Protect against CSRF token fixation attacks

Author: José Valim

lib/devise.rb

@@ -223,6 +223,10 @@ module Strategies
   mattr_accessor :omniauth_path_prefix
   @@omniauth_path_prefix = nil
 
+  # Set if we should clean up the CSRF Token on authentication
+  mattr_accessor :clean_up_csrf_token_on_authentication
+  @@clean_up_csrf_token_on_authentication = true
+
   def self.encryptor=(value)
     warn "\n[DEVISE] To select a encryption which isn't bcrypt, you should use devise-encryptable gem.\n"
   end

lib/devise/hooks/csrf_cleaner.rb

@@ -0,0 +1,5 @@
+Warden::Manager.after_authentication do |record, warden, options|
+  if Devise.clean_up_csrf_token_on_authentication
+    warden.request.session.try(:delete, :_csrf_token)
+  end
+end

lib/devise/models/authenticatable.rb

@@ -1,4 +1,5 @@
 require 'devise/hooks/activatable'
+require 'devise/hooks/csrf_cleaner'
 
 module Devise
   module Models

lib/generators/templates/devise.rb

@@ -76,6 +76,12 @@
   # passing :skip => :sessions to `devise_for` in your config/routes.rb
   config.skip_session_storage = [:http_auth]
 
+  # By default, Devise cleans up the CSRF token on authentication to
+  # avoid CSRF token fixation attacks. This means that, when using AJAX
+  # requests for sign in and sign up, you need to get a new CSRF token
+  # from the server. You can disable this option at your own risk.
+  # config.clean_up_csrf_token_on_authentication = true
+
   # ==> Configuration for :database_authenticatable
   # For bcrypt, this is the cost for hashing the password and defaults to 10. If
   # using other encryptors, it sets how many times you want the password re-encrypted.

test/integration/authenticatable_test.rb

@@ -327,6 +327,20 @@ class AuthenticationSessionTest < ActionDispatch::IntegrationTest
     assert_redirected_to new_user_session_path
   end
 
+  test 'refreshes _csrf_token' do
+    ApplicationController.allow_forgery_protection = true
+
+    begin
+      get new_user_session_path
+      token = request.session[:_csrf_token]
+
+      sign_in_as_user
+      assert_not_equal request.session[:_csrf_token], token
+    ensure
+      ApplicationController.allow_forgery_protection = false
+    end
+  end
+
   test 'allows session to be set for a given scope' do
     sign_in_as_user
     get '/users'