknown if the bug could be used to execute arbitrary code, but it does require patching a Linux kernel (or rolling your own network stack) to exploit.