bugtraq - Re: Circumventing CSFR Form Token Defense

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Date: Wed, 10 Jan 2007 08:38:44 +0100
From: Florian Weimer <fw@...eb.enyo.de>
To: Jim Manico <jim@...ico.net>
Cc: bugtraq@...urityfocus.com
Subject: Re: Circumventing CSFR Form Token Defense

* Jim Manico:

> CONJECTURE: An attacker could write a hybrid "html inspection, CSRF
> attack" mimicking an exact important form (like the funds transfer
> form for an exact bank) **even if the form in question uses form
> tokens**.

I'm not sure what you mean by "form tokens", but correctly generated
tokens are unique to the user's session.

>   a) The javascript makes a simple HTTP/S request to the form it is
>   trying to mimic and inspects the returned HTML for the purpose of
>   pulling out a valid form key since the form key NAME is known from
>   (1).

To work, this requires a cross-site scripting vulnerability in the web
application (or lack of enforcement of the same-origin policy by the
browser).  (The rule of thumb is: XSS for read access, CSRF for write
access.)