OpenBSD 4.3 up to OpenBSD-current: PF null pointer dereference - remote DoS (kernel panic)

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                       Helith - 0815

Author : Rembrandt
Date : 2009-04-09
Affected Software: OpenBSD Kernel
Affected OS : OpenBSD 4.{3,4,5}, OpenBSD-current
Propably older versions are affected as well
Type : Denial of Service

OSVDB :
Milw0rm : 8406
CVE :
ISS X-Force: :
BID : 34482
Secunia : 34676
VUPEN ID :
Trying to fix it responsible and get in contact with the vendor:

– OpenBSD –
Contacted 2009-04-09 15:35 GMT+1
Patch avaiable 2009-04-11 23:43 UTC

We received no response nor a notification about an upcoming patch by
the developers.
– END –

OpenBSDs PF firewall in OpenBSD 4.3 up to OpenBSD-current is prone to a
remote Denial of Service during a null pointer dereference in relation with
special crafted IP datagrams. If the firewall handles such a packet the kernel
panics.

Steps to reproduce:

If you are behind a OpenBSD firewall this nmap scan should trigger the problem
and crash your firewall device:

nmap -sO $some_host_so_that_the_firewall_handles_the_packets

For more informations please do read the patch issued by OpenBSD.

Patches and Workaround:

Patches are provided for OpenBSD 4.3, 4.4, 4.5 (upcoming, release 1st of may)
and OpenBSD-current (via CVS only) and are avaiable at the errata website.
The developers provide hints for a workaround at their errata website too.

Kind regards,
Rembrandt