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securityvulnsSecurityvulnsSECURITYVULNS:DOC:3882
HistoryDec 17, 2002 - 12:00 a.m.

R7-0009: Vulnerabilities in SSH2 Implementations from Multiple Vendors

2002-12-1700:00:00
vulners.com
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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!

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: [email protected]
    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: [email protected]
Web: http://www.rapid7.com/
Phone: +1 (212) 558-8700
PGP: http://www.rapid7.com/advisories/R7-PKey2002.txt

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