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            AUSCERT External Security Bulletin Redistribution
                                      
                                      
       ESB-98.022 -- IBM-ERS Security Vulnerability Alert #1998:003.1
               Telnet denial of service attack vulnerability 
                             12 February 1998

===========================================================================

The IBM Emergency Response Service has released the following alert
concerning a denial of service attack that causes all tty activity to hang
and prevents new telnet sessions from being established.  This
vulnerability may allow remote users to cause the system to hang.

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.

NOTE: This is only the original release of the security bulletin.  It will
not be updated when the original bulletin is.  If downloading at a later
date, it is recommended that the bulletin is retrieved from the original
authors to ensure that the information is still current.

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

Previous advisories and external security bulletins can be retrieved from:

        http://www.auscert.org.au/Information/advisories.html

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

Internet Email: auscert@auscert.org.au
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AUSCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for emergencies.
Facsimile:      (07) 3365 7031


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                           EMERGENCY RESPONSE SERVICE
                          SECURITY VULNERABILITY ALERT

11 February 1998 13:30 GMT                       Number: ERS-SVA-E01-1998:003.1
===============================================================================
                             VULNERABILITY  SUMMARY

VULNERABILITY:  Telnet denial of service attack

PLATFORMS:      IBM AIX(r) 4.1.x, 4.2.x, 4.3

SOLUTION:       Apply the fixes listed below.

THREAT:         Remote users can cause the system to hang.

===============================================================================
                              DETAILED INFORMATION

I.  Description

A denial of service attack has been posted to the Bugtraq mailing list
that causes all tty activity to hang and prevents new telnet sessions
from being established.

II.  Impact

Remote users can cause the system to run out of message blocks and
hang.

III.  Solutions

  A.  Official fix

      At this time, only the AIX 4.1.x APAR is available.  AIX 4.2.x
      and 4.3.0 customers can apply the temporary fix listed below
      until the official APARs are available.  There are no fixes
      planned for AIX 3.2.5 or earlier.  It is recommended that version
      3 customers upgrade to version 4.

      AIX 4.1.x:  IX73427   (bos.rte.tty 4.1.5.20)   -- available now
      AIX 4.2.x:  IX73580
      AIX 4.3.0:  IX73214

  B.  How to alleviate the problem

      A temporary fix is available for AIX 4.2.x and AIX 4.3.0 via
      anonymous ftp from:

        ftp://aix.software.ibm.com/aix/efixes/security/ldterm_fix.tar.Z

      Filename          sum             md5
      ===================================================================
      ldterm.42         52419    77     7ec3ff7eb83ded8f50219a838a0a4c0b
      ldterm.43         37579    77     f066b7d6c3a845c892941a7ab15a6e60
      ldterm_fix.sh     10210     3     e3a8bbecda52ff68391657f008b46262

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

      1.  Use the following command to determine the version of the
          bos.rte.tty fileset on your machine.

        # lslpp -l bos.rte.tty

          If the version is not at the level described below, install
          the requisite APAR for your release.  This will help ensure
          that the efix binary will run properly.

          Release       bos.rte.tty version       requisite APAR
          =============================================================
          AIX 4.2.x     less than 4.2.1.9         install IX73755
          AIX 4.3.0     less than 4.3.0.3         install IX73397

      2.  Uncompress and extract the fix.

        # uncompress < ldterm_fix.tar.Z | tar xf -
        # cd ldterm_fix

      3.  Run the ldterm_fix.sh script to install the new tty driver.

        # ./ldterm_fix.sh

      4.  Reboot.

      NOTE: This temporary fix has not been fully regression tested.

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

        http://service.software.ibm.com/aixsupport/

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

V.  Acknowledgements

Thanks to Kevin Ruderman <rudi@bu.edu> for bringing this problem to our
attention.

VI.  Contact Information

Comments regarding the content of this announcement can be directed to
the IBM Support Center or to:

   security-alert@austin.ibm.com

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 a registered trademark 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
security products and services.  From hardware to software to consulting,
SecureWay solutions can give you the assurance and expertise you need to
protect your valuable business resources.  To find out more about the IBM
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,
team contact information, and other items.

IBM-ERS uses Pretty Good Privacy* (PGP*) as the digital signature mechanism for
security vulnerability alerts and other distributed information.  The IBM-ERS
PGP* public key is available from http://www.ers.ibm.com/team-info/pgpkey.html.
"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 1998 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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