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Category:   Application (Generic)  >   Xlock Vendors:   IBM
Xlock Buffer Overflow Lets Local Users Gain Root Privileges
SecurityTracker Alert ID:  1016923
SecurityTracker URL:  http://securitytracker.com/id/1016923
CVE Reference:   CVE-2006-5009   (Links to External Site)
Updated:  Jun 3 2008
Original Entry Date:  Sep 26 2006
Impact:   Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in Xlock. A local user can obtain root privileges on the target system.

A local user can trigger a buffer overflow to execute arbitrary code on the target system with root privileges.

A remote authenticated user may also be able to exploit this flaw.

The 'X11.apps.clients' fileset is affected.

Impact:   A local user can obtain root privileges on the target system.
Solution:   IBM has issued the following fixes:

APAR number for AIX 5.2.0: IY87943 (available)
APAR number for AIX 5.3.0: IY87894 (available approx. 10/04/06)

Interim fixes are available at:

ftp://aix.software.ibm.com/aix/efixes/security/xlock_ifix.tar.Z

Vendor URL:  www.ibm.com/ (Links to External Site)
Cause:   Boundary error
Underlying OS:   UNIX (AIX)

Message History:   None.


 Source Message Contents

Date:  Mon, 25 Sep 2006 20:58:15 -0400
Subject:  IBM AIX xlock vulnerability


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

IBM SECURITY ADVISORY


First Issued: Mon Sep 25 10:00 CDT 2006
==========================================================================
                           VULNERABILITY SUMMARY

VULNERABILITY:      A vulnerability in the xlock command may allow a user
                    to execute arbitrary code with root privileges.

PLATFORMS:          AIX 5.2 and 5.3.

SOLUTION:           Apply the APAR, interim fix or workaround as 
		    described below.

THREAT:             A local user may execute arbitrary code with root
                    privileges.

CERT VU Number:     n/a
CVE Number:         n/a
==========================================================================
                           DETAILED INFORMATION


I.  Description
===============

A buffer overflow vulnerability in the xlock command may allow a local user
to execute arbitrary code with root privileges. xlock is used to lock the
local X display until a password is entered. It may be possible for a user
that connects to the X server remotely to exploit this issue.

xlock ships as part of the X11.apps.clients fileset. To determine if this
fileset is installed, execute the following command:

# lslpp -L X11.apps.clients 

If the fileset is installed it will be listed along with its version
information, state, type and a description.

The following table shows the vulnerable versions of X11.apps.clients.

AIX Release          Lower         Upper
                     Level         Level
===========================================
AIX 5.2              5.2.0.0       5.2.0.0
AIX 5.3              5.3.0.0       5.3.0.30


II. Impact
==========

A user may execute arbitrary code as the root user.


III.  Solutions
===============

A. APARs

IBM provides the following fixes:

      APAR number for AIX 5.2.0:  IY87943 (available)
      APAR number for AIX 5.3.0:  IY87894 (available approx. 10/04/06)

NOTE: Affected customers are urged to upgrade to the latest applicable
Technology Level.

B. Interim Fix

Interim fixes are available. The interim fixes can be downloaded via ftp
from:

    ftp://aix.software.ibm.com/aix/efixes/security/xlock_ifix.tar.Z

This is a compressed tarball containing this advisory, interim fix packages
and cleartext PGP signatures for each package.


Verify you have retrieved the fixes intact:
+------------------------------------------
The interim fixes below are named by using the APAR corresponding to the
release that the fix applies to. The APAR is followed by an underscore and
the Technology Level for the particular AIX release that a fix applies to.

The checksums below were generated using the "sum" and "md5sum" commands
and are as follows:

The interim fixes below include prerequisite checking. This will enforce
the correct mapping between the fixes and AIX Technology Levels.

Filename                   sum           md5
=========================================================================
IY87894_03.060907.epkg.Z   21748    46   5a26f80801c4b4518378a1443b9351a6
IY87894_04.060907.epkg.Z   00324    46   def13086926f028cf77a653bcfb8731c
IY87894_05.060907.epkg.Z   52816    46   6d2b0c17bc15e86373dcffcbb6a4e3c1
IY87943_07.060907.epkg.Z   21187    45   1239bb9dc9d5615cdad271c16062f7de
IY87943_08.060907.epkg.Z   10713    45   e9d8136a0a5b35ca16d53b32a7286673
IY87943_09.060907.epkg.Z   43155    45   0649075bfe5ce0cb24f2660716ec925b


These sums should match exactly. The PGP signatures in the compressed
tarball and on this advisory can also be used to verify the integrity of
the various files they correspond to. If the sums or signatures cannot be
confirmed, double check the command results and the download site address.
If those are OK, contact IBM AIX Security at security-alert@austin.ibm.com
and describe the discrepancy.

The interim fixes include prerequisite checking. This will ensure the
correct mapping between the interim fixes and AIX Technology Levels. The
following table shows the prerequisite fileset levels required for the
fixes above. The fileset levels listed are for X11.apps.clients.

Interim                    Fileset Level     Fileset Level
Fix                        (lower limit)     (upper limit)
===================================================================
IY87943_07.060907.epkg.Z   5.2.0.0           5.2.0.0
IY87943_08.060907.epkg.Z   5.2.0.0           5.2.0.0
IY87943_09.060907.epkg.Z   5.2.0.0           5.2.0.0
IY87894_03.060907.epkg.Z   5.3.0.30          5.3.0.30
IY87894_04.060907.epkg.Z   5.3.0.30          5.3.0.30
IY87894_05.060907.epkg.Z   5.3.0.30          5.3.0.30


IMPORTANT: If possible, it is recommended that a mksysb backup of the
system is created. Verify it is both bootable, and readable before
proceeding.

Customers may contact IBM support if any issues arise with these interim
fixes.


Interim Installation Instructions:
+---------------------------------

These packages use the new Interim Fix Management Solution to install and
manage interim fixes. More information can be found at:

     http://www14.software.ibm.com/webapp/set2/sas/f/aix.efixmgmt/home.html

To preview an epkg interim fix installation execute the following command:

# emgr -e ipkg_name -p       # where ipkg_name is the name of the
                             # interim fix package being previewed.

To install an epkg interim fix package, execute the following command:

# emgr -e ipkg_name -X       # where ipkg_name is the name of the
                             # interim fix package being installed.

The "X" flag will expand any filesystems if required.

C. Workaround

Remove the setuid root bit. Note that this will prevent xlock from
functioning normally. This can be done by executing the following command:

# chmod 755 /usr/lpp/X11/bin/xlock

Verify the changes:

# ls -la /usr/lpp/X11/bin/xlock   
- -rwxr-xr-x   1 root     system      36273 Sep  7 11:55 /usr/lpp/X11/bin/xlock


IV. Obtaining Fixes
===================

AIX Version 5 APARs can be downloaded from:

     http://www.ibm.com/servers/eserver/support/unixservers/aixfixes.html

Security related Interim Fixes can be downloaded from:

     ftp://aix.software.ibm.com/aix/efixes/security


V.  Contact Information
=======================

If you would like to receive AIX Security Advisories via email, please
visit:

     http://www14.software.ibm.com/webapp/set2/subscriptions/pqvcmjd

Comments regarding the content of this announcement can be directed to:

     security-alert@austin.ibm.com

To request the PGP public key that can be used to communicate securely
with the AIX Security Team send email to security-alert@austin.ibm.com
with a subject of "get key". The key can also be downloaded from a PGP
Public Key Server. The key id is 0x1B14F299.

Please contact your local IBM AIX support center for any assistance.

eServer is a trademark of International Business Machines Corporation.
IBM, AIX and pSeries are registered trademarks of International Business
Machines Corporation. All other trademarks are property of their respective
holders.
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