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TUCoPS :: Linux :: Apps N-Z :: lnx5740.htm

sendmail 8.12.6 Distribution Compromised with trojan
9th Oct 2002 [SBWID-5740]

	sendmail distribution compromised


	sendmail 8.12.6


	 Editor's note :



	Although not a bug per see, this is bad enough to propagate the news.

	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.



	   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:





	   These  files  began  to  appear  in  downloads  from  the  FTP  server  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




	   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


	     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

	   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




	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



	   The  CERT/CC  is  interested in receiving reports of this activity. If

	   machines  under  your  administrative  control are compromised, please

	   send  mail  to  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




	   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




	   This document is available from:



	CERT/CC Contact Information


	          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



	   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


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



	Getting security information

	   CERT  publications  and  other security information are available from

	   our web site


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

	   send  email  to Please include in the body of your



	   subscribe cert-advisory


	   *  "CERT"  and  "CERT  Coordination Center" are registered in the U.S.

	   Patent and Trademark Office.




	   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


	Version: PGP 6.5.8










	see above

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