NetBSD Security Advisory 2010-013: UDP6 Option Parsing local Denial of Service

[NetBSD Security Officer <security-officer%NetBSD.org@localhost>]

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                 NetBSD Security Advisory 2010-013
                 =================================

Topic:          UDP6 Option Parsing local Denial of Service

Version:        NetBSD-current:         affected prior to Jul 15, 2010
                NetBSD 5.1:             not affected
                NetBSD 5.0.*:           affected
                NetBSD 5.0:             affected
                NetBSD 4.0.*:           affected
                NetBSD 4.0:             affected

Severity:       Local system crash

Fixed:          NetBSD-current:         Jul 15, 2010
                NetBSD-5-0 branch:      Jul 16, 2010
                NetBSD-5 branch:        Jul 16, 2010 (5.1 includes the fix)
                NetBSD-4-0 branch:      Jul 16, 2010
                NetBSD-4 branch:        Jul 16, 2010

Please note that NetBSD releases prior to 4.0 are no longer supported.
It is recommended that all users upgrade to a supported release.


Abstract
========

The udp6_output() routing did not do proper variable management
allowing an attacker to crash a local system by sending an UDP6
datagram with suitable parameters.


Technical Details
=================

The udp6_output() can be given ancilliary data in the "control"
parameter.  This is used to create the IPv6 packet options in the
"opt" variable.  The packet options are released at the end of the
routine after the packet has been sent.  However, when given other
bad parameters, the routine would jump to releasing the options
without ever creating them first.  This leads to an uninitialized
pointer access.


Solutions and Workarounds
=========================

The following instructions describe how to upgrade your kernel by
updating your source tree and rebuilding and installing a new
version of the kernel.

Only kernels compiled with the following option are vulnerable to this issue:

        options INET6

The default NetBSD GENERIC kernels have this option enabled.

If you do not use IPv6 access, as a temporary workaround, filter all IPv6
UDP traffic from untrusted networks (mind that UDP sender is very easy to
forge) until the system can receive a fixed kernel.

For all NetBSD versions, you need to obtain fixed kernel sources,
rebuild and install the new kernel, and reboot the system.

  CVS branch    file                                    revision
  ------------- --------------------------              -----------
  HEAD          sys/netinet6/udp6_output.c              1.41
  netbsd-5      sys/netinet6/udp6_output.c              1.37.4.1
  netbsd-5-0    sys/netinet6/udp6_output.c              1.37.10.1
  netbsd-4      sys/netinet6/udp6_output.c              1.26.8.1
  netbsd-4-0    sys/netinet6/udp6_output.c              1.26.14.1

The fixed source may be obtained from the NetBSD CVS repository.        

The following instructions briefly summarise how to upgrade your        
kernel.  In these instructions, replace:

  ARCH     with your architecture (from uname -m), and                  
  KERNCONF with the name of your kernel configuration file.    

To update from CVS, re-build, and re-install the kernel:

        # cd src
        # cvs update -d -P -r BRANCH sys/netinet6/upd6_output.c
        # ./build.sh kernel=KERNCONF
        # mv /netbsd /netbsd.old
        # cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd 
        # shutdown -r now

For more information on how to do this, see:    

   http://www.NetBSD.org/guide/en/chap-kernel.html

Thanks To
=========

We thank Clement LECIGNE for reporting the issue and providing a
suggested fix.

Revision History
================

        2010-11-29      Initial release

More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at 
  http://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2010-013.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/ .

Copyright 2010, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2010-013.txt,v 1.2 2010/11/28 15:16:17 tonnerre Exp $

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