What about instances where an identity framework is used, such as CA's
Siteminder or IBM's Identity Mangament Suite? Closing the browser will
result in the session begin invalidated - I'm not sure if that cascades to
releasing other resources or not.

On Wed, 3 May 2006, Auri Rahimzadeh wrote:

> In addition, having the session state continues to reserves those resources
> on the server. So, if there were open recordsets in memory (bad developer!),
> login information, database connections, they all stay there. All closing
> the window does (and this assumes you have closed *all* browser windows, not
> just the one window that was being used), is tell the browser to destroy the
> cookie on the client. This is my no means secure, as has been pointed out by
> those questioning "what if the session key is in the querystring", which is
> generally frowned upon due to session hijacking attacks and replay attacks.
>
> The performance issue is very real. Imagine a server with 1000 users logging
> on in 20 minutes (probably an ASP scenario, and assuming the server is set
> up to time out sessions in 20 minutes, which is pretty standard). If each of
> them has 100K of session data (developers usually use it for convenience and
> for variable/data persistence), that's 100,000K (100 megs), used on the
> server. Now 10,000 users? 1 gig... Vertical and horizontal scaling gets
> expensive. In addition, the resources you normally need to release per
> session aren't released, so you could run out of available database pool
> connections, have open hooks on files, and so forth, and basically break
> your app. This only gets worse with servers with even longer session
> timeouts.
>
> I've never had a client *not* want a logoff button in their site specs,
> although they many times forget to ask for one since they're so used to it.
> I ask about putting one in and they usually say "of course!"
>
> Keep in mind that users many times may just close their windows instead of
> logging out. But many *will* logout, just to be safe/sure.
>
> Ahh, yes, another note: Session variables can be the bain of a developer's
> existence, just like cookies. If the wrong data is persisted, and the
> developer assumes a session key or cookie doesn't exist, and reads it
> without first making sure it's not from an old session or invalid data,
> things can get very, very messy (and darn hard to debug).
>
> Thanks again!
>
> Best,
>
> Auri Rahimzadeh
> Author
> Hacking the PSP
> www.hackingpsp.com
>
>
> -----Original Message-----
> From: Rod Divilbiss [mailto:rod (at) rodsdot (dot) com [email concealed]]
> Sent: Tuesday, May 02, 2006 8:40 AM
> To: test.future (at) gmail (dot) com [email concealed]
> Cc: webappsec (at) securityfocus (dot) com [email concealed]
> Subject: RE: Is logoff feature necessary
>
> Closing the browser will cause the session to end. It will however takes
> some amount of time (usually 20 minutes) for the session to be terminated by
> the server. It may be possible for the user to reopen their browser before
> the session times out and reestablish the session. (Depends on how session
> state is maintained and how the web application is written.)
>
> Having a logoff button which explicitly kills the session is not a bad
> thing.
>
> -----Original Message-----
> From: test.future (at) gmail (dot) com [email concealed] [mailto:test.future (at) gmail (dot) com [email concealed]]
> Sent: Tuesday, May 02, 2006 2:41 AM
> To: webappsec (at) securityfocus (dot) com [email concealed]
> Subject: Is logoff feature necessary
>
> We have a web applicaiton which do not have logoff button. The developer
> claims that it is unnecessary, since the session can be terminated by
> closing the browser. Is it correct? Thanks.
>
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