Bug 98594

Summary: CAN-2003-0190 OpenSSH valid username information leak
Product: Red Hat Enterprise Linux 2.1 Reporter: Mark J. Cox <mjc>
Component: opensshAssignee: Nalin Dahyabhai <nalin>
Status: CLOSED ERRATA QA Contact: Brian Brock <bbrock>
Severity: medium Docs Contact:
Priority: medium    
Version: 2.1Keywords: Security
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OS: Linux   
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Last Closed: 2003-07-29 07:27:38 UTC Type: ---
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Description Mark J. Cox 2003-07-04 11:16:21 UTC 
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.
Comment 1 Mark J. Cox 2003-07-29 07:27:38 UTC 
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