CERT® Advisory CA-2002-24 Trojan Horse OpenSSH DistributionOriginal issue date: August 1, 2002
Last revised: August 2, 2002
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 distribution.
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:Correct versions:
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 comments.
Feedback can be directed to the author: Chad Dougherty.
This document is available from: http://www.cert.org/advisories/CA-2002-24.html
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Copyright 2002 Carnegie Mellon University.
August 1, 2002: Initial release August 1, 2002: Added IBM vendor statement August 2, 2002: Added Debian, NetBSD, and Nortel vendor statements