Re: Concurrent Sessions and User Feedback

From: Daniel Staal <DStaal(at)usa.net>
Date: Sun Apr 06 2003 - 20:15:17 EDT

--On Saturday, April 5, 2003 2:33 PM -0500 Susan Olson <olson.susan@excite.com> wrote:

> My questionÖwhat is the best way to handle ìfeedbackî for users
> attempting to access an account that is already logged-on?
> Currently, users get a message stating that the account that they
> are attempting to use is already logged-on. I am not comfortable
> with this because it lends to the possible harvesting of valid
> UserIDs & Passwords by an ìevil doer.î Also, I have a similar
> issue with the ìfeedbackî given to users when an account is locked

No specific suggestions besides the obvious: change the error messages so that they are all the same. (Something along the line of "This username/password combination in not valid at this time." It is true in all cases...)

The problem of course is debugging. You may want to put in error codes for debugging (though a smart attacker could figure the error codes out and then you are back where you started. Still, it would be useful *before* you deploy at least, and you could remove them at the end of a debug cycle.)

The other problem is if you have an attacker smart enough to check timing differences. If the time to decide one case is detectably different then the other that allows an avenue of opportunity. It may happen that all differences are indistinshable from network latency variations, but you would want to be sure...

Daniel T. Staal

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