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Date: Fri, 28 Mar 2014 18:13:49 +0000
From: Florent Daigniere <>
Subject: Re: CVE request: MediaWiki 1.22.5 login csrf

On Fri, 2014-03-28 at 10:25 -0700, Chris Steipp wrote:
> On Fri, Mar 28, 2014 at 8:56 AM, Florent Daigniere <
>> wrote:
> > On Fri, 2014-03-28 at 08:33 -0700, Chris Steipp wrote:
> > > On Mar 28, 2014 7:54 AM, "Florent Daigniere" <
> > >> 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.

Well, it's not because mistakes were made in the past that we should use
them to justify perpetrating them.

Why do you call that a vulnerability again?

The attacker forfeits his credentials; the target ends up logged in as
the attacker with a session the attacker has no control over... and the
user is made aware (through the UI) that he's logged in as someone else.

No trust boundary breached -> no vulnerability.

After "forced logouts" welcome "forced logins" ;)

> >
> > > 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.

If mediawiki really allows users to define javascript that will be
loaded on pages they visit, that's a vulnerability... There's no way to
do that securely if the "content" and "application" data are served from
the same FQDN.


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