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The U.S. Department of Energy
Computer Incident Advisory Capability
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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.
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VULNERABILITY The risk is MEDIUM. There are no known exploits at this time.
ASSESSMENT:
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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.
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_______________________________________________________________________
Rapid 7, Inc. Security Advisory
Visit http://www.rapid7.com/ to download NeXpose(tm), our
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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.
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[***** 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
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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
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