Two weaknesses have been reported in OpenSSH, which can be exploited by malicious users and malicious people to disclose potentially sensitive information.

1) OpenSSH does not properly initialise a nonce field with random data when generating legacy certificates ("-t" command line option of ssh-keygen). This can result in certain stack memory being used as nonce, which can lead to the disclosure of potentially sensitive information.

Note: Certificates with user-specified contents may also be less protected against hash collision attacks. However, these attacks are currently not considered practical for the SHA signatures used.

This weakness is reported in versions 5.6 and 5.7.

2) An error within the "auth_parse_options()" function (auth-options.c) can be exploited to e.g. disclose the forced commands configured in the authorized_keys file.

This weakness is reported in versions prior to 5.7-p1.

Solution
Update to version 5.8. Rotate the CA key for legacy certificates generated with a vulnerable version. Weakness #2 is also fixed in version 5.7-p1.

Provided and/or discovered by
1) The vendor credits Mateusz Kocielski.
2) Disclosed in a CVS commit.

Changelog
Further details available to Secunia VIM customers

Original Advisory
OpenSSH:
http://www.openssh.com/txt/legacy-cert.adv
http://www.openssh.com/txt/release-5.8
http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/auth-options.c.diff?r1=1.53;r2=1.54

Deep Links
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