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CERT Advisory CA-2002-28 Trojan Horse Sendmail Distribution

   Original release date: October 08, 2002
   Last revised: --
   Source: CERT/CC

   A complete revision history is at the end of this file.

Overview

   The CERT/CC has received confirmation that some copies of the source
   code for the Sendmail package were modified by an intruder to contain
   a Trojan horse.

   Sites that employ, redistribute, or mirror the Sendmail package should
   immediately verify the integrity of their distribution.

I. Description

   The CERT/CC has received confirmation that some copies of the source
   code for the Sendmail package have been modified by an intruder to
   contain a Trojan horse.

   The following files were modified to include the malicious code:

     sendmail.8.12.6.tar.Z
     sendmail.8.12.6.tar.gz

   These files began to appear in downloads from the FTP server
   ftp.sendmail.org on or around September 28, 2002. The Sendmail
   development team disabled the compromised FTP server on October 6,
   2002 at approximately 22:15 PDT. It does not appear that copies
   downloaded via HTTP contained the Trojan horse; however, the CERT/CC
   encourages users who may have downloaded the source code via HTTP
   during this time period to take the steps outlined in the Solution
   section as a precautionary measure.

   The Trojan horse versions of Sendmail contain malicious code that is
   run during the process of building the software. This code forks a
   process that connects to a fixed remote server on 6667/tcp. This
   forked process allows the intruder to open a shell running in the
   context of the user who built the Sendmail software. There is no
   evidence that the process is persistent after a reboot of the
   compromised system. However, a subsequent build of the Trojan horse
   Sendmail package will re-establish the backdoor process.

II. Impact

   An intruder operating from the remote address specified in the
   malicious code can gain unauthorized remote access to any host that
   compiled a version of Sendmail from this Trojan horse version of the
   source code. The level of access would be that of the user who
   compiled the source code.

   It is important to understand that the compromise is to the system
   that is used to build the Sendmail software and not to the systems
   that run the Sendmail daemon. Because the compromised system creates a
   tunnel to the intruder-controlled system, the intruder may have a path
   through network access controls.

III. Solution

Obtain an authentic version Sendmail

   The primary distribution site for Sendmail is

          http://www.sendmail.org/

   Sites that mirror the Sendmail source code are encouraged to verify
   the integrity of their sources.

Verify software authenticity

   We strongly encourage sites that recently downloaded a copy of the
   Sendmail distribution to verify the authenticity of their
   distribution, regardless of where it was obtained. Furthermore, we
   encourage users to inspect any and all software that may have been
   downloaded from the compromised site. Note that it is not sufficient
   to rely on the timestamps or sizes of the file when trying to
   determine whether or not you have a copy of the Trojan horse version.

Verify PGP signatures

   The Sendmail source distribution is cryptographically signed with the
   following PGP key:

     pub 1024R/678C0A03 2001-12-18 Sendmail Signing Key/2002
     <sendmailSendmail.ORG>
     Key fingerprint = 7B 02 F4 AA FC C0 22 DA 47 3E 2A 9A 9B 35 22 45

   The Trojan horse copy did not include an updated PGP signature, so
   attempts to verify its integrity would have failed. The sendmail.org
   staff has verified that the Trojan horse copies did indeed fail PGP
   signature checks.

Verify MD5 checksums

   In the absence of PGP, you can use the following MD5 checksums to
   verify the integrity of your Sendmail source code distribution:
   Correct versions:

     73e18ea78b2386b774963c8472cbd309 sendmail.8.12.6.tar.gz
     cebe3fa43731b315908f44889d9d2137 sendmail.8.12.6.tar.Z
     8b9c78122044f4e4744fc447eeafef34 sendmail.8.12.6.tar.sig

   As a matter of good security practice, the CERT/CC encourages users to
   verify, whenever possible, the integrity of downloaded software. For
   more information, see

          http://www.cert.org/incident_notes/IN-2001-06.html

Employ egress filtering

   Egress filtering manages the flow of traffic as it leaves a network
   under your administrative control.

   In the case of the Trojan horse Sendmail distribution, employing
   egress filtering can help prevent systems on your network from
   connecting to the remote intruder-controlled system. Blocking outbound
   TCP connections to port 6667 from your network reduces the risk of
   internal compromised machines communicating with the remote system.

Build software as an unprivileged user

   Sites are encouraged to build software from source code as an
   unprivileged, non-root user on the system. This can lessen the
   immediate impact of Trojan horse software. Compiling software that
   contains Trojan horses as the root user results in a compromise that
   is much more difficult to reliably recover from than if the Trojan
   horse is executed as a normal, unprivileged user on the system.

Recovering from a system compromise

   If you believe a system under your administrative control has been
   compromised, please follow the steps outlined in

          Steps for Recovering from a UNIX or NT System Compromise

Reporting

   The CERT/CC is interested in receiving reports of this activity. If
   machines under your administrative control are compromised, please
   send mail to certcert.org with the following text included in the
   subject line: "[CERT#33376]".

Appendix A. - Vendor Information

   This appendix contains information provided by vendors for this
   advisory. As vendors report new information to the CERT/CC, we will
   update this section and note the changes in our revision history. If a
   particular vendor is not listed below, we have not received their
   comments.
     _________________________________________________________________

   The CERT Coordination Center thanks the staff at the Sendmail
   Consortium for bringing this issue to our attention.
     _________________________________________________________________

   Feedback can be directed to the authors: Chad Dougherty, Marty
   Lindner.
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2002-28.html
   ______________________________________________________________________

CERT/CC Contact Information

   Email: certcert.org
          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
          Postal address:
          CERT Coordination Center
          Software Engineering Institute
          Carnegie Mellon University
          Pittsburgh PA 15213-3890
          U.S.A.

   CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
   EDT(GMT-4) Monday through Friday; they are on call for emergencies
   during other hours, on U.S. holidays, and on weekends.

Using encryption

   We strongly urge you to encrypt sensitive information sent by email.
   Our public PGP key is available from
   http://www.cert.org/CERT_PGP.key

   If you prefer to use DES, please call the CERT hotline for more
   information.

Getting security information

   CERT publications and other security information are available from
   our web site
   http://www.cert.org/

   To subscribe to the CERT mailing list for advisories and bulletins,
   send email to majordomocert.org. Please include in the body of your
   message

   subscribe cert-advisory

   * "CERT" and "CERT Coordination Center" are registered in the U.S.
   Patent and Trademark Office.
   ______________________________________________________________________

   NO WARRANTY
   Any material furnished by Carnegie Mellon University and the Software
   Engineering Institute is furnished on an "as is" basis. Carnegie
   Mellon University makes no warranties of any kind, either expressed or
   implied as to any matter including, but not limited to, warranty of
   fitness for a particular purpose or merchantability, exclusivity or
   results obtained from use of the material. Carnegie Mellon University
   does not make any warranty of any kind with respect to freedom from
   patent, trademark, or copyright infringement.
     _________________________________________________________________

   Conditions for use, disclaimers, and sponsorship information

   Copyright 2002 Carnegie Mellon University.

   Revision History
October 08, 2002: Initial release

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