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AUSCERT External Security Bulletin Redistribution
ESB-2002.381 -- CERT Advisory CA-2002-24
Trojan Horse OpenSSH Distribution
2 August 2002
AusCERT Security Bulletin Summary
Impact: Increased Privileges
Access Required: Remote
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CERT Advisory CA-2002-24 Trojan Horse OpenSSH Distribution
Original issue date: August 1, 2002
Last revised: --
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 OpenSSH package were modified by an intruder and contain
a Trojan horse.
We strongly encourage sites which employ, redistribute, or mirror the
OpenSSH package to immediately verify the integrity of their
The CERT/CC has received confirmation that some copies of the source
code for the OpenSSH package have been modified by an intruder and
contain a Trojan horse. The following advisory has been released by
the OpenSSH development team
The following files were modified to include the malicious code:
These files appear to have been placed on the FTP server which hosts
ftp.openssh.com and ftp.openbsd.org on the 30th or 31st of July, 2002.
The OpenSSH development team replaced the Trojan horse copies with the
original, uncompromised versions at 13:00 UTC, August 1st, 2002. The
Trojan horse copy of the source code was available long enough for
copies to propagate to sites that mirror the OpenSSH site.
The Trojan horse versions of OpenSSH contain malicious code that is
run when the software is compiled. This code connects to a fixed
remote server on 6667/tcp. It can then open a shell running as the
user who compiled OpenSSH.
An intruder operating from (or able to impersonate) the remote address
specified in the malicious code can gain unauthorized remote access to
any host which compiled a version of OpenSSH from this Trojan horse
version of the source code. The level of access would be that of the
user who compiled the source code.
We encourage sites who downloaded a copy of the OpenSSH 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.
Where to get OpenSSH
The primary distribution site for OpenSSH is
Sites that mirror the OpenSSH source code are encouraged to verify the
integrity of their sources.
Verify MD5 checksums
You can use the following MD5 checksums to verify the integrity of
your OpenSSH source code distribution:
At least one version of the modified Trojan horse distributions was
reported to have the following checksum:
Trojan horse version:
Verify PGP signature
Additionally, distributions of the portable release of OpenSSH are
distributed with detached PGP signatures. Note that the Trojan horse
versions were not signed correctly, and attempts to verify the
signatures would have failed.
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
Conectiva Linux distributes openssh-3.4p1 as a security update. The
distributed copy is the original one and is not affected by this
trojan. The detached digital signature is always checked before
building third party packages.
MandrakeSoft has verified that the openssh-3.4p1 sources used to
build it's latest updates (ref. MDKSA-2002:040-1) do not contain
Feedback can be directed to the author: Chad Dougherty.
This document is available from:
CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
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.
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
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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
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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.
August 1, 2002: Initial release
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