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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
        cert-advisory-request@cert.org
   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"


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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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