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TUCoPS :: Unix :: General :: ciacg013.txt

Kerberos V4 Vulnerability


                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                      Kerberos 4 Key Server Vulnerability

February 23, 1996 15:00 GMT                                        Number G-13
PROBLEM:       A problem with Kerberos Version 4. 
PLATFORM:      Kerberos Version 4 Server and/or Kerberos Version 5 Server
               running in Version 4 compatibility mode. 
DAMAGE:        Intruders can masquerade as authorized Kerberos users and gain 
               access to services and resources not intended for their use. 
SOLUTION:      Install proper patch depending on source or binary 
VULNERABILITY  Knowledge of how to exploit this vulnerability is becoming  
ASSESSMENT:    widely known.                                                               

CIAC has obtained information from COAST describing a vulnerability in
the Kerberos Version 4. If you are currently running Kerberos Version 4
server, you should install the proper patch.

[ Start of COAST Notification ]
Personnel at the COAST Laboratory (Computer Operations, Audit, and
Security Technology) at Purdue University have discovered some
unexepected weaknesses in the Kerberos security system.  Graduate
students Steve Lodin and Bryn Dole, working with Professor Eugene
Spafford, have discovered a method whereby someone without privileged
access to most implementations of a Kerberos 4 server can nonetheless
break secret session keys issued to users.  This means that it is
possible to gain unauthorized access to distributed services available
to a user without knowing that user's password. This method has been
demonstrated to work in under 5 minutes, on average, using a typical
workstation, and sometimes as quickly as 12 seconds.

{text deleted}

COAST personnel have been informed that MIT has already developed a
fix for the flaw in version 4 Kerberos and is preparing it for
release.  Additionally, COAST researchers are cooperating with MIT
personnel to identify what (if any) fixes are necessary for version 5
Kerberos. Users of either version of Kerberos should contact their
vendors for details of any fixes that may be made available; vendors
of products incorporating Kerberos should contact MIT directly for
details of the problems and fixes.

[ End COAST Notification]

[  Start CERT Bulletin ]

I.   Description

     The Kerberos Version 4 server is using a weak random number generator
     to produce session keys. On a computer of average speed, the session key
     for a ticket can be broken in a maximum of 2-4 minutes, and sometimes in
     much less time. This means that usable session keys can be manufactured
     without a user first being authorized by Kerberos.

II.  Impact

     Under certain circumstances, intruders can masquerade as authorized
     Kerberos users and gain access to services and resources not intended for
     their use. 

III. Solution
     If you are running Kerberos Version 4 and have built Kerberos from a
     source distribution, use solution A. If you have obtained Kerberos 4
     binaries from a vendor, use solution B. If you are now using Kerberos
     Version 5, be aware that MIT is working on patches for that version.
     Notice will be made when the patches are available.

     A. Solution for Source Distributions

        If you have built Kerberos Version 4 from source, follow these
        instructions to retrieve the fixes necessary to correct this problem:
          Use anonymous FTP to Change directory to
          /pub/kerberos, fetch and read "README.KRB4" found in that
          directory. It will provide the name of the distribution directory
          (which is otherwise hidden and cannot be found by listing its
          parent directory). Change directory to the hidden distribution
          directory. There you will find the original Kerberos distribution
          plus a new file named "random_patch.tar.Z" (and random_patch.tar.gz
          for those with "gzip"). This tar file contains two files, the patch
          itself and a README.PATCH file. Read this file carefully before

          The distribution hidden directory also contains a file
          "random_patch.md5" which is a PGP clear-signed file containing the
          MD5 checksums of random_patch.tar.Z and random_patch.tar.gz.

          The PGP Signature is issued by Jeffrey I. Schiller <>
          using PGP keyid 0x0DBF906D. The fingerprint is

                DD DC 88 AA 92 DC DD D5  BA 0A 6B 59 C1 65 AD 01
          The MD5 checksums for these files are

                MD5 (random_patch.md5) = 9b9e3faac75f235cf967f595226192aa
                MD5 (random_patch.tar.Z) = 265e43ad0a055e610a0ba601141a47d4
                MD5 (random_patch.tar.gz) = 9b0d209f74c89b8395b156299fe7df79

   These files are also available from
          The checksums are the same as above.

     B. Solution for Binary Distributions

        Contact your vendor. 
        Some vendors who provide Kerberos are sending the CERT Coordination
        Center information about their patches. Thus far, we have received
        information from one vendor and placed it in the appendix of this
        advisory. We will put all vendor information in the CA-96.03.README
        file, updating that file as we hear from vendors. 

Appendix A: Vendor Information

Current as of February 21, 1996
See CA-96.03.README for updated information.

Below is information we have received from vendors concerning the
vulnerability described in this bulletin. If you do not see your vendor's
name, please contact the vendor directly for information.

The Santa Cruz Operation, Inc.
The Kerberos 4 problem does not affect SCO.

SCO OpenServer, SCO Open Desktop, SCO UnixWare, SCO Unix, and SCO Xenix
do not support Kerberos.

The SCO Security Server, an add-on product for SCO OpenServer 3 and SCO
OpenServer 5, supports Kerberos V5 authentication. This product cannot be
configured to be Kerberos V4 compatible; therefore, it is not vulnerable.

[ End CERT Bulletin ]


CIAC wishes to acknowledge the contributions of COAST, MIT, and CERT for the 
information contained in this bulletin.

CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy (DOE) and the
National Institute of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding member of
FIRST, the Forum of Incident Response and Security Teams, a global organization
established to foster cooperation and coordination among computer security 
teams worldwide.

CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be
contacted at:
    Voice:    +1 510-422-8193
    FAX:      +1 510-423-8002
    STU-III:  +1 510-423-2604

For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH
may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call the
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Previous CIAC notices, anti-virus software, and other information are
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This document was prepared as an account of work sponsored by an agency of the
United States Government. Neither the United States Government nor the
University of California nor any of their employees, makes any warranty,
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