This advisory addresses a buffer overflow condition in some versions of the at(1) program. Patch information and a workaround are provided.
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CERT* Advisory CA-97.18
Original issue date: June 12, 1997
Last Revised: January 5, 1998 - Updated vendor information for Silicon
Graphics, Inc.
A complete revision history is at the end of this file.
Topic: Vulnerability in the at(1) program
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The CERT Coordination Center has received reports of a buffer overflow
condition in some versions of the at(1) program. By carefully specifying the
data that overflows this buffer, any user can execute arbitrary commands as
root.
The CERT/CC team recommends installing a vendor patch if one is available
(see Section III.A). Until you can do so, we recommend disabling at(1) (see
Section III.B).
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
The at(1) program can be used by local users to schedule commands to be
executed at a later time. When those commands are run, they are run as
the user who originally ran at(1). That user will be referred to as the
scheduling user.
As a precaution, the scheduling user's list of commands is stored in a
file in a directory that is not writable by other users. The file's
ownership is changed to that of the scheduling user, and that
information is used to define the identity of the process that runs the
commands when the appointed time arrives. These measures are intended
to prevent other users from changing the scheduling user's list of
commands or creating new lists to be executed as another user. To
achieve this additional level of security, the at(1) program runs as
set-user-id root.
Some versions of at(1) contain a programming defect that can result in a
buffer local to at(1) being overflowed. Through the careful specification
of the data that overflows this buffer, arbitrary commands can be executed
with the identity of at(1) process, root in this case.
II. Impact
Any user with an account on a system that contains a defective version
of at(1) can execute programs as root.
III. Solution
A. Install a patch from your vendor
Below is a list of vendors who have provided information about
at. 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
Hewlett-Packard Company
IBM Corporation
NCR Corporation
Santa Cruz Operation, Inc. (SCO)
Silicon Graphics, Inc.
Sun Microsystems, Inc.
B. Until you are able to install the appropriate patch, we recommend
the following workaround:
Turn off at(1) by setting its mode to 0. Do the following as
root:
# chmod 0 /usr/bin/at
Note that the location of at(1) varies from system to system.
Consult your system's documentation for the correct location.
After you turn off the at(1) command, users will not be able to use
it. As an alternative to at(1), consider using the crontab(1)
command if your system provides it.
...........................................................................
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)
=====================================
No versions of BSD/OS are susceptible to this problem.
Cray Research - A Silicon Graphics Company
==========================================
Neither Unicos nor Unicos/mk is believed to be vulnerable.
Data General Corporation
=============================
No versions of DG/UX are vulnerable to this problem.
Digital Equipment Corporation
=============================
Copyright (c) Digital Equipment Corporation 1997. All rights
reserved.
Information about this reported problem, and subsequent attempts to
reproduce the problem have been unsuccessful for Digital's ULTRIX or
Digital UNIX Operating Systems Software. Should further information or
testing indicate this problem can be reproduced on Digital's
products, a solution will be provided accordingly. At that time 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.
DIGITAL EQUIPMENT CORPORATION 6/09/97
----------------------------- ----------
Hewlett-Packard Company
=======================
Hewlett Packard has published information relating to this problem in
Security Bulletin #00023. It is available from the HP Electronic Support
Center. The center's Web page is at
http://us-support.external.hp.com
(for US, Canada, Asia-Pacific, and 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 fixes to your system:
PTF - U443452 U443486 U444191 U444206 U444213 U444243
APAR - IX60796
To determine if you have these PTFs on your system, run the following
commands:
lslpp -lB U443452 U443486 U444191 U444206 U444213 U444243
AIX 4.1
-------
Apply the following fixes to your system:
APAR - IX60894
APAR - IX60890
To determine if you have this APAR on your system, run the following
commands:
instfix -ik IX60894
instfix -ik IX60890
Or run the following commands:
lslpp -h bos.rte.cron
lslpp -h bos.rte.libc
Your version of bos.rte.cron should be 4.1.4.8 or later.
Your version of bos.rte.libc should be 4.1.4.18 or later.
AIX 4.2
-------
Apply the following fixes to your system:
APAR - IX60892
APAR - IX61125
To determine if you have this APAR on your system, run the following
commands:
instfix -ik IX60892
instfix -ik IX61125
Or run the following commands:
lslpp -h bos.rte.cron
lslpp -h bos.rte.libc
Your version of bos.rte.cron should be 4.2.0.1 or later.
Your version of bos.rte.libc should be 4.2.0.5 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.
NCR Corporation
===============
The at binary that ships with some NCR MP-RAS SVR4 releases contains
a vulnerability that could allow a user to execute random commands as
root.
NCR is delivering a set of operating system dependent patches which
contain a new version of the at command. Accompanying each patch is
a README file which discusses the general purpose of the patch and
describes how to apply it to your system.
Recommended solution:
Apply one of the following patches based on your operating system
revision:
MP-RAS 3.00.x - PBASEI300 (Version after 8/18-97)
MP-RAS 3.01.x - PBASEE300 (Version after 8/26-97)
MP-RAS 3.02.x and later - Not vulnerable
The patches described above provide a new version of the at
executable, which fixes the vulnerability.
Santa Cruz Operation, Inc. (SCO)
================================
All SCO operating systems are vulnerable. SCO has made an interim fix
available for anonymous ftp:
ftp://ftp.sco.com/SSE/sse007.ltr.Z - cover letter
ftp://ftp.sco.com/SSE/sse007.tar.Z - replacement binaries
The fix includes binaries for the following SCO operating systems:
- SCO CMW+ 3.0
- SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4
- SCO OpenServer 5.0
- SCO UnixWare 2.1
Silicon Graphics, Inc.
======================
Silicon Graphics Inc. has investigated the issue and recommends the
following steps for neutralizing the exposure. It is HIGHLY RECOMMENDED
that these measures be implemented on ALL SGI systems. This issue will
be corrected in future releases of IRIX.
For further information, please refer to Silicon Graphics
Inc. Security Advisory Number: 19971102-01-PX, "Vulnerability in at(1)
program."
The SGI anonymous FTP site is sgigate.sgi.com (204.94.209.1) or its
mirror, ftp.sgi.com. Security information and patches can be found
in the ~ftp/security and ~ftp/patches directories, respectfully.
Sun Microsystems, Inc.
======================
Bulletin Number: #00160
Date: December 3, 1997
Sun security bulletins are available via World Wide Web at:
<URL:http://sunsolve.sun.com/sunsolve/secbulletins>
The following patches are available in relation to the at problem.
OS version Patch ID
__________ ________
SunOS 5.5.1 103690-05
SunOS 5.5.1_x86 103691-05
SunOS 5.5 103723-05
SunOS 5.5_x86 103724-05
SunOS 5.4 102693-05
SunOS 5.4_x86 102694-05
SunOS 5.3 101572-08
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Technical information for this advisory was drawn in part from a posting by
Don Farmer to the bugtraq mailing list. Thanks to Wolfgang Ley of DFN-CERT for
his help in developing 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
- ----------------------------
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
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In the subject line, type
SUBSCRIBE your-email-address
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Copyright 1997 Carnegie Mellon University. Conditions for use, disclaimers,
and sponsorship information can be found in
http://www.cert.org/legal_stuff.html and ftp://ftp.cert.org/pub/legal_stuff .
If you do not have FTP or web access, send mail to cert@cert.org with
"copyright" in the subject line.
CERT is registered in the U.S. Patent and Trademark Office.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.18.at
http://www.cert.org
click on "CERT Advisories"
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Revision history
Jan. 5, 1998 Updated vendor information for Silicon Graphics, Inc.
Dec. 5, 1997 Updated vendor information for NCR Corporation and Sun
Microsystems, Inc.
Sep. 30, 1997 Updated copyright statement
Aug. 28, 1997 Section III and Appendix A - added vendor information
for NCR Corporation.
Aug. 16, 1997 Appendix A - added Data General information.
July 14, 1997 Appendix A - updated Hewlett-Packard information.
June 25, 1997 Section IIIA and Appendix A - Added vendor information
for Berkeley Software Design, Inc. (BSDI).
June 12, 1997 Section IIIA and Appendix A - Added vendor information
for Digital Equipment Corporation.
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