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| 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. |
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Credit:
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 .
The original advisory can be found at:
http://www.rapid7.com/advisories/R7-0009.txt
The information has been provided by Rapid 7 Security Advisories.
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Vulnerable systems:
* 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
Immune systems:
* 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
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.
Solution:
No solutions available yet.
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 "Immune systems" 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.
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