[WEB SECURITY] How are you tackling CSRF?

Thomas Ptacek thomas at matasano.com
Sat Apr 23 18:10:02 EDT 2011


He's not talking about referrer headers; he's talking about subsetting the inventory of forms down to those that actually require CSRF protection.

On Apr 23, 2011, at 4:23 PM, James Manico wrote:

> Hey Steve,
> 
> In a intranet environment where all browser/network settings are
> controlled, HTTP Referrer header verification (what you are suggesting
> below) can be effective as a •partial• CSRF defense to be used in
> addition to cryptographic nonces.
> 
> But when your website has Internet-facing customers/consumers, you can
> no longer rely on referrer headers. Some organizations strip them in
> an outbound way to prevent data leakage.
> 
> Jim Manico
> 
> On Apr 23, 2011, at 9:33 AM, "Steven M. Christey"
> <coley at rcf-smtp.mitre.org> wrote:
> 
>> 
>> Disclaimer: I'm mostly ignorant about automated detection of CSRF.
>> 
>> Just a random thought.  Has anybody investigated filtering/prioritizing forms based on how many pages invoke those forms?  I would guess that some critical state-changing forms would only be accessible from a single page, whereas (e.g.) a search or login function might be accessible from many.
>> 
>> In a CMS scenario for example, there might be lots of pages that link to a "create a new page" form, but only one page that points to the form "commit the new page content you just filled in."
>> 
>> This might not serve as *proof* that a form should have CSRF protection, but it might be one way of sorting the potential false-positives.
>> 
>> - Steve
>> 
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Thomas Ptacek // matasano security // founder, product manager
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