TUCoPS :: Unix :: General :: ciach074.txt

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[ For Public Release ]
 __________________________________________________________
 The U.S. Department of Energy
 Computer Incident Advisory Capability
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 __________________________________________________________
 INFORMATION BULLETIN
 Unix lpr Buffer Overrun Vulnerability
 (Update to vendor patches H-08)
June 25, 1997 16:00 GMT Number H-74
______________________________________________________________________________
PROBLEM: A vulnerability exists in the BSD-based lpr printing package
 found on many Unix systems.
PLATFORM: A variety of Unix platforms.
DAMAGE: This vulnerability may allow local users to gain root
 privileges.
SOLUTION: Until vendor patches are available it is recommend that you
 apply the wrapper described below.
______________________________________________________________________________
VULNERABILITY Exploit information and patches involving this vulnerability
ASSESSMENT: have been publicly available for some time. Recently, the
 CERT/CC has received reports that the vulnerability is being
 actively exploited.
______________________________________________________________________________
[ Start CERT Advisory ]
=============================================================================
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.
- ----------------------------------------------------------------------------
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.
- -----------------------------------------------------------------------------
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.
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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.
- ----------------------------------------------------------------------------
[ End CERT Advisory ]
______________________________________________________________________________
CIAC wishes to acknowledge the contributions of CERT & others for the
information contained in this bulletin.
______________________________________________________________________________
CIAC, the Computer Incident Advisory Capability, is the computer
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