I need to read more about this, but I am interested to know if there are any 
advantages to storing the token in a cookie for validation rather than putting 
it into the session. I suppose if statelessness is required then it is 
necessary. One advantage to storing it in session is that it does help prevent 
the double form submit error. See 
http://www.nabble.com/Double-submit-problem-td15957979.html#a15957979 for 
example.

The JIRA issue you mention has a broken link. It looks like it should be 

http://freedom-to-tinker.com/blog/wzeller/popular-websites-vulnerable-cross-site-request-forgery-attacks

If I am not mistaken.

-----Original Message-----
From: Jörn Zaefferer [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, October 22, 2008 8:05 AM
To: users@wicket.apache.org
Subject: Re: CSRF Protection: double submitted cookie

I've created a ticket and attached a reference implementation:
https://issues.apache.org/jira/browse/WICKET-1885

Jörn

On Mon, Oct 20, 2008 at 11:31 PM, Jörn Zaefferer
<[EMAIL PROTECTED]> wrote:
> The double-submitted-cookie isn't related to double submit protection,
> no. Thats a completely different turf.
>
> With that out of the way, its enough to create just one cookie and use
> that both while rendering and validating forms.
>
> I hope that makes it clearer. I'll try to provide a reference
> implementation tomorrow.
>
> Jörn
>
> On Mon, Oct 20, 2008 at 12:58 PM, Johan Compagner <[EMAIL PROTECTED]> wrote:
>> hmm i will read the paper then
>> I stil dont get it how it is possible with 1 cookie, that then can never
>> change when it is first generated
>> and all the forms also just have that value right?
>>
>> But it is also for double submit protection right? So the cookie has to
>> change right?
>> But how can you then have 1 cookie? for all the forms?
>> If i submit one and that is rerendered or redirected to another page.
>> (so it has a new cookie so the double submit cant happen)
>> But if a new cookie is set then all other forms are also suddenly invalid..
>> and that looks pretty wrong to me
>>
>> johan
>>
>>
>> On Mon, Oct 20, 2008 at 12:44 PM, Jörn Zaefferer <
>> [EMAIL PROTECTED]> wrote:
>>
>>> No, the cookie is subject to the same-origin-policy, both in reading
>>> and writing. The request is authenticated because the session cookie
>>> is set, but its invalid when the form itself is missing the value.
>>> Combining the attack with XSS would give access to the cookie, but
>>> then he could just as well hijack the session directly.
>>>
>>> In other words: With CSRF alone there is no way for the attacker to
>>> read the cookie, therefore its enough to use just one.
>>>
>>> Their whitepaper may do a better job of explaining the techniquie:
>>> http://www.freedom-to-tinker.com/sites/default/files/csrf.pdf
>>> Solutions are described on page 8ff.
>>>
>>> Jörn
>>>
>>> On Mon, Oct 20, 2008 at 12:33 PM, Johan Compagner <[EMAIL PROTECTED]>
>>> wrote:
>>> > what i dont get
>>> > if an attacker wants to submit the form. and it can get to the form it
>>> can
>>> > do the post
>>> > but you say it cant access the cookie. But if the cookie value is just
>>> > compared to the form post value
>>> > we have to make sure that the name of the cookie cant be guessed right?
>>> So
>>> > what should the name be?
>>> >
>>> > Because if the name would be "wicket-form-uuid" then couldnt the attacker
>>> > also just generate that cookie?
>>> >
>>> > I guess there is a cookie per form (there can be many forms on the same
>>> page
>>> > or different active pages)
>>> > and that cookie must be regenerated/set on every form render?
>>> >
>>> > johan
>>> >
>>> >
>>> > On Mon, Oct 20, 2008 at 11:27 AM, Jörn Zaefferer <
>>> > [EMAIL PROTECTED]> wrote:
>>> >
>>> >> Hi,
>>> >>
>>> >> my application currently uses CryptedUrlWebRequestCodingStrategy to
>>> >> protect against CRSF attacks. Afaik 1.3.5 will include an update that
>>> >> generates the key based on user sessions:
>>> >> http://issues.apache.org/jira/browse/WICKET-1782
>>> >> According to Johan Compagner, there are still issues with that
>>> >> approach, though I don't know if that has been fixed:
>>> >> http://www.nabble.com/Wicket-not-secure--to19556259.html#a19557593
>>> >>
>>> >> Anyway, the point of this mail is to bring up a different strategy for
>>> >> CSRF protection, the double-submitted-cookie. Discussion of that are
>>> >> here http://www.codinghorror.com/blog/archives/001175.html which links
>>> >> to this article, including a whitepaper:
>>> >>
>>> >>
>>> http://freedom-to-tinker.com/blog/wzeller/popular-websites-vulnerable-cross-site-request-forgery-attacks
>>> >>
>>> >> The basic idea is:
>>> >>
>>> >> "When a user visits a site, the site should generate a
>>> >> (cryptographically strong) pseudorandom value and set it as a cookie
>>> >> on the user's machine. The site should require every form submission
>>> >> to include this pseudorandom value as a form value and also as a
>>> >> cookie value. When a POST request is sent to the site, the request
>>> >> should only be considered valid if the form value and the cookie value
>>> >> are the same. When an attacker submits a form on behalf of a user, he
>>> >> can only modify the values of the form. An attacker cannot read any
>>> >> data sent from the server or modify cookie values, per the same-origin
>>> >> policy. This means that while an attacker can send any value he wants
>>> >> with the form, he will be unable to modify or read the value stored in
>>> >> the cookie. Since the cookie value and the form value must be the
>>> >> same, the attacker will be unable to successfully submit a form unless
>>> >> he is able to guess the pseudorandom value."
>>> >>
>>> >> For Wicket, this would mean: Generate a pseudorandom value and set is
>>> >> as a session cookie, when the cookie doesn't yet exist. Insert a
>>> >> hidden input into each form with the generated value. Validate that
>>> >> the value equals the cookie when submitting a form. The input and
>>> >> validation can be abstracted into a Form subclass (or even add it to
>>> >> Wicket's Form class...).
>>> >>
>>> >> That really easy to implement, is much more efficient (generate only
>>> >> one value per user/browser session, store it on the client, not the
>>> >> server) and is now the most common strategy to protect against CSRF
>>> >> attacks. I've read a lot about CSRF, and this strategy seems the only
>>> >> one both easy enough to implement and without holes.
>>> >>
>>> >> What do you think? Should Wicket support that out-of-the-box?
>>> >>
>>> >> Jörn
>>> >>
>>> >
>>>
>>
>

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