__________________________________________________________ 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 SOFTWARE: 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. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/n-014.shtml ORIGINAL BULLETIN: http://www.cert.org/advisories/CA-2002-30.html ADDITIONAL The Houston Linux Users Group INFORMATION: http://hlug.fscker.com ______________________________________________________________________________ [***** 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. Overview 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: tcpdump md5sum 3a1c2dd3471486f9c7df87029bf2f1e9 tcpdump-3.6.2.tar.gz md5sum 3c410d8434e63fb3931fe77328e4dd88 tcpdump-3.7.1.tar.gz libpcap md5sum 73ba7af963aff7c9e23fa1308a793dca libpcap-0.7.1.tar.gz These modified distributions began to appear in downloads from the HTTP server www.tcpdump.org 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 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: http://sourceforge.net/projects/tcpdump/ http://sourceforge.net/projects/libpcap/ 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: tcpdump md5sum 03e5eac68c65b7e6ce8da03b0b0b225e tcpdump-3.7.1.tar.gz libpcap 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 http://www.cert.org/incident_notes/IN-2001-06.html 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. Conectiva We have checked all our released libpcap and tcpdump packages and confirmed that they do not contain the trojan code. Debian 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 SuSE Linux products are not vulnerable. Feedback can be directed to the author: Roman Danyliw, Chad Dougherty. This document is available from: http://www.cert.org/advisories/CA-2002-30.html CERT/CC Contact Information Email: cert@cert.org 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 U.S.A. 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 http://www.cert.org/CERT_PGP.key 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 web site http://www.cert.org/ To subscribe to the CERT mailing list for advisories and bulletins, send email to majordomo@cert.org. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. NO WARRANTY 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. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) N-005: Apache 1.3.27 HTTP Server Release N-006: HP pam_authz in LDAP-UX Integration Vulnerabilities N-007: Microsoft Outlook Express Unchecked Buffer in S/MIME Vulnerability N-008: Microsoft Elevation of Privilege in SQL Server Web Tasks N-009: MIT krb5 Buffer Overflow in kadmind4 CIACTech03-001: Spamming using the Windows Messenger Service N-010: Web-Based Enterprise Management on Solaris 8 Installs Insecure Files N-011: Cumulative Patch for Internet Information Service N-012: Windows 2000 Default Permissions Could Allow Trojan Horse Program N-013: ISC Remote Vulnerabilities in BIND4 and BIND8