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CERT Advisory 151
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CERT* Advisory CA-97.19
Original issue date: June 25, 1997
Last revised: --
Topic: lpr Buffer Overrun Vulnerability
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The technical content of this advisory was
originally published by AUSCERT (AA-96.12),
who last updated the information on June 19, 1997.
We use it here with their permission.
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There is a vulnerability in the BSD-based printing software, lpr, available on
a variety of Unix platforms. This vulnerability may allow local users to gain
root privileges.
Exploit information involving this vulnerability has been publicly available
for some time. Recently, the CERT/CC has received reports that the
vulnerability is being actively exploited.
We recommend installing a vendor patch if one is available. Until you can do
so, we recommend using the wrapper 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
A vulnerability exists in the BSD-based lpr printing package found on many
Unix systems.
Due to insufficient bounds checking on arguments that are supplied by
users, it is possible to overwrite the internal stack space of the lpr
program while it is executing. This can allow an intruder to cause lpr to
execute arbitrary commands by supplying a carefully designed argument to
lpr. These commands will be run with the privileges of the lpr program.
When lpr is installed setuid or setgid, it may allow intruders to gain
those privileges.
When lpr is setuid root, it may allow intruders to run arbitrary commands
with root privileges.
For information from vendors relating to this vulnerability, please check
Appendix A of this advisory. In addition to the products mentioned, be
aware that platforms using the BSD-based lpr systems, in which lpr is
installed setuid or setgid, may also be vulnerable.
Note also that the vulnerability described in this advisory is not present
in the LPRng printing package.
II. Impact
Local users may gain root privileges. It is necessary to have access to an
account on the system to exploit this vulnerability.
III. Solution
The lpr printing package is available on many different systems. As vendor
patches are made available sites are encouraged to install them. Until
vendor patches are available, we recommend applying the workaround
referred to in III.B.
A. Install vendor patches
Specific vendor information has been placed in Appendix A. If the BSD-
based lpr printing software is used and your vendor is not listed in
Appendix A, please contact your vendor directly.
B. Install lpr wrapper
Until you can install a vendor patch, we encourage you install a
wrapper developed by AUSCERT to help prevent lpr being exploited using
this vulnerability.
The source for the wrapper, including installation instructions, can be
found at
ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/overflow_wrapper.c
This wrapper replaces the lpr program and checks the length of the
command line arguments which are passed to it. If an argument exceeds a
certain predefined value (MAXARGLEN), the wrapper exits without
executing the lpr command. The wrapper program can also be configured
to syslog any failed attempts to execute lpr with arguments exceeding
MAXARGLEN. For further instructions on using this wrapper, please read
the comments at the top of overflow_wrapper.c.
When compiling overflow_wrapper.c for use with lpr, AUSCERT recommends
defining MAXARGLEN to be 32.
The MD5 checksum for the current version of overflow_wrapper.c can be
retrieved from
ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM
The CHECKSUM file has been digitally signed using the AUSCERT PGP key.
...........................................................................
Appendix A Vendor information
Below is a list of the vendors who have provided information. We will update
this appendix as we receive additional information. If you do not see your
vendor's name, please contact the vendor directly.
Berkeley Software Design, Inc. (BSDI)
======================================
BSD/OS 3.0 is not vulnerable to the problem.
BSDI have issued a patch which addresses this vulnerability under
BSD/OS 2.1. This patch is available from:
ftp://ftp.bsdi.com/pub/bsdi/patches/patches-2.1/U210-028
Digital Equipment Corporation
=============================
Digital Equipment Corporation
Software Security Response Team
Copyright (c) Digital Equipment Corporation 1997. All rights reserved.
This reported problem is not present for Digital's ULTRIX or
Digital UNIX Operating Systems Software.
- DIGITAL EQUIPMENT CORPORATION 06/19/97
FreeBSD
=======
This problem was fixed prior to the release of FreeBSD 2.1.6 and 2.2.
Users running older versions of the OS should review the security
advisory describing this vulnerability (SA-96.18) at:
ftp://freebsd.org/pub/CERT/advisories/FreeBSD-SA-96:18.lpr.asc
Patches can be found in the directory:
ftp://freebsd.org/pub/CERT/patches/SA-96:18
IBM Corporation
===============
AIX is not vulnerable to the lpr buffer overflow. The version of lpr
shipped with AIX is not installed with the setuid bit turned on.
IBM and AIX are registered trademarks of International Business Machines
Corporation.
Linux
=====
The Linux Emergency Response Team have released a Linux Security FAQ
Update which addresses this vulnerability. This Update contains
information regarding various Linux distributions.
It is available from:
ftp://bach.cis.temple.edu/pub/Linux/Security/FAQ/updates/
Update-11-25-1996.vulnerability-lpr-0.06-v1.2
NeXT
====
The NeXT group has addressed the vulnerability described in this advisory
in release 4.2 of OpenStep/Mach.
The Santa Cruz Operation, Inc. (SCO)
====================================
SCO has determined that the following SCO operating systems
are not vulnerable:
- SCO CMW+ 3.0
- SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4
- SCO OpenServer 5.0
- SCO UnixWare 2.1
Sun Microsystems, Inc.
=====================
All versions of Solaris are not affected. SunOS 4.1.3_U1 and SunOS 4.1.4
are vulnerable. Sun recommends that sites using SunOS 4.1.3_U1 and SunOS
4.1.4 apply the workaround provided in this advisory.
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The CERT Coordination Center staff thanks AUSCERT for permission to republish
the information in their advisory AA-96.12. AUSCERT originally thanked
Alexander O. Yuriev, the FreeBSD security team, IBM, and the CERT/CC for their
assistance in the production of their 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-97.19.bsdlp
http://www.cert.org
click on "CERT Advisories"
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Revision history
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