When configured to allow password-based or challenge-response authentication, sshd (the OpenSSH server) will use PAM to verify the user's password. Under certain conditions, sshd would reject an invalid authentication attempt without attempting authentication using PAM. If PAM is configured with its default failure delay, the amount of time sshd would take to reject an invalid authentication request would vary widely enough that the timing variations could be used to deduce whether or not an account with a specified name existed on the server. This information could be used to narrow the focus of an attack against some other component of the system. Unmodified versions of OpenSSH versions prior to 3.6.1p1 are vulnerable to this issue. Updates RHSA-2003:224 will contain backported fixes which cause sshd to always attempt PAM authentication when performing password and challenge-response authentication for clients.
An errata has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2003-224.html