Merge branch 'security-deny-implicit-confidential' into 'master'

Deny implicit flow for confidential apps

See merge request gitlab-org/security/gitlab!1164

app/controllers/oauth/authorizations_controller.rb

@@ -4,7 +4,7 @@ class Oauth::AuthorizationsController < Doorkeeper::AuthorizationsController
   include Gitlab::Experimentation::ControllerConcern
   include InitializesCurrentUserMode
 
-  before_action :verify_confirmed_email!
+  before_action :verify_confirmed_email!, :verify_confidential_application!
 
   layout 'profile'
 
@@ -24,18 +24,19 @@ class Oauth::AuthorizationsController < Doorkeeper::AuthorizationsController
     end
   end
 
-  def create
-    # Confidential apps require the client_secret to be sent with the request.
-    # Doorkeeper allows implicit grant flow requests (response_type=token) to
-    # work without client_secret regardless of the confidential setting.
-    if pre_auth.authorizable? && pre_auth.response_type == 'token' && pre_auth.client.application.confidential
-      render "doorkeeper/authorizations/error"
-    else
-      super
-    end
+  private
+
+  # Confidential apps require the client_secret to be sent with the request.
+  # Doorkeeper allows implicit grant flow requests (response_type=token) to
+  # work without client_secret regardless of the confidential setting.
+  # This leads to security vulnerabilities and we want to block it.
+  def verify_confidential_application!
+    render 'doorkeeper/authorizations/error' if authorizable_confidential?
   end
 
-  private
+  def authorizable_confidential?
+    pre_auth.authorizable? && pre_auth.response_type == 'token' && pre_auth.client.application.confidential
+  end
 
   def verify_confirmed_email!
     return if current_user&.confirmed?

changelogs/unreleased/security-deny-implicit-confidential.yml

+---
+title: Deny implicit flow for confidential apps
+merge_request:
+author:
+type: security

spec/controllers/oauth/authorizations_controller_spec.rb

@@ -51,10 +51,27 @@ RSpec.describe Oauth::AuthorizationsController do
     end
   end
 
+  shared_examples "Implicit grant can't be used in confidential application" do
+    context 'when application is confidential' do
+      before do
+        application.update(confidential: true)
+        params[:response_type] = 'token'
+      end
+
+      it 'does not allow the implicit flow' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(response).to render_template('doorkeeper/authorizations/error')
+      end
+    end
+  end
+
   describe 'GET #new' do
     subject { get :new, params: params }
 
     include_examples 'OAuth Authorizations require confirmed user'
+    include_examples "Implicit grant can't be used in confidential application"
 
     context 'when the user is confirmed' do
       let(:confirmed_at) { 1.hour.ago }
@@ -95,26 +112,14 @@ RSpec.describe Oauth::AuthorizationsController do
     subject { post :create, params: params }
 
     include_examples 'OAuth Authorizations require confirmed user'
-
-    context 'when application is confidential' do
-      before do
-        application.update(confidential: true)
-        params[:response_type] = 'token'
-      end
-
-      it 'does not allow the implicit flow' do
-        subject
-
-        expect(response).to have_gitlab_http_status(:ok)
-        expect(response).to render_template('doorkeeper/authorizations/error')
-      end
-    end
+    include_examples "Implicit grant can't be used in confidential application"
   end
 
   describe 'DELETE #destroy' do
     subject { delete :destroy, params: params }
 
     include_examples 'OAuth Authorizations require confirmed user'
+    include_examples "Implicit grant can't be used in confidential application"
   end
 
   it 'includes Two-factor enforcement concern' do