module ActionController::RequestForgeryProtection

Included modules:: AbstractController::Helpers, AbstractController::Callbacks

Controller actions are protected from Cross-Site Request Forgery (CSRF) attacks by including a token in the rendered html for your application. This token is stored as a random string in the session, to which an attacker does not have access. When a request reaches your application, Rails verifies the received token with the token in the session. Only HTML and JavaScript requests are checked, so this will not protect your XML API (presumably you'll have a different authentication scheme there anyway).

GET requests are not protected since they don't have side effects like writing to the database and don't leak sensitive information. JavaScript requests are an exception: a third-party site can use a <script> tag to reference a JavaScript URL on your site. When your JavaScript response loads on their site, it executes. With carefully crafted JavaScript on their end, sensitive data in your JavaScript response may be extracted. To prevent this, only XmlHttpRequest (known as XHR or Ajax) requests are allowed to make GET requests for JavaScript responses.

It's important to remember that XML or JSON requests are also affected and if you're building an API you'll need something like:

class ApplicationController < ActionController::Base
  protect_from_forgery
  skip_before_action :verify_authenticity_token, if: :json_request?

  protected

  def json_request?
    request.format.json?
  end
end

CSRF protection is turned on with the protect_from_forgery method, which checks the token and resets the session if it doesn't match what was expected. A call to this method is generated for new Rails applications by default.

The token parameter is named authenticity_token by default. The name and value of this token must be added to every layout that renders forms by including csrf_meta_tags in the html head.

Learn more about CSRF attacks and securing your application in the Ruby on Rails Security Guide.

Constants

CROSS_ORIGIN_JAVASCRIPT_WARNING

Protected Instance Methods

form_authenticity_param() Show source

The form's authenticity parameter. Override to provide your own.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 254
def form_authenticity_param
  params[request_forgery_protection_token]
end

form_authenticity_token() Show source

Sets the token value for the current session.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 249
def form_authenticity_token
  session[:_csrf_token] ||= SecureRandom.base64(32)
end

handle_unverified_request() Show source

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 201
def handle_unverified_request
  forgery_protection_strategy.new(self).handle_unverified_request
end

mark_for_same_origin_verification!() Show source

GET requests are checked for cross-origin JavaScript after rendering.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 222
def mark_for_same_origin_verification!
  @marked_for_same_origin_verification = request.get?
end

marked_for_same_origin_verification?() Show source

If the `verify_authenticity_token` before_action ran, verify that JavaScript responses are only served to same-origin GET requests.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 228
def marked_for_same_origin_verification?
  @marked_for_same_origin_verification ||= false
end

non_xhr_javascript_response?() Show source

Check for cross-origin JavaScript responses.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 233
def non_xhr_javascript_response?
  content_type =~ %r(\Atext/javascript) && !request.xhr?
end

protect_against_forgery?() Show source

Checks if the controller allows forgery protection.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 259
def protect_against_forgery?
  allow_forgery_protection
end

verified_request?() Show source

Returns true or false if a request is verified. Checks:

is it a GET or HEAD request? Gets should be safe and idempotent
Does the #form_authenticity_token match the given token value from the params?
Does the X-CSRF-Token header match the #form_authenticity_token

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 242
def verified_request?
  !protect_against_forgery? || request.get? || request.head? ||
    form_authenticity_token == params[request_forgery_protection_token] ||
    form_authenticity_token == request.headers['X-CSRF-Token']
end

verify_authenticity_token() Show source

The actual before_action that is used to verify the CSRF token. Don't override this directly. Provide your own forgery protection strategy instead. If you override, you'll disable same-origin `<script>` verification.

Lean on the protect_from_forgery declaration to mark which actions are due for same-origin request verification. If protect_from_forgery is enabled on an action, this before_action flags its after_action to verify that JavaScript responses are for XHR requests, ensuring they follow the browser's same-origin policy.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 192
def verify_authenticity_token
  mark_for_same_origin_verification!

  if !verified_request?
    logger.warn "Can't verify CSRF token authenticity" if logger
    handle_unverified_request
  end
end

verify_same_origin_request() Show source

If `verify_authenticity_token` was run (indicating that we have forgery protection enabled for this request) then also verify that we aren't serving an unauthorized cross-origin response.

# File actionpack/lib/action_controller/metal/request_forgery_protection.rb, line 214
def verify_same_origin_request
  if marked_for_same_origin_verification? && non_xhr_javascript_response?
    logger.warn CROSS_ORIGIN_JAVASCRIPT_WARNING if logger
    raise ActionController::InvalidCrossOriginRequest, CROSS_ORIGIN_JAVASCRIPT_WARNING
  end
end