============================================================================= CERT(sm) Advisory CA-96.03 February 21, 1996 Topic: Vulnerability in Kerberos 4 Key Server ----------------------------------------------------------------------------- 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. As we receive additional information relating to this advisory, we will place it in: ftp://info.cert.org/pub/cert_advisories/CA-96.03.README We encourage you to check our README files regularly for updates on advisories that relate to your site. ----------------------------------------------------------------------------- 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. 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 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 put all vendor information in the CA-96.03.README file, updating that file as we hear from vendors. --------------------------------------------------------------------------- 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. --------------------------------------------------------------------------- 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 ------------------------ 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. ......................................................................... 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 advisory. 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.