AUSCERT External Security Bulletin Redistribution

               ESB-97.130 -- IBM security vulnerability alert
                   Buffer overflow in the "xdat" command
                              22 October 1997


IBM-ERS has released the following advisory concerning a buffer overflow
vulnerability in the xdat command under IBM AIX(r) 4.1, 4.2.  This
vulnerability may allow local users to gain root access.

The following security bulletin is provided as a service to AUSCERT's
members.  As AUSCERT did not write this document, AUSCERT has had no
control over its content.  As such, the decision to use any or all of this
information is the responsibility of each user or organisation, and should
be done so in accordance with site policies and procedures.

Contact information for IBM-ERS is included in the Security Bulletin below.
If you have any questions or need further information, please contact them

Previous advisories and external security bulletins can be retrieved from:


If you believe that your system has been compromised, contact AUSCERT or
your representative in FIRST (Forum of Incident Response and Security

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 4477
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                           EMERGENCY RESPONSE SERVICE

21 October 1997 16:00 GMT                        Number: ERS-SVA-E01-1997:004.1
                             VULNERABILITY  SUMMARY

VULNERABILITY:	Buffer overflow in the IBM AIX "xdat" command

PLATFORMS:	IBM AIX(r) 4.1, 4.2

SOLUTION:	Remove the setuid bit or apply one of the fixes below

THREAT:		Local users may become root

                              DETAILED INFORMATION

I. Description

The "xdat" command shipped with AIX version 4 does not check the length of the
"TZ" environment variable.  This command was not shipped with AIX 3.2.

II. Impact

Local users may become root.

III. Solutions

  A.  How to alleviate the problem

      This problem can be alleviated by removing the set-user-id bit from the
      "xdat" program.  To do this, execute the following command as "root":

          chmod 555 /usr/lpp/X11/bin/xdat

  B.  Official fix

      IBM is currently working on the following APARs but they are not yet

      AIX 4.1:  IX72020
      AIX 4.2:  IX72021

  C.  Temporary fixes

      A temporary fix is available via anonymous ftp from:


      Filename      sum               md5
      xdat          44047    74       33bcec8bbc7d8eb2e4e2ae760d2b986e

      Use the following steps (as root) to install the temporary fix:

      1.  Uncompress and extract the fix:

        # uncompress < security.xdat.tar.Z | tar xf -

      2.  Use the "xdat_patch.sh" script or the following manual commands:      

        # pgp xdat/xdat.pgp xdat/xdat
        # cp /usr/lpp/X11/bin/xdat /usr/lpp/X11/bin/xdat.orig
        # chmod -s /usr/lpp/X11/bin/xdat.orig
        # cp xdat/xdat /usr/lpp/X11/bin/xdat
        # chmod 4555 /usr/lpp/X11/bin/xdat

      This fix has not been fully regression tested but does prevent the TZ
      environment variable exploit.  If the new executable fails to load due
      to missing symbols, the following APARs may help to resolve the

         AIX 4.1:  IX69580
         AIX 4.2:  IX69180

IV. Obtaining Fixes

IBM AIX APARs may be ordered using Electronic Fix Distribution (via the FixDist
program), or from the IBM Support Center.  For more information on FixDist,
and to obtain fixes via the Internet, please reference


or send electronic mail to "aixserv@austin.ibm.com" with the word "FixDist" in
the "Subject:" line.

V. Acknowledgements

Thanks to Bryan Self <bryan@scott.net> for bringing this problem to our

VI. AIX Security Contact Information

To request the PGP public key that can be used to encrypt new AIX security
vulnerabilities, send email to security-alert@austin.ibm.com with a subject
of "get key".

If you would like to subscribe to the AIX security newsletter, send a note
to aixserv@austin.ibm.com with a subject of "subscribe Security".  To cancel
your subscription, use a subject of "unsubscribe Security".  To see a list of
other available subscriptions, use a subject of "help".

IBM and AIX are registered trademarks of International Business Machines
Corporation.  All other trademarks are property of their respective holders.


IBM's Internet Emergency Response Service (IBM-ERS) is a subscription-based
Internet security response service that includes computer security incident
response and management, regular electronic verification of your Internet
gateway(s), and security vulnerability alerts similar to this one that are
tailored to your specific computing environment.  By acting as an extension
of your own internal security staff, IBM-ERS's team of Internet security
experts helps you quickly detect and respond to attacks and exposures across
your Internet connection(s).

As a part of IBM's Business Recovery Services organization, the IBM Internet
Emergency Response Service is a component of IBM's SecureWay(tm) line of
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SecureWay solutions can give you the assurance and expertise you need to
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Internet Emergency Response Service, send an electronic mail message to
ers-sales@vnet.ibm.com, or call 1-800-742-2493 (Prompt 4).

IBM-ERS maintains a site on the World Wide Web at http://www.ers.ibm.com/.
Visit the site for information about the service, copies of security alerts,
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IBM-ERS uses Pretty Good Privacy* (PGP*) as the digital signature mechanism for
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"Pretty Good Privacy" and "PGP" are trademarks of Philip Zimmermann.

IBM-ERS is a Member Team of the Forum of Incident Response and Security Teams
(FIRST), a global organization established to foster cooperation and response
coordination among computer security teams worldwide.

Copyright 1997 International Business Machines Corporation.

The information in this document is provided as a service to customers of
the IBM Emergency Response Service.  Neither International Business Machines
Corporation, Integrated Systems Solutions Corporation, nor any of their
employees, makes any warranty, express or implied, or assumes any legal
liability or responsibility for the accuracy, completeness, or usefulness of
any information, apparatus, product, or process contained herein, or
represents that its use would not infringe any privately owned rights.
Reference herein to any specific commercial products, process, or service by
trade name, trademark, manufacturer, or otherwise, does not necessarily
constitute or imply its endorsement, recommendation or favoring by IBM or
its subsidiaries.  The views and opinions of authors expressed herein do not
necessarily state or reflect those of IBM or its subsidiaries, and may not be
used for advertising or product endorsement purposes.

The material in this security alert may be reproduced and distributed,
without permission, in whole or in part, by other security incident response
teams (both commercial and non-commercial), provided the above copyright is
kept intact and due credit is given to IBM-ERS.

This security alert may be reproduced and distributed, without permission,
in its entirety only, by any person provided such reproduction and/or
distribution is performed for non-commercial purposes and with the intent of
increasing the awareness of the Internet community.


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