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Don't check authenticity tokens for any AJAX requests

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commit 256b0ee8e3c1610967dfc89f864e24b98ed3c236 1 parent 3c11876
authored March 04, 2009 wycats committed April 15, 2009
2  actionpack/CHANGELOG
@@ -7,6 +7,8 @@
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 * Fixed that redirection would just log the options, not the final url (which lead to "Redirected to #<Post:0x23150b8>") [DHH]
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+* Don't check authenticity tokens for any AJAX requests [Ross Kaffenberger/Bryan Helmkamp]
  11
+
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 * Added ability to pass in :public => true to fresh_when, stale?, and expires_in to make the request proxy cachable #2095 [Gregg Pollack]
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 * Fixed that passing a custom form builder would be forwarded to nested fields_for calls #2023 [Eloy Duran/Nate Wiger]
3  actionpack/lib/action_controller/base/request_forgery_protection.rb
@@ -81,12 +81,13 @@ def verify_authenticity_token
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       # Returns true or false if a request is verified.  Checks:
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       #
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-      # * is the format restricted?  By default, only HTML and AJAX requests are checked.
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+      # * is the format restricted?  By default, only HTML requests are checked.
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       # * is it a GET request?  Gets should be safe and idempotent
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       # * Does the form_authenticity_token match the given token value from the params?
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       def verified_request?
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         !protect_against_forgery?     ||
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           request.method == :get      ||
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+          request.xhr?                ||
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           !verifiable_request_format? ||
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           form_authenticity_token == params[request_forgery_protection_token]
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       end
11  actionpack/test/controller/request_forgery_protection_test.rb
@@ -151,14 +151,10 @@ def test_should_not_allow_api_formatted_delete_sent_as_multipart_form_without_to
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       delete :index, :format => 'xml'
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     end
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   end
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-
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+  
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   def test_should_allow_xhr_post_without_token
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     assert_nothing_raised { xhr :post, :index }
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   end
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-  def test_should_not_allow_xhr_post_with_html_without_token
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-    @request.env['CONTENT_TYPE'] = Mime::URL_ENCODED_FORM.to_s
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-    assert_raise(ActionController::InvalidAuthenticityToken) { xhr :post, :index }
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-  end
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   def test_should_allow_xhr_put_without_token
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     assert_nothing_raised { xhr :put, :index }
@@ -168,6 +164,11 @@ def test_should_allow_xhr_delete_without_token
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     assert_nothing_raised { xhr :delete, :index }
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   end
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+  def test_should_allow_xhr_post_with_encoded_form_content_type_without_token
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+    @request.env['CONTENT_TYPE'] = Mime::URL_ENCODED_FORM.to_s
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+    assert_nothing_raised { xhr :post, :index }
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+  end
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+  
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   def test_should_allow_post_with_token
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     post :index, :authenticity_token => @token
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     assert_response :success

36 notes on commit 256b0ee

Manfred Stienstra

Yehuda, can you explain this commit? Is this associated with a Lighthouse ticket somehow?

Nathan Sutton
nate commented on 256b0ee April 16, 2009

Why was this removed?

Jason Roelofs

Um, wasn’t half the point of Auth Tokens security against rogue AJAX requests? What is the point of this commit?

Norbert Crombach

Yeah, this seems odd.

Yehuda Katz
Owner

@jameskilton rogue Ajax requests cannot produce CSRF attacks, so this was just an annoyance to people hand-writing JS.

Carl Lerche
Collaborator

jameskilton: If you can make a rogue AJAX request, you have bigger problems than CSRF attacks ;)

Dimitri Krassovski

At last, no dumb tokens to generate by hand =)

Yehuda Katz
Owner

@labria at last… a positive comment on this change! W00H00!

Lucas Húngaro

Very nice indeed. :)

Michael Koziarski
Owner

The same original policy protects ajax requests. you can’t make browsers submit forms or make requests with custom headers.

This should be safe until browsers drop the same origin policy, which is (one hopes) forever.

Adrian Pacała

Why thank you kind sir. No more ugly inline JS only for that one pesky line of auth token.

Geoff Buesing
Collaborator

This is also a big win for cacheability, because we can remove user-specific authenticity tokens from ajaxified links and forms that don’t need to support a non-ajax fallthrough.

Very nice!

Matt White

Excellent! This was a pain when implementing unobtrusive JS…

Joost Baaij

I don’t understand this commit. What’s stopping an attacker who is compiling a browser herself and making different-origin a reality? Now the security of Rails apps is tied to ‘hopes’ of third parties doing the right thing?

Samuel Lebeau

@tilsammans: I believe CSRF protection is only useful to prevent users from doing cross-site requests without knowing it (i.e. submitting a form whose

action
is on another site where he’s authenticated). If one compiles its own browser making different-origin a reality as you suggested, he will be the only one in danger. Am I missing something here ?
Samuel Lebeau

Sorry about the preformatted tag above… having previews or comment edition would be such a nice feature ;)

Radoslav Stankov

Really great addition, will save me a lot unnecessary hacking :)

@tilsammans As far as I know protected_from_forgery, is for securing the frontend users, from other users/sites/scripts, who tried to pretend to be the frontend user. I mean that a person who is compiling a browser himself, for example, could only take his session data, witch is his. This is the same as that I could change the html with FireBug and fire some forms, run ajax queries, and other things from every site.

milodurden

So what happens when someone posts a CSRF request with the header ‘X-Requested-With’ set to ‘XMLHttpRequest’ ?

Michael Koziarski
Owner

@mildodurden: You can’t do that with browsers as they exist currently. If you can prove otherwise, please let us know and we can revert this.

Michael Koziarski
Owner

@tilsammans: If the attacker is executing custom browsers on the user’s computer, there’s nothing we can do about it. They could also be running keyloggers, screenshotters, botnets etc.

This is for protecting against CSRF attacks, not a silver bullet for all possible attacks ever inventable.

Yehuda Katz
Owner

For further details on CSRF, check out this great Stanford paper:

XMLHttpRequest’s popularity has increased recently with more sites implementing AJAX interfaces. Sites can defend against CSRF by setting a custom header via XMLHttpRequest and validating that the header is present before processing state-modifying requests. Although effective, this defense requires sites to make all state-modifying requests via XMLHttpRequest, a requirement that prevents many natural site designs.
Arthur Zapparoli

Any chance to see this change on 2.3 branch? :)

Arthur Schreiber

+1 for a backport! :)

José Valim
Owner

+1 for a backport!

Sam Granieri

+1 for a backport

Nathan Sutton
nate commented on 256b0ee April 19, 2009

You could backport it in a backwards compatible way. Check it if it’s included, otherwise ignore it.

Sarah Allen

+1 for for 2.3

Sarah Allen

Just saw binary42’s response. There reason to backport it, is that new code is still being written for Rails and this is a stumbling block when you want to make requests from Ajax, desktop client, or Flash. I don’t see this as a policy change, so much as a bug fix. (But I’m new to Rails, maybe I’m missing something)

Paul Rosania

What about local XSS attacks? With unescaped output, something akin to the MySpace worm is enabled by this change.

Granted, Rails coders always remember to escape output! :) But was the intent to remove a layer of defensive programming?

Sarah Allen

-1 for 2.3 (revised vote)

@binary42 after thinking about this more this morning, I realized that changing the behavior in a dot release is probably unwise. If there is an existing app depending on this behavior with an open cross-domain.xml and using cookie-based authentication, then a malicious flash app hosted on another site could make requests on behalf of a user without them being aware of it.

In terms of the “5 minute” fix… I’m still struggling to find the right few lines of code to write. I thought it work would to add the following to my controller:

 
def verify_authenticity_token 
  request.xhr?      || 
  verified_request? ||  
  raise(ActionController::InvalidAuthenticityToken) 
end 

but I still get the exception. I’m sure I’m missing something basic. Is the code change I need to make documented somewhere?

Thanks!

Geoff Buesing
Collaborator

@ultrasaurus for a quick 2.3 patch, check out this gist: http://gist.github.com/98660 . You can put this an initializer and it should work

Arthur Schreiber

@paulrosania: If your users are able to execute JavaScript through a XSS, this authenticity token won't be able to prevent CSRFs at all. It would be a snap to fetch the authenticity token from a page which has a form on it...

@everyone else who wants to see this in 2.3: http://gist.github.com/99635 <- a simple initializer like the one of gbuesing, but not using class eval.

Michael Koziarski
Owner

@paulrosania: In fact the twitter worm did exactly what NoKarma is describing. XSS is the stack-smashing of web attacks, if you're attacked you're done. Nothing can save you

Vladimir Rybas
vrybas commented on 256b0ee May 04, 2009

@ultrasaurus:
skip_before_filter :verify_authenticity_token, :only => [:aircrafts_by_manufacturer]
?

Michael Koziarski
Owner
NZKoz commented on 256b0ee May 04, 2009

@vrybas: instead of explicitly skipping the filter you should do:

protect_from_forgery :except=>[:aircrafts_by_manufacturer]

I'm also reasonably sure that you could do something along the lines of

protect_from_forgery :if=>:some_method_which_returns_true_when_ajax_or_whatever

Jeff Dwyer

Isn't it pretty easy to add authenticity_tokens to all ajax requests? ie these 7 lines of code? http://gist.github.com/149110

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