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Category:   OS (UNIX)  >   NetBSD Vendors:   NetBSD
NetBSD elf_load_file() Validation Error Lets Local Users Crash the System
SecurityTracker Alert ID:  1015848
SecurityTracker URL:  http://securitytracker.com/id/1015848
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Mar 30 2006
Impact:   Denial of service via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 2.0, 2.1, 3.0
Description:   A vulnerability was reported in NetBSD. A local user can cause denial of service conditions.

The elf_load_file() function does not properly handle interpreters without a PT_LOAD section defined in the header. A malformed ELF interpreter can trigger a NULL pointer deference in the kernel.

The NetBSD 2.x branches are only affected if the kernel is compiled with the USE_TOPDOWN_VM option (not the default in GENERIC kernels).

Eric Haszlakiewicz reported this vulnerability.

Impact:   A local user can cause the system to crash.
Solution:   NetBSD has issued a fix.

The NetBSD advisory is available at:

ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-008.txt.asc

Vendor URL:  www.netbsd.org/ (Links to External Site)
Cause:   Input validation error

Message History:   None.


 Source Message Contents

Subject:  NetBSD Security Advisory 2006-008: Malformed ELF interpreter causes


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		 NetBSD Security Advisory 2006-008
		 =================================

Topic:		Malformed ELF interpreter causes system crash

Version:	NetBSD-current:	source prior to March 17, 2006
		NetBSD 3.0:	affected
		NetBSD 2.1:	affected
		NetBSD 2.0.*:	affected
		NetBSD 2.0:	affected

Severity:	Any local user can crash the system

Fixed:		NetBSD-current:		March 17, 2006
		NetBSD-3-0 branch:	March 20, 2006
						(3.0.1 will include the fix)
		NetBSD-3   branch:	March 20, 2006
		NetBSD-2-1 branch:	March 20, 2006
						(2.1.1 will include the fix)
		NetBSD-2-0 branch:	March 20, 2006
						(2.0.4 will include the fix)
		NetBSD-2   branch:	March 20, 2006

Abstract
========

A malformed copy of ld.elf_so, or any other elf interpreter, can cause
a NULL pointer deference in the kernel.

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

The elf_load_file() function assumed that an interpreter always has a
PT_LOAD section defined in it's header.  That is not necessarily the
case, as an attacker can trivially create an interpreter that
does not have that, and a binary that uses that interpreter.

The netbsd-2, netbsd-2-0 and netbsd-2-1 branches are only vulnerable
if the kernel is compiled with the USE_TOPDOWN_VM option which is
not set by default in GENERIC kernels.

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

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

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 sys/kern/exec_elf32.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
=========

Eric Haszlakiewicz for PoC code and implementing the fixes.
Coverity for access to the scans of the NetBSD source code.

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

	2006-03-29	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 
  ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-008.txt.asc

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


Copyright 2006, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-008.txt,v 1.5 2006/03/29 11:14:28 adrianp Exp $

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