ruby on rails - ActionController::InvalidAuthenticityToken

Question

Below is an error, caused by a form in my Rails application:

Processing UsersController#update (for **ip** at 2010-07-29 10:52:27) [PUT]
  Parameters: {"commit"=>"Update", "action"=>"update", "_method"=>"put", "authenticity_token"=>"ysiDvO5s7qhJQrnlSR2+f8jF1gxdB7T9I2ydxpRlSSk=", **more parameters**}

ActionController::InvalidAuthenticityToken (ActionController::InvalidAuthenticityToken):

This happens for every non-get request and, as you see, authenticity_token is there.

Answer 1

I had the same issue but with pages which were page cached. Pages got buffered with a stale authenticity token and all actions using the methods post/put/delete where recognized as forgery attempts. Error (422 Unprocessable Entity) was returned to the user.

The solution for Rails 3:
Add:

 skip_before_filter :verify_authenticity_token  

or as "sagivo" pointed out in Rails 4 add:

 skip_before_action :verify_authenticity_token

On pages which do caching.

As @toobulkeh commented this is not a vulnerability on :index, :show actions, but beware using this on :put, :post actions.

For example:

 caches_page :index, :show  
 skip_before_filter :verify_authenticity_token, :only => [:index, :show]

Reference: http://api.rubyonrails.org/classes/ActionController/RequestForgeryProtection/ClassMethods.html

Note added by barlop- Rails 4.2 deprecated skip_before_filter in favour of skip_before_action https://guides.rubyonrails.org/4_2_release_notes.html "The *_filter family of methods have been removed from the documentation. Their usage is discouraged in favor of the *_action family of methods"

For Rails 6 (as "collimarco" pointed out) you can use skip_forgery_protection and that it is safe to use it for a REST API that doesn't use session data.