bugtraq - OpenBSD 4.3 up to OpenBSD-current: PF null pointer dereference

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Date: Mon, 13 Apr 2009 19:39:15 +0200
From: rembrandt <rembrandt@...ith.net>
To: bugtraq@...urityfocus.com
Subject: 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