module ActionController #:nodoc: class InvalidAuthenticityToken < ActionControllerError #:nodoc: end module RequestForgeryProtection def self.included(base) base.class_eval do class_inheritable_accessor :request_forgery_protection_options self.request_forgery_protection_options = {} helper_method :form_authenticity_token helper_method :protect_against_forgery? end base.extend(ClassMethods) end module ClassMethods # Protect a controller's actions from CSRF attacks by ensuring that all forms are coming from the current web application, not # a forged link from another site. This is done by embedding a token based on the session (which an attacker wouldn't know) in # all forms and Ajax requests generated by Rails and then verifying the authenticity of that token in the controller. Only # HTML/JavaScript requests are checked, so this will not protect your XML API (presumably you'll have a different authentication # scheme there anyway). Also, GET requests are not protected as these should be indempotent anyway. # # You turn this on with the #protect_from_forgery method, which will perform the check and raise # an ActionController::InvalidAuthenticityToken if the token doesn't match what was expected. And it will add # a _authenticity_token parameter to all forms that are automatically generated by Rails. You can customize the error message # given through public/422.html. # # Learn more about CSRF (Cross-Site Request Forgery) attacks: # # * http://isc.sans.org/diary.html?storyid=1750 # * http://en.wikipedia.org/wiki/Cross-site_request_forgery # # Keep in mind, this is NOT a silver-bullet, plug 'n' play, warm security blanket for your rails application. # There are a few guidelines you should follow: # # * Keep your GET requests safe and idempotent. More reading material: # * http://www.xml.com/pub/a/2002/04/24/deviant.html # * http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1 # * Make sure the session cookies that Rails creates are non-persistent. Check in Firefox and look for "Expires: at end of session" # # If you need to construct a request yourself, but still want to take advantage of forgery protection, you can grab the # authenticity_token using the form_authenticity_token helper method and make it part of the parameters yourself. # # Example: # # class FooController < ApplicationController # # uses the cookie session store (then you don't need a separate :secret) # protect_from_forgery :except => :index # # # uses one of the other session stores that uses a session_id value. # protect_from_forgery :secret => 'my-little-pony', :except => :index # # # you can disable csrf protection on controller-by-controller basis: # skip_before_filter :verify_authenticity_token # end # # If you are upgrading from Rails 1.x, disable forgery protection to # simplify your tests. Add this to config/environments/test.rb: # # # Disable request forgery protection in test environment # config.action_controller.allow_forgery_protection = false # # Valid Options: # # * :only/:except - passed to the before_filter call. Set which actions are verified. # * :secret - Custom salt used to generate the form_authenticity_token. # Leave this off if you are using the cookie session store. # * :digest - Message digest used for hashing. Defaults to 'SHA1' def protect_from_forgery(options = {}) self.request_forgery_protection_token ||= :authenticity_token before_filter :verify_authenticity_token, :only => options.delete(:only), :except => options.delete(:except) request_forgery_protection_options.update(options) end end protected # The actual before_filter that is used. Modify this to change how you handle unverified requests. def verify_authenticity_token verified_request? || raise(ActionController::InvalidAuthenticityToken) end # Returns true or false if a request is verified. Checks: # # * is the format restricted? By default, only HTML and AJAX requests are checked. # * is it a GET request? Gets should be safe and idempotent # * Does the form_authenticity_token match the given _token value from the params? def verified_request? !protect_against_forgery? || request.method == :get || !verifiable_request_format? || form_authenticity_token == params[request_forgery_protection_token] end def verifiable_request_format? request.format.html? || request.format.js? end # Sets the token value for the current session. Pass a :secret option in #protect_from_forgery to add a custom salt to the hash. def form_authenticity_token @form_authenticity_token ||= if request_forgery_protection_options[:secret] authenticity_token_from_session_id elsif session.respond_to?(:dbman) && session.dbman.respond_to?(:generate_digest) authenticity_token_from_cookie_session elsif session.nil? raise InvalidAuthenticityToken, "Request Forgery Protection requires a valid session. Use #allow_forgery_protection to disable it, or use a valid session." else raise InvalidAuthenticityToken, "No :secret given to the #protect_from_forgery call. Set that or use a session store capable of generating its own keys (Cookie Session Store)." end end # Generates a unique digest using the session_id and the CSRF secret. def authenticity_token_from_session_id key = if request_forgery_protection_options[:secret].respond_to?(:call) request_forgery_protection_options[:secret].call(@session) else request_forgery_protection_options[:secret] end digest = request_forgery_protection_options[:digest] ||= 'SHA1' OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new(digest), key.to_s, session.session_id.to_s) end # No secret was given, so assume this is a cookie session store. def authenticity_token_from_cookie_session session[:csrf_id] ||= CGI::Session.generate_unique_id session.dbman.generate_digest(session[:csrf_id]) end def protect_against_forgery? allow_forgery_protection && request_forgery_protection_token end end end