Fix access to pages domain settings

app/controllers/projects/pages_domains_controller.rb

@@ -4,7 +4,7 @@ class Projects::PagesDomainsController < Projects::ApplicationController
   layout 'project_settings'
 
   before_action :require_pages_enabled!
-  before_action :authorize_update_pages!, except: [:show]
+  before_action :authorize_update_pages!
   before_action :domain, except: [:new, :create]
 
   def show

changelogs/unreleased/54850-pages-domain-show-view-is-not-protected-by-access-control.yml

+---
+title: Require maintainer access to show pages domain settings
+merge_request: 24926
+author:
+type: fixed

spec/controllers/projects/pages_domains_controller_spec.rb

@@ -23,12 +23,27 @@ describe Projects::PagesDomainsController do
   end
 
   describe 'GET show' do
-    it "displays the 'show' page" do
+    def make_request
       get(:show, params: request_params.merge(id: pages_domain.domain))
+    end
 
+    it "displays the 'show' page" do
+      make_request
       expect(response).to have_gitlab_http_status(200)
       expect(response).to render_template('show')
     end
+
+    context 'when user is developer' do
+      before do
+        project.add_developer(user)
+      end
+
+      it 'renders 404 page' do
+        make_request
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
   end
 
   describe 'GET new' do