vendor/rails/actionpack/lib/action_controller/request_forgery_protection.rb

   1 module ActionController #:nodoc:
   2   class InvalidAuthenticityToken < ActionControllerError #:nodoc:
   3   end
   4
   5   module RequestForgeryProtection
   6     def self.included(base)
   7       base.class_eval do
   8         helper_method :form_authenticity_token
   9         helper_method :protect_against_forgery?
  10       end
  11       base.extend(ClassMethods)
  12     end
  13
  14     # Protecting controller actions from CSRF attacks by ensuring that all forms are coming from the current web application, not a
  15     # forged link from another site, is done by embedding a token based on a random string stored in the session (which an attacker wouldn't know) in all
  16     # forms and Ajax requests generated by Rails and then verifying the authenticity of that token in the controller.  Only
  17     # HTML/JavaScript requests are checked, so this will not protect your XML API (presumably you'll have a different authentication
  18     # scheme there anyway).  Also, GET requests are not protected as these should be idempotent anyway.
  19     #
  20     # This is turned on with the <tt>protect_from_forgery</tt> method, which will check the token and raise an
  21     # ActionController::InvalidAuthenticityToken if it doesn't match what was expected. You can customize the error message in
  22     # production by editing public/422.html.  A call to this method in ApplicationController is generated by default in post-Rails 2.0
  23     # applications.
  24     #
  25     # The token parameter is named <tt>authenticity_token</tt> by default. If you are generating an HTML form manually (without the
  26     # use of Rails' <tt>form_for</tt>, <tt>form_tag</tt> or other helpers), you have to include a hidden field named like that and
  27     # set its value to what is returned by <tt>form_authenticity_token</tt>. Same applies to manually constructed Ajax requests. To
  28     # make the token available through a global variable to scripts on a certain page, you could add something like this to a view:
  29     #
  30     #   <%= javascript_tag "window._token = '#{form_authenticity_token}'" %>
  31     #
  32     # Request forgery protection is disabled by default in test environment.  If you are upgrading from Rails 1.x, add this to
  33     # config/environments/test.rb:
  34     #
  35     #   # Disable request forgery protection in test environment
  36     #   config.action_controller.allow_forgery_protection = false
  37     #
  38     # == Learn more about CSRF (Cross-Site Request Forgery) attacks
  39     #
  40     # Here are some resources:
  41     # * http://isc.sans.org/diary.html?storyid=1750
  42     # * http://en.wikipedia.org/wiki/Cross-site_request_forgery
  43     #
  44     # Keep in mind, this is NOT a silver-bullet, plug 'n' play, warm security blanket for your rails application.
  45     # There are a few guidelines you should follow:
  46     #
  47     # * Keep your GET requests safe and idempotent.  More reading material:
  48     #   * http://www.xml.com/pub/a/2002/04/24/deviant.html
  49     #   * http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
  50     # * Make sure the session cookies that Rails creates are non-persistent.  Check in Firefox and look for "Expires: at end of session"
  51     #
  52     module ClassMethods
  53       # Turn on request forgery protection. Bear in mind that only non-GET, HTML/JavaScript requests are checked.
  54       #
  55       # Example:
  56       #
  57       #   class FooController < ApplicationController
  58       #     protect_from_forgery :except => :index
  59       #
  60       #     # you can disable csrf protection on controller-by-controller basis:
  61       #     skip_before_filter :verify_authenticity_token
  62       #   end
  63       #
  64       # Valid Options:
  65       #
  66       # * <tt>:only/:except</tt> - Passed to the <tt>before_filter</tt> call.  Set which actions are verified.
  67       def protect_from_forgery(options = {})
  68         self.request_forgery_protection_token ||= :authenticity_token
  69         before_filter :verify_authenticity_token, :only => options.delete(:only), :except => options.delete(:except)
  70         if options[:secret] || options[:digest]
  71           ActiveSupport::Deprecation.warn("protect_from_forgery only takes :only and :except options now. :digest and :secret have no effect", caller)
  72         end
  73       end
  74     end
  75
  76     protected
  77       # The actual before_filter that is used.  Modify this to change how you handle unverified requests.
  78       def verify_authenticity_token
  79         verified_request? || raise(ActionController::InvalidAuthenticityToken)
  80       end
  81
  82       # Returns true or false if a request is verified.  Checks:
  83       #
  84       # * is the format restricted?  By default, only HTML and AJAX requests are checked.
  85       # * is it a GET request?  Gets should be safe and idempotent
  86       # * Does the form_authenticity_token match the given token value from the params?
  87       def verified_request?
  88         !protect_against_forgery?     ||
  89           request.method == :get      ||
  90           !verifiable_request_format? ||
  91           form_authenticity_token == params[request_forgery_protection_token]
  92       end
  93
  94       def verifiable_request_format?
  95         !request.content_type.nil? && request.content_type.verify_request?
  96       end
  97
  98       # Sets the token value for the current session.  Pass a <tt>:secret</tt> option
  99       # in +protect_from_forgery+ to add a custom salt to the hash.
 100       def form_authenticity_token
 101         session[:_csrf_token] ||= ActiveSupport::SecureRandom.base64(32)
 102       end
 103
 104       def protect_against_forgery?
 105         allow_forgery_protection && request_forgery_protection_token
 106       end
 107   end
 108 end