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CERT Advisory 108
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CERT(sm) Advisory CA-96.03
Original issue date: February 21, 1996
Last revised: August 30, 1996
Information previously in the README was inserted
into the advisory.
A complete revision history is at the end of this advisory.
Topic: Vulnerability in Kerberos 4 Key Server
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The CERT Coordination Center has received reports of a vulnerability in the
Kerberos Version 4 server. On unpatched Kerberos 4 systems, under certain
circumstances, intruders can masquerade as authorized Kerberos users and gain
access to services and resources not intended for their use. The CERT team
recommends that you apply one of the solutions given in Section III.
The Kerberos Version 5 server running in Version 4 compatibility mode is also
vulnerable under certain circumstances. The Massachusetts Institute of
Technology (MIT) is working on the patches for that version.
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 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 athena-dist.mit.edu. 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
proceeding.
As of February 23, 1996, MIT has updated the patch described in
advisory CA-96.03. The actual patch has not changed, but the
README.PATCH file (part of random_patch.tar.*) which contains
instructions on how to install the patch has been edited to include
the following new paragraph:
>IMPORTANT: After running fix_kdb_keys you must kill and restart the
>kerberos server process (it has the old keys cached in memory). Also,
>if you operate any Kerberos slave servers, you need to perform a slave
>propagation immediately to update the keys on the slaves.
Updated files are now available on "athena-dist.mit.edu"
including an updated random_patch.md5 file which contains the MD5
checksums of random_patch.tar.* The PGP Signature is issued by
Jeffrey I. Schiller <jis@mit.edu> using PGP keyid 0x0DBF906D. The
fingerprint is
DD DC 88 AA 92 DC DD D5 BA 0A 6B 59 C1 65 AD 01
The updated files are also available from
ftp://info.cert.org/pub/vendors/mit/Patches/Kerberos-V4/
The new checksums are
MD5 (random_patch.md5) = ecf5412094572e183aa33ae4e5f197b8
MD5 (random_patch.tar.Z) = e925b687a05a8c6321b2805026253315
MD5 (random_patch.tar.gz) = 003226914427094a642fd1f067f589d2
These files are also available from
ftp://info.cert.org/pub/vendors/mit/Patches/Kerberos-V4/random_patch.md5
ftp://info.cert.org/pub/vendors/mit/Patches/Kerberos-V4/random_patch.tar.Z
ftp://info.cert.org/pub/vendors/mit/Patches/Kerberos-V4/random_patch.tar.gz
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 update the appendix as we hear from vendors.
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Appendix A: Vendor Information
Below is information we have received from vendors concerning the
vulnerability described in this advisory. If you do not see your vendor's
name, please contact the vendor directly for information.
The Santa Cruz Operation, Inc.
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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.
TGV Software, Inc.
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TGV has made two Kerberos ECO kits available (one for MultiNet V3.4
and one for V3.5) for Anonymous FTP. If you are running Kerberos, we
_strongly_ urge you to apply this kit.
To obtain the kit, FTP to ECO.TGV.COM, username ANONYMOUS, password
either KERBEROS-034 or KERBEROS-035 (depending on the version of
MultiNet that you are running) and download the ECO kit:
ftp://anonymous:kerberos-035@eco.tgv.com
The kit is available in both VMS BACKUP save set format as well as in
a compressed .ZIP file. Use VMSINSTAL to apply the ECO.
Once you have completed the upgrade, the KITREMARK.VUR file from
the ECO kit will be displayed providing instructions during the
installation process.
If you have any questions, please send an e-mail message to
MultiNet-VMS@Support.TGV.COM
Transarc Corporation
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Kerberos Version 4.0 is used in our AFS product (all versions
of AFS), while Kerberos Version 5.0 is used in our DCE product
(Kerberos Version 5.0 is used in ALL DCE products).
In light of the COAST work, Transarc is doing a security review of
Kerberos 4.0 and AFS. We expect to provide some procedural changes to
improve security in new cells, and we will make code changes as
necessary. OSF also reviewed Kerberos 5.0, and they have released a
source patch for Kerberos 5.0 that strengthens the random number
generator in Kerberos 5.0. This patch is relevant to all versions of
DCE (but not to AFS since it is based on Kerberos 4.0).
Transarc has this OSF patch available for DCE 1.1 on Solaris 2.4, DCE
1.0.3a on Solaris 2.4, DCE 1.0.3a on Solaris 2.3, and DCE 1.0.3a on
Sun OS 4.1.3. Please contact Transarc Customer Support for access to
these patches.
Please feel free to contact me directly if you have further questions
about this issue.
For pointers and background on these issues please refer to
http://www.transarc.com/afs/transarc.com/public/www/Public/Support/security-\
update.html
Liz Hines
Hines@transarc.com
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The CERT Coordination Center thanks Jeffrey Schiller and Theodore Ts'o of
Massachusetts Institute of Technology for their effort in responding to this
problem, and thanks Gene Spafford of COAST for the initial information about
the problem.
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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 (FIRST).
We strongly urge you to encrypt any sensitive information you send by email.
The CERT Coordination Center can support a shared DES key and PGP. Contact the
CERT staff for more information.
Location of CERT PGP key
ftp://info.cert.org/pub/CERT_PGP.key
CERT Contact Information
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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
To be added to our mailing list for CERT advisories and bulletins, send your
email address to
cert-advisory-request@cert.org
CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
comp.security.announce
Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided it
is used for noncommercial purposes and the copyright statement is included.
CERT is a service mark of Carnegie Mellon University.
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Revision history
Aug. 30, 1996 Information previously in the README was inserted into the
advisory.
Mar. 08, 1996 Appendix, TGV Software & Transarc - added entries
Feb. 23, 1996 Sec. III.A - noted a change in the readme.patch file and put
new MD5 checksums at the end of the section.
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