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

Kito Mann kito.mann at virtua.com
Tue Oct 26 14:01:18 EDT 2010 

On Mon, Oct 25, 2010 at 8:14 PM, Blake Sullivan
<blake.sullivan at oracle.com> wrote:
>
> This leaves the ever popular GETs.  I'm probably being lazy, but at this
> point I'm willing to punt on GETs because of potential problems with:
>
> 1) Worries about referer leakage if the secret is encoded in the URL
> 2) How to deal with bookmarking
> 3) General dislike for ugly URLs
>
> Admittedly, I think that 2) is the only one that really requires more
> thought, since I think that the solution to 1) is to a) Only worry about
> CSRF for pages served through a secure channel b) Require that pages served
> to authenticated users be served through a secure channel.  For 3), I think
> it's gross but, that's just me :)

I think leaving out support for GETs is a bad idea. The OWSAP site
states it quite well:

The ideal solution is to only include the CSRF token in POST requests
and modify server-side actions that have state changing affect to only
respond to POST requests. If sensitive server-side actions are
guaranteed to only ever respond to POST requests, then there is no
need to include the token in GET requests. In most JavaEE web
applications, however, HTTP method scoping is rarely ever utilized
when retrieving HTTP parameters from a request. Calls to
"HttpServletRequest.getParameter" will return a parameter value
regardless if it was a GET or POST.

See http://www.owasp.org/index.php/Cross-Site_Request_Forgery_%28CSRF%29_Prevention_Cheat_Sheet
for the entire page. Their sample filter handles GET requests.

We can all talk about how updates should only occur during a POST, but
that doesn't reflect reality -- there's nothing in JSF that enforces
this. Also, with JSF 2's support for view parameters, it's even easier
for developers to do unexpected things in GET requests.

I don't see how this solution is any weaker than the algorithm
proposed by OWSAP. Also, HDIV (http://www.hdiv.org/index.htm) which is
used to secure different types of Java web apps, supports GET
requests.

>
>
>
> -- Blake Sullivan
>
>
>
>
>> 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
>>>>
>>>
>>
>
>

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