Restrict slash commands to users who can log in

app/models/project_services/slash_commands_service.rb

@@ -35,6 +35,8 @@ class SlashCommandsService < Service
     chat_user = find_chat_user(params)
     if chat_user&.user
+      return Gitlab::SlashCommands::Presenters::Access.new.access_denied unless chat_user.user.can?(:use_slash_commands)
+
       Gitlab::SlashCommands::Command.new(project, chat_user, params).execute
     else
       url = authorize_chat_name_url(params)

app/policies/global_policy.rb

@@ -37,6 +37,7 @@ class GlobalPolicy < BasePolicy
     enable :access_git
     enable :receive_notifications
     enable :use_quick_actions
+    enable :use_slash_commands
   end
   rule { blocked | internal }.policy do
@@ -44,6 +45,7 @@ class GlobalPolicy < BasePolicy
     prevent :access_api
     prevent :access_git
     prevent :receive_notifications
+    prevent :use_slash_commands
   end
   rule { required_terms_not_accepted }.policy do
@@ -61,6 +63,7 @@ class GlobalPolicy < BasePolicy
   rule { access_locked }.policy do
     prevent :log_in
+    prevent :use_slash_commands
   end
   rule { ~(anonymous & restricted_public_level) }.policy do

changelogs/unreleased/security-2873-blocked-user-slash-command-bypass-master.yml

+---
+title: Restrict slash commands to users who can log in
+merge_request:
+author:
+type: security

spec/policies/global_policy_spec.rb

@@ -226,4 +226,32 @@ describe GlobalPolicy do
       it { is_expected.not_to be_allowed(:read_instance_statistics) }
     end
   end
+
+  describe 'slash commands' do
+    context 'regular user' do
+      it { is_expected.to be_allowed(:use_slash_commands) }
+    end
+
+    context 'when internal' do
+      let(:current_user) { User.ghost }
+
+      it { is_expected.not_to be_allowed(:use_slash_commands) }
+    end
+
+    context 'when blocked' do
+      before do
+        current_user.block
+      end
+
+      it { is_expected.not_to be_allowed(:use_slash_commands) }
+    end
+
+    context 'when access locked' do
+      before do
+        current_user.lock_access!
+      end
+
+      it { is_expected.not_to be_allowed(:use_slash_commands) }
+    end
+  end
 end

spec/support/shared_examples/chat_slash_commands_shared_examples.rb

@@ -91,6 +91,19 @@ RSpec.shared_examples 'chat slash commands service' do
           subject.trigger(params)
         end
+
+        context 'when user is blocked' do
+          before do
+            chat_name.user.block
+          end
+
+          it 'blocks command execution' do
+            expect_any_instance_of(Gitlab::SlashCommands::Command).not_to receive(:execute)
+
+            result = subject.trigger(params)
+            expect(result).to include(text: /^Whoops! This action is not allowed/)
+          end
+        end
       end
     end
   end