> I understand I can just override handle_unverified_request to get the
> behavior I want, but I think that the announcement did not highlight
> this enough. Sure, it mentions that the session will be reset, and no
> error will be raised. It also mentions that you should override the
> default if you need to clear more than just the session (remember-me
> functionality). But it doesn't mention that if you want to make sure
> the request isn't processed (old behavior), you need to take extra
> steps, because by default, it will just go through.
CSRF attacks are about using *session* data to perform an action
without the user's knowledge. The attack you're describing here,
which doesn't rely on session data, could also be performed just using
curl from the command line of the attackers laptop, there's no need to
involve the user's computer at all.
If there's no involvement of the session (or some other
client-browser-specific) vector, then it's not a CSRF attack.
However you're correct that we need a little more documentation than
we had previously because the attack vectors are a touch trickier. I
intend to post an FAQ blog post and update the guides in a few days to
ensure that it's crystal clear what's required.
The thing to remember is that we *can't* raise an exception in the
default case any more because *every api request would be rejected*.
For users who don't have any API, then the original behaviour was
probably fine. However a large portion of rails apps do and we can't
completely break them!
> I hope you see my point.
I see your point and agree that we need a little more documentation
around this. However it is nowhere near as simple as your suggestions
imply. Developers will have to understand the implications of their
choices.
I suspect we'll end up with an api like:
protect_from_forgery :on_failure=>:raise
protect_from_forgery :on_failure=>:reset
protect_from_forgery :on_failure=>:some_method
protect_from_forgery :on_failure=> proc { ... }
I realise that the previous situation where you could just ignore the
issue was greatly preferable, but that was based on some assumptions
which don't hold. The old rules don't apply anymore.
> Mathijs
>
>
> On Feb 11, 9:51 pm, Jon Leighton <[email protected]> wrote:
>> Hi there,
>>
>> As you've identified, the difference between 2.3.10 and 2.3.11, and
>> between 3.0.3 and 3.0.4, in how they handle invalid csrf tokens is that
>> the former will raise ActionController::InvalidAuthenticityToken, but
>> the latter will reset the session.
>>
>> What we are trying to protect against is the following situation:
>>
>> * Alice is logged in to Facebook
>> * Alice visits badsite.com
>> * Mallory, who owns badsite.com has added some code into the page which
>> makes a request to facebook.com and posts on Alice's wall.
>> * Alice visits badsite.com and without her intending it to be, a comment
>> is posted on her wall
>>
>> With the current CSRF protection, the following will happen:
>>
>> * Alice is logged in to Facebook
>> * Alice visits badsite.com
>> * Mallory, who owns badsite.com has added some code into the page which
>> makes a request to facebook.com and posts on Alice's wall.
>> * Alice visits badsite.com and without her intending it to be, a request
>> is made to post on her wall
>> * Facebook detects that there is no CSRF token associated with the
>> request, and so logs her out by resetting the session
>> * Then, based on the authorisation rules within the application,
>> Facebook denies to post on the wall, because the user is not logged in
>>
>> With the old CSRF protection, the following will happen:
>>
>> * Alice is logged in to Facebook
>> * Alice visits badsite.com
>> * Mallory, who owns badsite.com has added some code into the page which
>> makes a request to facebook.com and posts on Alice's wall.
>> * Alice visits badsite.com and without her intending it to be, a request
>> is made to post on her wall
>> * Facebook detects that there is no CSRF token associated with the
>> request and so refuses to serve the request in any way (returns 500)
>> * So nothing gets posted on the wall
>>
>> The point is, they are different but both have the effect of preventing
>> the wall post.
>>
>> If for some reason you specifically want an exception to be raised in
>> this situation, you can customise handle_unverified_request, but it
>> doesn't compromise the aim of the CSRF protection to no raise an
>> exception, so long as the request is not allowed to go through as
>> authenticated by the existing session.
>>
>> Jon
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Fri, 2011-02-11 at 11:28 -0800, Mathijs wrote:
>> > Hi all,
>>
>> > I think CSFR protection broke in rails 2.3.11.
>> > As in: it's turned off now.
>>
>> > I tried this in rails 2.3.10 and in 2.3.11 and 2.3.11 seems broken.
>>
>> > >rails csrftest
>> > >cd csrftest
>> > >script/generate scaffold post title:string
>> > >rake db:migrate
>>
>> > now I visit /posts/new in my browser, use firebug to delete or change
>> > the authenticity token, and submit the form.
>>
>> > rails 2.3.11: all fine, new post saved
>> > rails 2.3.10: ActionController::InvalidAuthenticityToken
>>
>> > I checked ApplicationController to see if it still contained
>> > "protect_from_forgery", which is the case.
>> > I read the announcement for the csrf changes in 2.3.11 and they talk
>> > about overriding handle_unverified_request for special cases where
>> > there are other ways for authenticating a user. In this simple case I
>> > demonstrated though, there is no concept of a user or logging in (or a
>> > session), so the default action of resetting the session is not very
>> > useful.
>> > In my opinion, CSRF protection is about verifying a request. It
>> > doesn't have anything to do with users/sessions/authentication.
>> > By default, a faulty request (unprotected/wrong token) should not
>> > reach the normal controller action code at all, so the main action to
>> > take when a non-verified request comes in, is to have the
>> > before_filter chain halt. nothing more, nothing less.
>> > Extra stuff (like destroying a session) is up to the user (or nice to
>> > leave in as a default).
>> > So I think the behavior in 2.3.11 is just wrong, because in the
>> > example I gave, the forms just get submitted and stuff gets persisted
>> > to the database.
>> > It's not clear from the announcement at all that you should now make
>> > sure the filter chain halts, or that you must protect your actions by
>> > something that's stored in the session (because that's all that gets
>> > done when a faulty request hits).
>>
>> > Maybe I'm just doing something wrong here, please let me know.
>> > Mathijs
>>
>> --http://jonathanleighton.com/
>>
>> signature.asc
>> < 1KViewDownload
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Cheers
Koz
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