Purpose Metadata For Signed And Encrypted Cookies

Purpose metadata prevents cookie values from being
copy-pasted and ensures that the cookie is used only
for its originally intended purpose.

The Purpose and Expiry metadata are embedded inside signed/encrypted
cookies and will not be readable on previous versions of Rails.

We can switch off purpose and expiry metadata embedded in
signed and encrypted cookies using

	config.action_dispatch.use_cookies_with_metadata = false

if you want your cookies to be readable on older versions of Rails.

5 files changed, 22 insertions, 10 deletions

diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index 31d0d65a30..99e42ebefb 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -267,6 +267,7 @@ module Rails
           "action_dispatch.cookies_serializer" => config.action_dispatch.cookies_serializer,
           "action_dispatch.cookies_digest" => config.action_dispatch.cookies_digest,
           "action_dispatch.cookies_rotations" => config.action_dispatch.cookies_rotations,
+          "action_dispatch.use_cookies_with_metadata" => config.action_dispatch.use_cookies_with_metadata,
           "action_dispatch.content_security_policy" => config.content_security_policy,
           "action_dispatch.content_security_policy_report_only" => config.content_security_policy_report_only,
           "action_dispatch.content_security_policy_nonce_generator" => config.content_security_policy_nonce_generator
diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index 9c54cc1f37..9eb07219e0 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -120,6 +120,10 @@ module Rails
           if respond_to?(:action_view)
             action_view.default_enforce_utf8 = false
           end
+
+          if respond_to?(:action_dispatch)
+            action_dispatch.use_cookies_with_metadata = true
+          end
         else
           raise "Unknown version #{target_version.to_s.inspect}"
         end
diff --git a/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_0.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_0.rb.tt
index 179b97de4a..54eb0cb1d2 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_0.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_0.rb.tt
@@ -8,3 +8,10 @@
 
 # Don't force requests from old versions of IE to be UTF-8 encoded
 # Rails.application.config.action_view.default_enforce_utf8 = false
+
+# Embed purpose and expiry metadata inside signed and encrypted
+# cookies for increased security.
+#
+# This option is not backwards compatible with earlier Rails versions.
+# It's best enabled when your entire app is migrated and stable on 6.0.
+# Rails.application.config.action_dispatch.use_cookies_with_metadata = true
diff --git a/railties/test/application/middleware/cookies_test.rb b/railties/test/application/middleware/cookies_test.rb
index ecb4ee3446..fe48ef3f03 100644
--- a/railties/test/application/middleware/cookies_test.rb
+++ b/railties/test/application/middleware/cookies_test.rb
@@ -110,14 +110,14 @@ module ApplicationTests
       assert_equal "signed cookie".inspect, last_response.body
 
       get "/foo/read_raw_cookie"
-      assert_equal "signed cookie", verifier_sha512.verify(last_response.body)
+      assert_equal "signed cookie", verifier_sha512.verify(last_response.body, purpose: "cookie.signed_cookie")
 
       get "/foo/write_raw_cookie_sha256"
       get "/foo/read_signed"
       assert_equal "signed cookie".inspect, last_response.body
 
       get "/foo/read_raw_cookie"
-      assert_equal "signed cookie", verifier_sha512.verify(last_response.body)
+      assert_equal "signed cookie", verifier_sha512.verify(last_response.body, purpose: "cookie.signed_cookie")
     end
 
     test "encrypted cookies rotating multiple encryption keys" do
@@ -180,14 +180,14 @@ module ApplicationTests
       assert_equal "encrypted cookie".inspect, last_response.body
 
       get "/foo/read_raw_cookie"
-      assert_equal "encrypted cookie", encryptor.decrypt_and_verify(last_response.body)
+      assert_equal "encrypted cookie", encryptor.decrypt_and_verify(last_response.body, purpose: "cookie.encrypted_cookie")
 
-      get "/foo/write_raw_cookie_sha256"
+      get "/foo/write_raw_cookie_two"
       get "/foo/read_encrypted"
       assert_equal "encrypted cookie".inspect, last_response.body
 
       get "/foo/read_raw_cookie"
-      assert_equal "encrypted cookie", encryptor.decrypt_and_verify(last_response.body)
+      assert_equal "encrypted cookie", encryptor.decrypt_and_verify(last_response.body, purpose: "cookie.encrypted_cookie")
     end
   end
 end
diff --git a/railties/test/application/middleware/session_test.rb b/railties/test/application/middleware/session_test.rb
index 9182a63ab7..b25e56b625 100644
--- a/railties/test/application/middleware/session_test.rb
+++ b/railties/test/application/middleware/session_test.rb
@@ -183,7 +183,7 @@ module ApplicationTests
       encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
 
       get "/foo/read_raw_cookie"
-      assert_equal 1, encryptor.decrypt_and_verify(last_response.body)["foo"]
+      assert_equal 1, encryptor.decrypt_and_verify(last_response.body, purpose: "cookie._myapp_session")["foo"]
     end
 
     test "session upgrading signature to encryption cookie store works the same way as encrypted cookie store" do
@@ -235,7 +235,7 @@ module ApplicationTests
       encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
 
       get "/foo/read_raw_cookie"
-      assert_equal 1, encryptor.decrypt_and_verify(last_response.body)["foo"]
+      assert_equal 1, encryptor.decrypt_and_verify(last_response.body, purpose: "cookie._myapp_session")["foo"]
     end
 
     test "session upgrading signature to encryption cookie store upgrades session to encrypted mode" do
@@ -297,7 +297,7 @@ module ApplicationTests
       encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
 
       get "/foo/read_raw_cookie"
-      assert_equal 2, encryptor.decrypt_and_verify(last_response.body)["foo"]
+      assert_equal 2, encryptor.decrypt_and_verify(last_response.body, purpose: "cookie._myapp_session")["foo"]
     end
 
     test "session upgrading from AES-CBC-HMAC encryption to AES-GCM encryption" do
@@ -364,7 +364,7 @@ module ApplicationTests
         encryptor = ActiveSupport::MessageEncryptor.new(secret[0, ActiveSupport::MessageEncryptor.key_len(cipher)], cipher: cipher)
 
         get "/foo/read_raw_cookie"
-        assert_equal 2, encryptor.decrypt_and_verify(last_response.body)["foo"]
+        assert_equal 2, encryptor.decrypt_and_verify(last_response.body, purpose: "cookie._myapp_session")["foo"]
       ensure
         ENV["RAILS_ENV"] = old_rails_env
       end
@@ -428,7 +428,7 @@ module ApplicationTests
         verifier = ActiveSupport::MessageVerifier.new(app.secrets.secret_token)
 
         get "/foo/read_raw_cookie"
-        assert_equal 2, verifier.verify(last_response.body)["foo"]
+        assert_equal 2, verifier.verify(last_response.body, purpose: "cookie._myapp_session")["foo"]
       ensure
         ENV["RAILS_ENV"] = old_rails_env
       end