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CERT Advisory 143
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=============================================================================
CERT* Advisory CA-97.11
Original issue date: May 1, 1997
Last revised: -- May 8, 1997
Appendix A - updated vendor information for Hewlett-Packard.
A complete revision history is at the end of this file.
Topic: Vulnerability in libXt
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There have been discussions on public mailing lists about buffer overflows in
the Xt library of the X Windowing System made freely available by The Open
Group (and previously by the now-defunct X Consortium). The specific problem
outlined in those discussions was a buffer overflow condition in the Xt
library, and the file xc/lib/Xt/Error.c. Exploitation scripts were made
available.
Since then (the latter half of 1996), The Open Group has extensively reviewed
the source code for the entire distribution to address the potential for
further buffer overflow conditions. These conditions can make it possible for
a local user to execute arbitrary instructions as a privileged user without
authorization.
The programs that pose a potential threat to sites are those programs that
have been built from source code prior to X11 Release 6.3 and have setuid or
setgid bits set. Some third-party vendors distribute derivatives of the X
Window System, and if you use a distribution that includes X tools that have
setuid or setgid bits set, you may be vulnerable as well.
The CERT/CC team recommends upgrading to X11 Release 6.3 or installing a
patch from your vendor. If you cannot do one of these, then as a last resort
we recommend that you remove the setuid or setgid bits from any executable
files contained in your distribution of X; this may have an adverse effect on
some system operations.
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
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I. Description
There have been discussions on public mailing lists about buffer
overflows in the Xt library of the X Windowing System made freely
available by The Open Group (and previously by the now-defunct X
Consortium). During these discussions, exploitation scripts were made
available for some platforms.**
The specific problem outlined in those discussions was a buffer overflow
condition in the Xt library and the file xc/lib/Xt/Error.c. It was
possible for a user to execute arbitrary instructions as a privileged
user using a program built by this distribution with setuid or setgid
bits set.
Note that in this case a root compromise was only possible when
programs built from this distribution (e.g., xterm) were setuid
root.
Since then The Open Group has extensively reviewed the source code for
the entire distribution to address the potential for further buffer
overflow condition.
If you use a distribution of the X Windowing System earlier than
X11 Release 6.3 that you downloaded and compiled yourself, we
encourage you to take the steps outlined in either Section IV A or C.
If you use third-party vendor-supplied distributions of the X
Windowing System containing setuid root programs, we encourage
you to take the steps outlined in Sections IV B or C.
** Note: Discussions of this specific instance of the vulnerability
appeared on mailing lists during the second half of 1996. Exploitation
scripts were made public at that time.
II. Impact
Platforms that have X applications built with the setuid or setgid bits
set may be vulnerable to buffer overflow conditions. These conditions can
make it possible for a local user to execute arbitrary instructions as a
privileged user without authorization. Access to an account on the system
is necessary for exploitation.
III. Finding Potentially Vulnerable Distributions
A. For Sites That Download and Build Their Own Distributions
As discussed earlier, the programs that pose a potential threat to sites
are those programs that have been built from source code, prior to X11
Release 6.3 and have setuid or setgid bits set.
Sites that have downloaded the X source code from the X Consortium
should be able to identify such programs by looking in the directory
hierarchy defined by the "ProjectRoot" constant described in the
xc/config/cf/site.def file in the source code distribution. The
default is /usr/X11R6.3. The X11R6.3 Installation Guide states:
"ProjectRoot
The destination where X will be installed. This variable
needs to be set before you build, as some programs that read
files at run-time have the installation directory compiled
in to them. Assuming you have set the variable to some value
/path, files will be installed into /path/bin,
/path/include/X11, /path/lib, and /path/man."
B. For Vendor-Supplied Distributions
Some third-party vendors distribute derivatives of the X Window
System. If you use a distribution that includes X tools that have
setuid or setgid bits set, then you may need to apply Solution B or C
in Section IV.
If you use a distribution that does not have setuid or setgid bits
enabled on any X tools, then you do not need to take any of the steps
listed below.
Below is a list of vendors who have provided information about this
problem. If your vendor's name is not on this list and you need
clarification, you should check directly with your vendor.
IV. Solution
If any X tools that you are using are potentially vulnerable (see Section
III), we encourage you to take one of the following steps. If the setuid
or setgid bits are not enabled on any of the tools in your distribution,
you do not need to take any of the steps listed below.
For distributions that were built directly from the source code
supplied by The Open Group (and previously by the X Consortium), we
encourage you to apply either Solutions A or C. For vendor-supplied
distributions, we encourage you to apply either Solutions B or C.
A. Upgrade to X11 Release 6.3
If you download and build your own distributions directly from the
source code, we encourage you to install the latest version, X11
Release 6.3. The source code can be obtained from
ftp://ftp.x.org/pub/R6.3/tars/xc-1.tar.gz
ftp://ftp.x.org/pub/R6.3/tars/xc-2.tar.gz
ftp://ftp.x.org/pub/R6.3/tars/xc-3.tar.gz
Note that these distributions are very large. The compressed
files consume about 40M of disk space. The uncompressed tar files
consume about 150M of disk space.
B. Install a patch from your vendor
Below is a list of vendors who have provided information about
this problem. 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)
Digital Equipment Corporation (DEC)
FreeBSD, Inc.
Hewlett-Packard Company
IBM Corporation
NEC Corporation
NeXT Software, Inc.
The Open Group (formerly OSF/X Consortium)
The Santa Cruz Operation, Inc. (SCO)
Sun Microsystems, Inc.
C. Remove the setuid bit from affected programs
If you are unable to apply Solutions A or B, then as a last resort
we recommend removing the setuid or setgid bits from the
executable files in your distribution of X.
Note that this may have an adverse effect on some system
operations. For instance, on some systems the xlock program needs
to have the setuid bit enabled so that the shadow password file
can be read to unlock the screen. By removing the setuid bit from
this program, you remove the ability of the xlock program to read
the shadow password file. This means that particular version of
the xlock program should not be used at all, or it should be
killed from another terminal when necessary.
...........................................................................
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)
=====================================
We released a patch for this for the 2.1 BSD/OS release,
and it's already fixed in our current release.
Digital Equipment Corporation (DEC)
===================================
At the time of writing this document, patches(binary kits) are in progress and
final testing is expected to begin soon. Digital will provide notice of the
completion/availability of the patches through AES services (DIA, DSNlink
FLASH) and be available from your normal Digital Support channel.
FreeBSD, Inc.
=============
We're aware of the problem and are trying to correct it with a new release of
the Xt library.
Hewlett-Packard Company
=======================
HPSBUX9704-058
Description: Security Vulnerability in libXt for HP-UX 9.X & 10.X
HEWLETT-PACKARD SECURITY BULLETIN: #00058 libXt
Security Bulletins are available from the HP Electronic
Support Center via electronic mail.
User your browser to get to the HP Electronic Support
Center page at:
http://us-support.external.hp.com
(for US, Canada, Asia-Pacific, & Latin-America)
http://europe-support.external.hp.com
(for Europe)
IBM Corporation
===============
See the appropriate release below to determine your action.
AIX 3.2
-------
Apply the following fix to your system:
APAR - IX61784,IX67047,IX66713 (PTF - U445908,U447740)
To determine if you have this PTF on your system, run the following
command:
lslpp -lB U445908 U447740
AIX 4.1
-------
Apply the following fix to your system:
APAR - IX61031 IX66736 IX66449
To determine if you have this APAR on your system, run the following
command:
instfix -ik IX61031 IX66736 IX66449
Or run the following command:
lslpp -h X11.base.lib
Your version of X11.base.lib should be 4.1.5.2 or later.
AIX 4.2
-------
Apply the following fix to your system:
APAR - IX66824 IX66352
To determine if you have this APAR on your system, run the following
command:
instfix -ik IX66824 IX66352
Or run the following command:
lslpp -h X11.base.lib
Your version of X11.base.lib should be 4.2.1.0 or later.
To Order
--------
APARs may be ordered using Electronic Fix Distribution (via FixDist)
or from the IBM Support Center. For more information on FixDist,
reference URL:
http://service.software.ibm.com/aixsupport/
or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".
IBM and AIX are registered trademarks of International Business Machines
Corporation.
NEC Corporation
===============
EWS-UX/V(Rel4.2) R7.x - R10.x vulnerable
EWS-UX/V(Rel4.2MP) R10.x vulnerable
UP-UX/V(Rel4.2MP) R5.x - R7.x vulnerable
UX/4800 R11.x - current vulnerable
Patches for this vulnerability are in progress.
For further information, please contact by e-mail:
UX48-security-support@nec.co.jp
NeXT Software, Inc.
===================
X-Windows is not part of any NextStep or OpenStep release. We are not
vulnerable to this problem.
The Open Group (formerly OSF/X Consortium)
================================
Not vulnerable.
The Santa Cruz Operation, Inc. (SCO)
====================================
We are investigating this problem and will provide updated
information for this advisory when it becomes available.
Sun Microsystems, Inc.
======================
We are investigating.
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The CERT Coordination Center staff thanks Kaleb Keithley of The Open Group
for helping us understand the nature and scope of this problem.
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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
- ----------------------------
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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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.
* Registered U.S. Patent and Trademark Office.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.11.libXt
http://www.cert.org
click on "CERT Advisories"
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Revision history
May 8, 1997 Appendix A - updated vendor information for Hewlett-Packard.
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