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TUCoPS :: Linux :: General :: n-014.txt

Trojan Horse tcpdum and libpcap Distributions (CIAC N-014)


                       The U.S. Department of Energy
                   Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

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

November 13, 2002 21:00 GMT                                       Number N-014
PROBLEM:       Several of the released source code distributions of the
               libpcap and tcpdump packages were modified by an intruder and
               contain a Trojan horse. Early reports state that modified
               versions began appearing around October 30, 2002.
AFFECTED       tcpdump and libpcap
DAMAGE:        Intruders operating from 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.
SOLUTION:      Sites using libpcap and tcpdump are encouraged to verify the
               authenticity of their versions, regardless of where it was
               obtained. See CERT's Advisory for currently trusted
               distribution sites.
VULNERABILITY  The risk is HIGH. Attackers could gain unauthorized remote
ASSESSMENT:    access and execute arbitrary code of attacker's choice.
 ADDITIONAL          The Houston Linux Users Group
[***** Start CERT Advisory CA-2002-30 *****]

CERTŪ 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 code:


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 

'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 obtained. 

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 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 

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 comments. 


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

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 information. 

Getting security information

CERT publications and other security information are available from our 
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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

[***** End CERT Advisory CA-2002-30 *****]

CIAC wishes to acknowledge the contributions of CERT Coordination Center and 
The Houston Linux Users Group for the information contained in this bulletin.

CIAC, the Computer Incident Advisory Capability, is the computer
security incident response team for the U.S. Department of Energy
(DOE) and the emergency backup response team for the National
Institutes of Health (NIH). CIAC is located at the Lawrence Livermore
National Laboratory in Livermore, California. CIAC is also a founding
member of FIRST, the Forum of Incident Response and Security Teams, a
global organization established to foster cooperation and coordination
among computer security teams worldwide.

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can be contacted at:
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