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CERT Advisory 145
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CERT* Advisory CA-97.13
Original issue date: May 7, 1997
Last revised: June 4, 1997
Appendix A - updated vendor information for BSDI.
A complete revision history is at the end of this file.
Topic: Vulnerability in xlock
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The CERT Coordination Center has received reports that a buffer overflow
condition exists in some implementations of xlock. This vulnerability makes it
possible for local users (users with access to an account on the system) to
execute arbitrary programs as a privileged user.
Exploitation information involving this vulnerability has been made publicly
available.
If your system is vulnerable, the CERT/CC team recommends installing a
patch from your vendor. If you are not certain whether your system is
vulnerable or if you know that your system is vulnerable and you cannot add a
patch immediately, we urge you to apply the workaround described in
Section III.B.
We will update this advisory as we receive additional information.
Please check our advisory files regularly for updates that relate to your site.
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I. Description
xlock is a program that allows a user to "lock" an X terminal. A buffer
overflow condition exists in some implementations of xlock. It is
possible attain unauthorized access to a system by engineering a
particular environment and calling a vulnerable version of xlock that has
setuid or setgid bits set. Information about vulnerable versions must be
obtained from vendors. Some vendor information can be found in Appendix A
of this advisory.
Exploitation information involving this vulnerability has been made
publicly available.
Note that this problem is different from that discussed in CERT Advisory
CA-97.11.libXt.
II. Impact
Local users are able to execute arbitrary programs as a privileged user
without authorization.
III. Solution
Install a patch from your vendor as described in Solution A. If you are
not certain whether your system is vulnerable or if you know that your
system is vulnerable and you cannot install a patch immediately, we
recommend Solution B.
A. Obtain and install a patch for this problem.
Below is a list of vendors who have provided information about
xlock. Details are in Appendix A of this advisory; we will
update the appendix as we receive more information. If your
vendor's name is not on this list, the CERT/CC did not hear from
that vendor. Please contact your vendor directly.
Berkeley Software Design, Inc. (BSDI)
Cray Research - A Silicon Graphics Company
Data General Corporation
Digital Equipment Corporation
FreeBSD, Inc.
Hewlett-Packard Company
IBM Corporation
LINUX
NEC Corporation
The Open Group [This group distributes the publicly available software
that was formerly distributed by X Consortium]
Solbourne
Sun Microsystems, Inc.
B. We recommend the following workaround if you are not certain
whether your system is vulnerable or if you know that your system
is vulnerable and you cannot install a patch immediately.
1. Find and disable any copies of xlock that exist on your system and
that have the setuid or setgid bits set.
2. Install a version of xlock known to be immune to this
vulnerablility. One such supported tool is xlockmore. The latest
version of this tool is 4.02, and you should ensure that this is
the version you are using. This utility can be obtained from the
following site:
ftp://ftp.x.org/contrib/applications/xlockmore-4.02.tar.gz
MD5 (xlockmore-4.02.tar.gz) = c158e6b4b99b3cff4b52b39219dbfe0e
You can also obtain this version from mirror sites. A list of
these sites will be displayed if you are not able to access the
above archive due to load.
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Appendix A - Vendor Information
Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, the CERT/CC did not hear from that
vendor. Please contact the vendor directly.
Berkeley Software Design, Inc. (BSDI)
=====================================
BSD/OS 2.1 is vulnerable to the xlock vulnerability. BSDI recommends that 2.1
customers either upgrade to BSD/OS 3.0 or remove the setuid permission from
/usr/X11/bin/xlock.
Cray Research - A Silicon Graphics Company
==========================================
Cray Research does not include xlock in its X Window releases, so we are
not at risk on the xlock buffer overflow problem.
Data General Corporation
========================
The xlock sources (xlockmore-3.7) that DG includes in its contributed
software package have been modified to remove this vulnerability. These
will be available when release 8 comes out. We also recommend that our
customers who have the current version should change the sprintf calls in
resource.c to snprintf calls, rebuild and reinstall the package.
Digital Equipment Corporation
=============================
This reported problem is not present for Digital's ULTRIX or
Digital UNIX Operating Systems Software.
FreeBSD, Inc.
=============
The xlockmore version we ship in our ports collection is vulnerable
in all shipped releases. The port in FreeBSD-current is fixed.
Solution is to install the latest xlockmore version (4.02).
Hewlett-Packard Company
=======================
We ship an suid root program vuelock that is based on xlock.
It does have the vulnerability.
The only workaround is to remove the executable, the patch is "in process".
IBM Corporation
===============
AIX is vulnerable to the conditions described in this advisory.
The following APARs will be released soon:
AIX 3.2: APAR IX68189
AIX 4.1: APAR IX68190
AIX 4.2: APAR IX68191
IBM and AIX are registered trademarks of International Business Machines
Corporation.
LINUX
=====
Red Hat:
Not vulnerable
Caldera:
Not vulnerable
Debian:
An updated package is on the Debian site
SuSE:
ftp://ftp.suse.com/pub/SuSE-Linux/suse_update/S.u.S.E.-4.4.1/xap1/xlock
And in general the new Xlockmore release fixes the problems.
NEC Corporation
===============
UX/4800 Not vulnerable for all versions.
EWS-UX/V(Rel4.2MP) Not vulnerable for all versions.
EWS-UX/V(Rel4.2) Not vulnerable for all versions.
UP-UX/V(Rel4.2MP) Not vulnerable for all versions.
The Open Group
==============
Publicly available software that was formerly distributed by the X Consortium -
Not vulnerable.
Solbourne
=========
Solbourne is not vulnerable to this attack.
Sun Microsystems, Inc.
======================
We are producing patches for OpenWindows 3.0 for Sun OS versions
4.1.3_U1, 4.1.4, 5.3, 5.4, 5.5, and 5.5.1.
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The CERT Coordination Center thanks David Hedley for reporting the original
problem and Kaleb Keithley at The Open Group for his support in the
development of this advisory.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident Response
and Security Teams (see http://www.first.org/team-info/).
CERT/CC Contact Information
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Email cert@cert.org
Phone +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30-5:00 p.m. EST(GMT-5) / EDT(GMT-4)
and are on call for emergencies during other hours.
Fax +1 412-268-6989
Postal address
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
USA
Using encryption
We strongly urge you to encrypt sensitive information sent by email. We can
support a shared DES key or PGP. Contact the CERT/CC for more information.
Location of CERT PGP key
ftp://info.cert.org/pub/CERT_PGP.key
Getting security information
CERT publications and other security information are available from
http://www.cert.org/
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
comp.security.announce
To be added to our mailing list for advisories and bulletins, send
email to
cert-advisory-request@cert.org
In the subject line, type
SUBSCRIBE your-email-address
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* Registered U.S. Patent and Trademark Office.
Copyright 1997 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.
The CERT Coordination Center is part of the Software Engineering Institute
(SEI). The SEI is sponsored by the U.S. Department of Defense.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.13.xlock
http://www.cert.org
click on "CERT Advisories"
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Revision history
June 4, 1997 Appendix A - updated vendor information for BSDI.
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