Packet Filter Null Pointer Dereference

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Helith - 0815  
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Author : Rembrandt  
Date : 2009-04-30  
Found : 2009-04-09  
Affected Software: PF (OpenBSD Packet Filter)  
Affected OS : OpenBSD 4.2 up to 4.5 and HEAD branch up to 2009-04-11  
NetBSD 5.x up to RC3 and HEAD branch up to 2009-04-13  
MirOS #10 and earlier  
MidnightBSD 0.3-current  
Not affected OS : FreeBSD  
NetBSD 3.x, 4.x, 5.x (patched before release)  
DragonflyBSD  
Debian GNU/kFreeBSD  
MidnightBSD prior 0.3  
  
Older versions of OpenBSD PF and products based  
thereon might be affected as well.  
The Bug was introduced between the OpenBSD 4.1 and 4.2  
release.  
  
Type : Denial of Service  
  
OSVDB : 53608  
Milw0rm : 8406  
CVE :   
ISS X-Force: :   
BID : 34482  
Secunia : 34676   
VUPEN ID : ADV-2009-1015  
  
This advisory supercedes the original advisory which was just related to  
OpenBSD because we had to publish an announcement in response to OpenBSD's  
reaction.  
  
Trying to fix it responsibly and get in contact with the vendor:  
  
-- OpenBSD --  
Contacted 2009-04-09 16:35 UTC  
Patch available 2009-04-11 23:43 UTC  
  
We received no response nor a notification about an upcoming patch.  
Also we had no chance to coordinate or inform other projects before OpenBSD  
issued the patch and a statement.  
  
We like to mention that the issued patch is just a workaround and does not  
patch or remove the affected code.  
  
-- NetBSD --  
Contacted and asked for confirmation 2009-04-15 06:00 UTC  
Were informed about further investigations 2009-04-15 9:42 UTC  
Received information about upcoming Patches 2009-04-15 11:57 UTC  
Received confirmation for 5.x up to RC3 and HEAD 2009-04-15 12:17 UTC  
  
We thank the NetBSD team that they patched the PF bug prior the 5.x release!  
  
-- FreeBSD --  
Contacted and asked for confirmation 2009-04-15 06:56 UTC  
Were informed about further investigations 2009-04-15 7:56 UTC  
Were informed about not being vulnerable 2009-04-15 22:05 UTC  
  
-- DragonflyBSD --  
Contacted and asked for confirmation 2009-04-15 06:10 UTC  
Were informed about not being vulnerable 2009-04-15 21:35 UTC  
  
-- MirOS (MirBSD) --  
Contacted and asked for official confirmation 2009-04-15 06:36 UTC  
Received confirmation for MirBSD 10 and prior 2009-04-15 17:57 UTC  
  
-- MidnightBSD --  
Contacted and asked for official confirmation 2009-04-15 20:17 UTC  
Received confirmation for MidnightBSD 2009-04-15 22:37 UTC  
  
-- Debian GNU/kFreeBSD --  
Contacted and asked for official confirmation 2009-04-15 22:41 UTC  
Were informed about not being vulnerable 2009-04-15 23:35 UTC  
-- END --  
  
  
OpenBSDs PF firewall is prone to a remote Denial of Service due to a NULL-  
pointer dereference when handling special crafted IP datagrams. If the  
firewall handles such a packet the kernel panics.  
An example for such a packet would be a IPv4 packet with a ICMPv6 payload.  
  
This affects multiple vendors because PF was incorporated into serveral OS.  
  
The problem stems from the unification of the rule processing in pf_test_rule().  
With this unification ICMPv6 logic was applied to IPv4 packets and vice versa.  
Because the handling logic asserts that the common code in pf_test has verified  
that the packet contains a full ICMP header and has pulled up the mbuf up to  
that point. This assertion fails when the wrong AF-version is used by pf_test  
and thus pf_test_rule tries to access not allocated memory.  
The affected function is in pf_change_a6 and the patch is just a workaround  
because it filters the packet in pf_test() except of fixing the affected source  
code.  
  
  
Steps to reproduce:  
  
If you have an affected OS in your network which does NAT or redirecting traffic  
you should be able to test your IPv4 device with this simple hping command:  
  
hping -0 -H 58 $a_host  
  
  
Patches are provided for:  
  
OpenBSD 4.3 - 4.5 (not for 4.2), HEAD after 2009-04-11  
NetBSD 4.x (patched for consistency) - 5.0RC3, HEAD after 2009-04-13  
MirBSD 10  
MidnightBSD 0.3-current  
  
  
Workaround:  
  
The OpenBSD developers provide hints for a workaround at their errata  
website too.  
  
  
We like to thank the security teams of the following projects for  
their friendly cooperation:  
  
DragonflyBSD  
NetBSD  
FreeBSD  
MidnightBSD   
MirBSD  
  
Special thanks goes to Andreas Bogk who assisted in the assembly analysis and  
Adrian Portelli of the NetBSD project for his time and permanent suggestions.  
  
  
Kind regards,  
Rembrandt  
  
  
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