__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Vulnerabilities in SSH2 Implementations from Multiple Vendors [Rapid 7, Inc. Security Advisory, R7-0009] December 17, 2002 19:00 GMT Number N-028 ______________________________________________________________________________ PROBLEM: SSH servers and clients from several vendors contain vulnerabilities that may allow denial-of-service attacks and/or arbitrary code execution. The vulnerabilities occur before user authentication takes place. AFFECTED Multiple vendor versions of SSH software may be affected. SOFTWARE: DAMAGE: A remote attacker could potentially gain root privileges and execute arbitrary code. SOLUTION: Check with your vendor for platform-specific solutions. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. There are no known exploits at this time. ASSESSMENT: ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/n-028.shtml ORIGINAL BULLETIN: http://www.rapid7.com/advisories/R7-0009.txt Monitor Rapid 7 Advisory for vendor updates. ______________________________________________________________________________ [***** Start Rapid 7, Inc. Security Advisory, R7-0009 *****] -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 _______________________________________________________________________ Rapid 7, Inc. Security Advisory Visit http://www.rapid7.com/ to download NeXpose(tm), our advanced vulnerability scanner. Linux and Windows 2000 versions are available now! _______________________________________________________________________ Rapid 7 Advisory R7-0009 Vulnerabilities in SSH2 Implementations from Multiple Vendors Published: December 16, 2002 Revision: 1.0 http://www.rapid7.com/advisories/R7-0009.txt CERT: CA-2002-36 http://www.cert.org/advisories/CA-2002-36.html CVE: Multiple CVE CANs assigned: - CAN-2002-1357 (incorrect length) - CAN-2002-1358 (lists with empty elements/empty strings) - CAN-2002-1359 (large packets and large fields) - CAN-2002-1360 (string fields with zeros) 1. Affected system(s): KNOWN VULNERABLE: - F-Secure Corp. SSH servers and clients for UNIX v3.1.0 (build 11) and earlier - F-Secure Corp. SSH for Windows v5.2 and earlier - SSH Communications Security, Inc. SSH for Windows v3.2.2 and earlier - SSH Communications Security, Inc. SSH for UNIX v3.2.2 and earlier - FiSSH SSH client for Windows v1.0A and earlier - InterSoft Int'l, Inc. SecureNetTerm client for Windows v5.4.1 and earlier - NetComposite ShellGuard SSH client for Windows v3.4.6 and earlier - Pragma Systems, Inc. SecureShell SSH server for Windows v2 and earlier - PuTTY SSH client for Windows v0.53 and earlier (v0.53b not affected) WinSCP SCP client for Windows v2.0.0 and earlier APPARENTLY NOT VULNERABLE: - BitVise WinSSHD server for Windows v3.05 - LSH v1.5 - OpenSSH v3.5 and earlier - TTSSH SSH Extension for TeraTerm Pro - VanDyke SecureCRT client v3.4.3 for Windows - VanDyke VShell server v1.2 for Windows UNKNOWN / NOT TESTED: - MacSSH - SSHv1 implementations (see {1}) - SSHv2 enabled network appliances 2. Summary SSH servers and clients from several vendors contain vulnerabilities that may allow denial-of-service attacks and/or arbitrary code execution. The vulnerabilities arise from various deficiencies in the greeting and key-exchange-initialization phases of the SSHv2 transport layer. 3. Vendor status and information F-Secure Corporation http://www.f-secure.com Vendor has been notified. Release information is unknown at this time. F-Secure has characterized this issue as not exploitable. FiSSH http://pgpdist.mit.edu/FiSSH/index.html Vendor has been notified. Release information is unknown at this time. NetComposite (ShellGuard) http://www.shellguard.com Vendor has been notified. Release information is unknown at this time. Pragma Systems, Inc. http://www.pragmasys.com Vendor has been notified. The fixed version is SecureShell v3.0, which was released on November 25 2002. PuTTY http://www.chiark.greenend.org.uk/~sgtatham/putty/ Vendor has been notified. The fixed version is PuTTY v0.53b, which was released on November 12, 2002. SSH Communications Security, Inc. http://www.ssh.com Vendor has been notified. Release information is unknown at this time. SSH, Inc. has characterized this issue as not exploitable. SecureNetTerm (InterSoft International, Inc.) http://www.securenetterm.com Vendor notified. The fixed version is SecureNetTerm v5.4.2, released on November 14 2002. WinSCP2 http://winscp.vse.cz/eng/ Vendor has been notified. Release information is unknown at this time. 4. Solution No solutions available yet. 5. Detailed analysis To study the correctness and security of SSH server and client implementations {2}, the security research team at Rapid 7, Inc. has designed the SSHredder SSH protocol test suite containing hundreds of sample SSH packets. These invalid and/or atypical SSH packets focus on the greeting and KEXINIT (key exchange initialization) phases of SSH connections. We then applied the SSHredder suite to some popular SSH servers and clients, observing their behavior when presented with a range of different input. Several implementation errors were discovered, most of which involve memory access violations. While the impact is different for each product tested, some of these errors were easily exploitable, allowing the attacker to overwrite the stack pointer with arbitrary data. In most cases, only the most current versions of the applications were tested. Vendors listed as "Apparently NOT VULNERABLE" are encouraged to run the tests against older versions of their applications. The SSHredder test suite is now available for download from Rapid 7's web site ( http://www.rapid7.com ). A pre-release version of SSHredder was provided to SSH vendors for testing prior to public disclosure. SSHredder has been released under the BSD license. The test cases combine several test groups of similarly structured data: - Invalid and/or incorrect SSH packet lengths (including zero, very small positive, very large positive, and negative). - Invalid and/or incorrect string lengths. These were applied to the greeting line(s), plus all the SSH strings in the KEXINIT packets). - Invalid and/or incorrect SSH padding and padding lengths. - Invalid and/or incorrect strings, including embedded ASCII NULs, embedded percent format specifiers, very short, and very long strings. This test group was applied to the greeting line(s), plus all the SSH strings in the KEXINIT packets). - Invalid algorithm lists. In addition to the existing string tests, invalid encryption, compression, and MAC algorithm names were used, including invalid algorithm domain qualifiers; invalid algorithm lists were created by manipulating the separating commas. The individual tests in each group were combined systematically to produce a test suite of 666 packets. A full permutation of every test in each test group would have yielded a test suite that is too large to distribute, so a representative sample of packets was chosen from each group. Please note that greeting and KEXINIT are only the first and second phases of SSH connections. A full test suite for every SSH protocol message could potentially reveal other latent vulnerabilities. 6. Notes [1] While SSHv1 has no KEXINIT phase, many of these test cases could affect both SSHv1 and SSHv2 in a generic way). SSHv1 implementations were not tested. [2] The SSH protocol is described in several IETF drafts, which can be found at http://www.ietf.org/ids.by.wg/secsh.html . 7. Contact Information Rapid 7 Security Advisories Email: advisory@rapid7.com Web: http://www.rapid7.com/ Phone: +1 (212) 558-8700 8. Disclaimer and Copyright Rapid 7, Inc. is not responsible for the misuse of the information provided in our security advisories. These advisories are a service to the professional security community. There are NO WARRANTIES with regard to this information. Any application or distribution of this information constitutes acceptance AS IS, at the user's own risk. This information is subject to change without notice. This advisory Copyright (C) 2002 Rapid 7, Inc. Permission is hereby granted to redistribute this advisory, providing that no changes are made and that the copyright notices and disclaimers remain intact. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (OpenBSD) iD8DBQE9/a5kcL76DCfug6wRAoIdAJ0Xg1HUeXQk5aNzBaKVcS4XP9rlpACguQk6 G2ihG+Zr3V/VE/1C21p4yf4= =iqCp -----END PGP SIGNATURE----- [***** End Rapid 7, Inc. Security Advisory, R7-0009 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Rapid 7, Inc. 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. 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