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_______________________________________________________________________
                     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!
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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:
               o CAN-2002-1357 (incorrect length)
               o CAN-2002-1358 (lists with empty elements/empty strings)
               o CAN-2002-1359 (large packets and large fields)
               o CAN-2002-1360 (string fields with zeros)

1. Affected system(s):

   KNOWN VULNERABLE:
    o F-Secure Corp. SSH servers and clients for UNIX
       v3.1.0 (build 11) and earlier
    o F-Secure Corp. SSH for Windows
       v5.2 and earlier
    o SSH Communications Security, Inc. SSH for Windows
       v3.2.2 and earlier
    o SSH Communications Security, Inc. SSH for UNIX
       v3.2.2 and earlier
    o FiSSH SSH client for Windows
       v1.0A and earlier
    o InterSoft Int'l, Inc. SecureNetTerm client for Windows
       v5.4.1 and earlier
    o NetComposite ShellGuard SSH client for Windows
       v3.4.6 and earlier
    o Pragma Systems, Inc. SecureShell SSH server for Windows
       v2 and earlier
    o PuTTY SSH client for Windows
       v0.53 and earlier (v0.53b not affected)
    o WinSCP SCP client for Windows
       v2.0.0 and earlier

   APPARENTLY NOT VULNERABLE:
    o BitVise WinSSHD server for Windows v3.05
    o LSH v1.5
    o OpenSSH v3.5 and earlier
    o TTSSH SSH Extension for TeraTerm Pro
    o VanDyke SecureCRT client v3.4.3 for Windows
    o VanDyke VShell server v1.2 for Windows

   UNKNOWN / NOT TESTED:
    o MacSSH
    o SSHv1 implementations (see {1})
    o 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:

      o Invalid and/or incorrect SSH packet lengths (including
        zero, very small positive, very large positive, and
        negative).

      o Invalid and/or incorrect string lengths.  These were applied
        to the greeting line(s), plus all the SSH strings in the
        KEXINIT packets).

      o Invalid and/or incorrect SSH padding and padding lengths.

      o 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).

      o 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.
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==============================
Rapid 7 Security Research Team
Email: advisory@rapid7.com
Web: http://www.rapid7.com/
Phone: +1 (212) 558-8700
PGP: http://www.rapid7.com/advisories/R7-PKey2002.txt
==============================