[jsr-314-open-mirror] [jsr-314-open] [Spec-869-Specify CSRF Solution] PROPOSAL(s)

Fri Oct 22 16:32:55 EDT 2010

Hi guys,

so my two cents on this issue, which were written on the train today,
and do not reflect that latest discussion:

@session token: can this be a unique token per request? I also don't
see the need for an extra-token, it might be enough to keep this in
the view-state key which is sent to the client. However, if we change
the derivation of the view-key, we should additionally provide an API
to access this.

With this, we could implement a basic server-side double-submit
tracking and back-button handling which is much better than we have
right now. It would actually be quite easy to do so: we could have a
phase-listener registered which knows about the list of processed
request tokens, and will identify which request is coming in relative
to this list. This of course will only work if the browser is not
allowed to cache the pages, but that would almost never make sense in
JSF anyways. All we would than need is a faces-artifact (name
HistoryHandler?) which gets notified if this was a refresh, a
back-button or a forward which was executed, also with the number of
relative steps in between the current page and the corresponding
back-button or forward. The application could then decide what to do
with this information (we could possibly provide a default
implementation). I believe this is one functionality which we should
have had since day one, and as it is so easy to implement with this
added request token, I think we should go for it. I would be willing
to sponsor whatever is necessary to get this in.

I agree with other commenters that the CSRF protection really makes
only sense per view - or actually, and this is hopefully a right
assumption, per what the view does. The idea is: if the view is
idempotent in the sense that it doesn't create any permanent changes
to the app-data (whatever that is), then it is not necessary to check
for the CSRF token - the CSRF attack will never get through to
anything useful then. So I would envision a configuration per view (in
the view metadata?) which would allow to mark the view as idempotent,
and hence exclude it from the CSRF checking. Does this make sense to
you guys?

best regards,

Martin

On 10/22/10, Blake Sullivan <blake.sullivan at oracle.com> wrote:
>   On 10/22/10 11:10 AM, Roger Kitain wrote:
>>  Hey Blake -
>>
>> Thanks for responses..
>>
>> On 10/22/10 12:51 PM, Blake Sullivan wrote:
>>>  Roger,
>>>
>>> Di you answer Alexander's question regarding whether this feature is
>>> even necessary?  In the current releases, with no explicit CSRF
>>> defenses, we have attacks against:
>>> 1) GET attack
>>> 2) POST attack against a page with token state saving
>>> 3) POST attack against a page with client state saving
>> Yes.  By number 2 - I presume you are talking about server side state
>> saving.
>>>
>>> 1) For GET attacks, it appears that we are saying that we aren't
>>> going to defend against these anyway for this release.
>> Yes. It's a bit trickier as we may need to do this on a page by page
>> basis.
> I think that it is trickier than that--you need to worry about things
> like your parameter leaking out through the referer header.  At this
> point, I don't see how you would get the spec work done in time.  Plus,
> a well written web application won't have side-effects on the GET
> anyway.  The CSRF attacker can GET all day and not change the
> application state.
>>>
>>> 2) For POST attacks against a page with token state saving.  As long
>>> as the view state token is cryptographically strong, the attacker
>>> can't guess the token anyway.  At that point, it comes down to what
>>> the behavior is for a request that has an invalid token--we can
>>> either return an error page or we can treat the request as a GET.  If
>>> we treat the request as a GET, we are in 1
>> For server side state saving by default, the view state is not as strong.
>>   So we were looking at
>> this CSRF "extra token" approach as facilitating the view state for
>> CSRF solution.  However, there are ways to make the server side view
>> state stronger - in which case there may not
>> be a need for an extra token to augment the view state.  For now it
>> may be as simple as a clarification
>> (recommendation) in the spec about the server side view state being
>> cryptographically strong - I'd have
>> to check the spec to see what is there.
> Yep.  Make it cryptographically strong, as it is in Trinidad and you are
> done with the server-side storage POST except for figuring out what to
> do if the token isn't valid.  I see no need to add yet another token
> when the existing one will do.
>>>
>>> 3) For POST attacks against a page with client state saving, as long
>>> as attackers can't forge the client state, they can't do anything.
>>> Since, they can't, we're safe here as well.
>> Yes, client side view state is cryptographically strong.
> Yep
>>>
>>> Therefore, it isn't clear what the feature is buying us.  If there is
>>> no clear need for the feature, it should not be added to the
>>> specification.
>> If we are deferring GET CSRF handling, and possibly adding a spec
>> clarification for server side view state, then I agree.
> Cool
>
> -- Blake Sullivan
>
>>>
>>> -- Blake Sullivan
>>>
>>>
>>> On 9/21/10 10:15 AM, Roger Kitain wrote:
>>>>
>>>> There are two proposals for enhancing CSRF attacks in JSF.  We need
>>>> to pick one.
>>>>
>>>> Proposal 1: Form Action URL Approach (Approach provided by Kito Mann)
>>>>
>>>> This approach does the following:      - Token is generated on the
>>>> server consisting (minimally) of a randomly generated "secret key
>>>>      (stored in session).
>>>>    - ViewHandler.getActionURL method must include the token parameter
>>>>      named "javax.faces.Token", and whose value is the token value.
>>>>    - At render time this token will be included in Form's action URL
>>>> - and it will be
>>>>      posted back to the server.
>>>>    - Restore View Phase processing compares the incoming token
>>>> request parameter value
>>>>      with the token value generated from the secret key in the session.
>>>>
>>>> Spec Document Modifications:
>>>>
>>>> Section 7.5.1:
>>>>
>>>> getActionURL:
>>>>
>>>> "The URL must contain the parameter constant defined by
>>>> ResponseStateManager.VIEW_TOKEN_PARAM
>>>> The value of this parameter must be a cryptographically produced
>>>> value minimally consisting
>>>> of a "secret key". The "secret key" is a random generated value that
>>>> was stored in the session
>>>> (preferably around session creation time).  Implementations may also
>>>> choose to combine other
>>>> values with the secret key to produce a more complex token."
>>>>
>>>> Section 2.2.1
>>>>
>>>>  "Verify the "javax.faces.Token" request parameter value is the same
>>>> as the token value generated
>>>>    from the "secret key" stored in the session.  If the values do
>>>> not match, throw a meaningful
>>>>    exception."
>>>>
>>>>
>>>> Proposal 2: Form Hidden Field Approach
>>>>
>>>> This approach is similar to Approach 1, except a Form hidden field
>>>> "javax.faces.Token"
>>>> is used instead of appending to the Form's Action URL.
>>>>
>>>> Spec Document Modifications:
>>>>
>>>> Standard RenderKit Docs
>>>>
>>>> - Form Rendering
>>>>
>>>> "Render a hidden field named "javax.faces.Token" using the
>>>> ResponseStateManager.VIEW_TOKEN_PARAM
>>>>  constant.  The value of this hidden field is a cryptographically
>>>> produced value that must at least
>>>>  consist of a "secret key".  The "secret key" is a random generated
>>>> value that was stored in the
>>>>  session (preferably around session creation time).  Implementations
>>>> may also choose to combine
>>>>  other values with the secret key to produce a more complex token."
>>>>
>>>> Specification Document
>>>>
>>>> Section 2.2.1
>>>>   "Verify the "javax.faces.Token" request parameter value is the
>>>> same as the token value generated
>>>>    from the "secret key" stored in the session.  If the values do
>>>> not match, throw a FacesException.
>>>>
>>>>
>>>> For both approaches see:
>>>>
>>>>
>>>> [1]
>>>> https://javaserverfaces-spec-public.dev.java.net/issues/show_bug.cgi?id=869
>>>>
>>>> Look at the two latest change bundles attached to the issue.
>>>>
>>>> Please review by COB Friday as we have no time left for 2.1.
>>>>
>>>> Kudos to Kito Mann for helping out with the implementation.
>>>>
>>>> -roger
>>>
>>
>>
>
>

-- 

http://www.irian.at

Your JSF powerhouse -
JSF Consulting, Development and
Courses in English and German

Professional Support for Apache MyFaces