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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
     <sendmail@Sendmail.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  cert@cert.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: cert@cert.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
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   http://www.cert.org/

   To  subscribe  to  the CERT mailing list for advisories and bulletins,
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   *  "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
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     _________________________________________________________________

   Conditions for use, disclaimers, and sponsorship information

   Copyright 2002 Carnegie Mellon University.

   Revision History
October 08, 2002: Initial release

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