5 files changed, 21 insertions, 8 deletions
diff --git a/actioncable/CHANGELOG.md b/actioncable/CHANGELOG.md
index 137c88d91b..d70d32ce07 100644
--- a/actioncable/CHANGELOG.md
+++ b/actioncable/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Permit same-origin connections by default.
+
+    New option `config.action_cable.allow_same_origin_as_host = false`
+    to disable.
+
+    *Dávid Halász*, *Matthew Draper*
+
 *   Prevent race where the client could receive and act upon a
     subscription confirmation before the channel's `subscribed` method
     completed.
diff --git a/actioncable/README.md b/actioncable/README.md
index 30b86edd2e..8ad9aeb1f1 100644
--- a/actioncable/README.md
+++ b/actioncable/README.md
@@ -326,7 +326,10 @@ Rails.application.paths.add "config/cable", with: "somewhere/else/cable.yml"
 
 ### Allowed Request Origins
 
-Action Cable will only accept requests from specified origins, which are passed to the server config as an array. The origins can be instances of strings or regular expressions, against which a check for match will be performed.
+Action Cable will only accept requests from specific origins.
+
+By default, only an origin matching the cable server itself will be permitted.
+Additional origins can be specified using strings or regular expressions, provided in an array.
 
 ```ruby
 Rails.application.config.action_cable.allowed_request_origins = ['http://rubyonrails.com', /http:\/\/ruby.*/]
@@ -334,15 +337,17 @@ Rails.application.config.action_cable.allowed_request_origins = ['http://rubyonr
 
 When running in the development environment, this defaults to "http://localhost:3000".
 
-To disable and allow requests from any origin:
+To disable protection and allow requests from any origin:
 
 ```ruby
 Rails.application.config.action_cable.disable_request_forgery_protection = true
 ```
 
-It is also possible to allow origins that are starting with the actual HTTP HOST header:
+To disable automatic access for same-origin requests, and strictly allow
+only the configured origins:
+
 ```ruby
-Rails.application.config.action_cable.allow_same_origin_as_host = true
+Rails.application.config.action_cable.allow_same_origin_as_host = false
 ```
 
 ### Consumer Configuration
diff --git a/actioncable/lib/action_cable/connection/base.rb b/actioncable/lib/action_cable/connection/base.rb
index 2596635701..dfee123ea2 100644
--- a/actioncable/lib/action_cable/connection/base.rb
+++ b/actioncable/lib/action_cable/connection/base.rb
@@ -196,9 +196,9 @@ module ActionCable
           return true if server.config.disable_request_forgery_protection
 
           proto = Rack::Request.new(env).ssl? ? "https" : "http"
-          if Array(server.config.allowed_request_origins).any? { |allowed_origin|  allowed_origin === env["HTTP_ORIGIN"] }
+          if server.config.allow_same_origin_as_host && env["HTTP_ORIGIN"] == "#{proto}://#{env['HTTP_HOST']}"
             true
-          elsif server.config.allow_same_origin_as_host && env["HTTP_ORIGIN"] == "#{proto}://#{env['HTTP_HOST']}"
+          elsif Array(server.config.allowed_request_origins).any? { |allowed_origin|  allowed_origin === env["HTTP_ORIGIN"] }
             true
           else
             logger.error("Request origin not allowed: #{env['HTTP_ORIGIN']}")
diff --git a/actioncable/lib/action_cable/server/configuration.rb b/actioncable/lib/action_cable/server/configuration.rb
index aa8d10b3d4..17e0dee064 100644
--- a/actioncable/lib/action_cable/server/configuration.rb
+++ b/actioncable/lib/action_cable/server/configuration.rb
@@ -15,7 +15,7 @@ module ActionCable
         @worker_pool_size = 4
 
         @disable_request_forgery_protection = false
-        @allow_same_origin_as_host = false
+        @allow_same_origin_as_host = true
       end
 
       # Returns constant of subscription adapter specified in config/cable.yml.
diff --git a/actioncable/test/connection/cross_site_forgery_test.rb b/actioncable/test/connection/cross_site_forgery_test.rb
index 6cabff5440..37bedfd734 100644
--- a/actioncable/test/connection/cross_site_forgery_test.rb
+++ b/actioncable/test/connection/cross_site_forgery_test.rb
@@ -13,12 +13,13 @@ class ActionCable::Connection::CrossSiteForgeryTest < ActionCable::TestCase
   setup do
     @server = TestServer.new
     @server.config.allowed_request_origins = %w( http://rubyonrails.com )
+    @server.config.allow_same_origin_as_host = false
   end
 
   teardown do
     @server.config.disable_request_forgery_protection = false
     @server.config.allowed_request_origins = []
-    @server.config.allow_same_origin_as_host = false
+    @server.config.allow_same_origin_as_host = true
   end
 
   test "disable forgery protection" do