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Date: Fri, 28 Mar 2014 10:25:00 -0700
From: Chris Steipp <csteipp@...imedia.org>
To: oss-security@...ts.openwall.com
Subject: Re: CVE request: MediaWiki 1.22.5 login csrf

On Fri, Mar 28, 2014 at 8:56 AM, Florent Daigniere <
florent.daigniere@...stmatta.com> wrote:

> On Fri, 2014-03-28 at 08:33 -0700, Chris Steipp wrote:
> > On Mar 28, 2014 7:54 AM, "Florent Daigniere" <
> > florent.daigniere@...stmatta.com> wrote:
> > >
> > > Sorry to be thick here but it still doesn't make any sense to me...
> > >
> > > The session-id should be renewed upon login AND any
> credential/privilege
> > > change (that includes password changes). This protects against session
> > > fixation attacks (where the attacker coerce a user into using a session
> > > he controls).
> > >
> > > On these pages, there's usually no need for anti-CSRF protection as
> they
> > > tend to require credentials (something the attacker, by definition,
> > > doesn't have).
> >
> > Slightly different attack. The attacker (who knows their own password and
> > chooses the reset-to password) was able to cause a logged out user
> (victim)
> > to login with the attacker's account via the change password form.
> >
>
> That is the textbook example of a session-fixation attack. The "end
> state" is that the victim uses a session the attacker can control.
>

Except that it has very little to do with the user's session. We can (and
do) refresh the user's session id as part of the login process. We could
refresh the user's session every time the user visits that form, and the
PoC on the bug would still work.

The PoC on the bug shows that a non mediawiki domain can make a POST to the
mediawiki domain to login an anonymous user as the attacker.  Using the
definition from owasp, "CSRF is an attack which forces an end user to
execute unwanted actions on a web application in which he/she is currently
authenticated" this satisfies the part that an attacker is taking unwanted
action on behalf of the victim. If you want to argue that "logging in" is
inherently an action by an unauthenticated user and so it doesn't meet they
"in which he/she is currently authenticated" then I'm happy to not call
this CSRF. However we did call the same attack a "login CSRF" for the
nearly identical issue CVE-2010-1150 and a very similar CVE-2012-5394.



>
> > This attack is somewhat specific to mediawiki since we allow users to
> > define JavaScript that will be loaded on pages they visit while logged
> > in... So the victim in this case would run the attacker's personal
> > JavaScript.
> >
>
> It still doesn't make sense. Anti-CSRF tokens are only useful if the
> "malicious script" is not running with the same origin!
>

I think I threw you off here-- this is just one reason why an attacker
might want to do this. It's tangential to the actual flaw we fixed.


>
> Florent
>

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