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14/11/02, CERT Advisory CA-2002-30 Trojan Horse tcpdump and libpcap Distributions
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Subject: CERT Advisory CA-2002-30 Trojan Horse tcpdump and libpcap Distributions
From: CERT Advisory <>
Date: Wed, 13 Nov 2002 15:17:20 -0500
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Organization: CERT(R) Coordination Center - +1 412-268-7090


CERT Advisory CA-2002-30 Trojan Horse tcpdump and libpcap Distributions

   Original issue date: November 13, 2002
   Last revised: --
   Source: CERT/CC

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


   The  CERT/CC  has received reports that several of the released source
   code  distributions  of the libpcap and tcpdump packages were modified
   by an intruder and contain a Trojan horse.

   We  strongly  encourage  sites  that  use, redistribute, or mirror the
   libpcap  or  tcpdump  packages  to immediately verify the integrity of
   their distribution.

I. Description

   The  CERT/CC  has received reports that some copies of the source code
   for  libpcap,  a  packet  acquisition  library, and tcpdump, a network
   sniffer, have been modified by an intruder and contain a Trojan horse.

   The  following  distributions  were  modified to include the malicious


       md5sum 3a1c2dd3471486f9c7df87029bf2f1e9 tcpdump-3.6.2.tar.gz
       md5sum 3c410d8434e63fb3931fe77328e4dd88 tcpdump-3.7.1.tar.gz


       md5sum 73ba7af963aff7c9e23fa1308a793dca libpcap-0.7.1.tar.gz

   These  modified  distributions  began  to appear in downloads from the
   HTTP server on or around Nov 11 2002 10:14:00 GMT. The
   tcpdump  development  team  disabled  download  of  the  distributions
   containing  the Trojan horse on Nov 13 2002 15:05:19 GMT. However, the
   availability  of  these distributions from mirror sites is unknown. At
   this  time,  it  does not appear that related projects such as WinPcap
   and WinDump contain this Trojan horse.

   The  Trojan  horse  version  of  the  tcpdump source code distribution
   contains  malicious  code  that  is run when the software is compiled.
   This code, executed from the tcpdump configure script, will attempt to
   connect  (via wget, lynx, or fetch) to port 80/tcp on a fixed hostname
   in  order  to  download  a  shell script named services. In turn, this
   downloaded  shell script is executed to generate a C file (conftes.c),
   which is subsequently compiled and run.

   When  executed,  conftes.c  makes an outbound connection to a fixed IP
   address  (corresponding  to  the  fixed hostname used in the configure
   script)  on  port  1963/tcp  and  reads  a single byte. Three possible
   values for this downloaded byte are checked, each causing conftes.c to
   respond in different ways:

     * 'A' will cause the Trojan horse to exit

     * 'D'  will  cause  the  Trojan  to  fork itself, spawn a shell, and
       redirect  this  shell  to  the  connected  IP  address  (Note that
       communication  to  and from this shell is obfuscated by XORing all
       bytes with the constant 0x89.)

     * 'M'  will cause the Trojan horse to close the connection and sleep
       for 3600 seconds

   To  mask  the  activity  of this Trojan horse in tcpdump, libpcap, the
   underlying  packet-capture  library  of  tcpdump,  has  been  modified
   (gencode.c) to explicitly ignore all traffic on port 1963 (i.e., a BPF
   expression of "not port 1963").

II. Impact

   An intruder operating from (or able to impersonate) the remote address
   specified  in the malicious code could gain unauthorized remote access
   to any host that compiled a version of tcpdump with this Trojan horse.
   The  privilege level under which this malicious code would be executed
   would be that of the user who compiled the source code.

III. Solution

   We   encourage   sites   using  libpcap  and  tcpdump  to  verify  the
   authenticity  of  their  distribution,  regardless  of  where  it  was

   Where to get libpcap and tcpdump

   While the compromise of these distributions is being investigated, the
   tcpdump   and   libpcap  maintainers  recommend  using  the  following
   distribution sites:

   Sites  that  mirror  the  source  code  are  encouraged  to verify the
   integrity of their sources. We also encourage users to inspect any and
   all  other 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.

   Verifying checksums

   The MD5 hashes of the vendor suggested updates for libpcap and tcpdump
   are as follows:


       md5sum 03e5eac68c65b7e6ce8da03b0b0b225e tcpdump-3.7.1.tar.gz


       md5sum 0597c23e3496a5c108097b2a0f1bd0c7 libpcap-0.7.1.tar.gz

   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

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


     We  have  checked all our released libpcap and tcpdump packages and
     confirmed that they do not contain the trojan code.


     Problematic  packages  are  only  distributed in Debian/unstable. I
     have  examined  both  source  packages and they did not contain the
     trojan  code  the  HLUG  reported on their web page. Hence, I guess
     that Debian distributes safe source.

MontaVista Software, Inc.

     We  have  examined  our  sources, and our software does not contain
     this trojan. We are not vulnerable to this advisory.


     SuSE Linux products are not vulnerable.

   Feedback can be directed to the author: Roman Danyliw, Chad Dougherty.

   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

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

Getting security information

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   our web site

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   *  "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
     November 13, 2002: Initial release

Version: PGP 6.5.8


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