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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

- -----------------------------------------------------------------------------

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.



- -----------------------------------------------------------------------------



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:



        http://ftp.sco.com/SSE/sse007.ltr.Z - cover letter

        http://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:



        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



- -----------------------------------------------------------------------------

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.

- -----------------------------------------------------------------------------



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

         http://info.cert.org/pub/CERT_PGP.key



Getting security information

   CERT publications and other security information are available from

        http://www.cert.org/

        http://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



- ------------------------------------------------------------------------------



Copyright 1997 Carnegie Mellon University. Conditions for use, disclaimers,

and sponsorship information can be found in

http://www.cert.org/legal_stuff.html and http://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.



- ---------------------------------------------------------------------------



This file: http://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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