This information was previously discovered and announced by Dennis
Lubert (plasmahhinformatik.uni-bremen.de).

see http://archives.neohapsis.com/archives/bugtraq/2003-03/0227.html for
original advisory.

Marc Lafortune wrote:
> ========================================================================
=====
>
> ConnecTalk Inc. Security Advisory
>
> Topic: Qpopper leaks information during authentication
>
> Vendor: Eudora
> Product: qpopper 4.0.4 and qpopper 4.0.5
> Note: other versions have not been tested.
> Problem found: May 14, 2003
> Vendor notification: May 14, 2003
> Second vendor notification: May 21, 2003
> Public notification: June 18, 2003
>
> I. Background
>
> Qpopper is the most widely-used server for the POP3 protocol (this
> allows users to access their mail using any POP3 client). Qpopper
> supports the latest standards, and includes a large number of optional
> features. Qpopper is normally used with standard UNIX mail transfer and
> delivery agents such as sendmail or smail.
>
> II. Problem Description
>
> When Qpopper is in the authentication phase, using plain text passwords,
> the response to the PASS command differs depending on the existance of
> the USER. If a valid username and a wrong password are given, Qpopper
> returns a negative reponse and waits for one more command before closing
> the connection. If an invalid username and password are given, Qpopper
> returns a negative response and disconnects right away.
>
> III. Impact
>
> A remote attacker can use this information leak to validate the
> existance of a user account.
>
>

--
Marc Lafortune
Intégrateur / Integrator
ConnecTalk Inc.
http://www.connectalk.com
tel: 514.856.3060

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