Use safe redirect paths in admin redirects

app/controllers/alchemy/admin/base_controller.rb

@@ -31,6 +31,27 @@ def leave
 
       private
 
+      def safe_redirect_path(path = params[:redirect_to], fallback: admin_path)
+        if is_safe_redirect_path?(path)
+          path
+        elsif is_safe_redirect_path?(fallback)
+          fallback
+        else
+          admin_path
+        end
+      end
+
+      def is_safe_redirect_path?(path)
+        mount_path = alchemy.root_path
+        path.to_s.match? %r{^#{mount_path}admin/}
+      end
+
+      def relative_referer_path(referer = request.referer)
+        return unless referer
+
+        URI(referer).path
+      end
+
       # Disable layout rendering for xhr requests.
       def set_layout
         (request.xhr? || turbo_frame_request?) ? false : "alchemy/admin"
@@ -105,16 +126,23 @@ def render_errors_or_redirect(object, redirect_url, flash_notice)
         end
       end
 
-      # Does redirects for html and js requests
+      # Does redirects for html, turbo_stream and js requests
+      #
+      # Makes sure that the redirect path is safe.
       #
       def do_redirect_to(url_or_path)
+        redirect_path = safe_redirect_path(url_or_path)
         respond_to do |format|
           format.js do
-            @redirect_url = url_or_path
+            @redirect_url = redirect_path
             render :redirect
           end
-          format.turbo_stream { redirect_to(url_or_path) }
-          format.html { redirect_to(url_or_path) }
+          format.turbo_stream do
+            redirect_to(redirect_path, allow_other_host: false)
+          end
+          format.html do
+            redirect_to(redirect_path, allow_other_host: false)
+          end
         end
       end
 

app/controllers/alchemy/admin/languages_controller.rb

@@ -40,7 +40,7 @@ def destroy
       def switch
         @language = set_alchemy_language(params[:language_id])
         session[:alchemy_language_id] = @language.id
-        do_redirect_to request.referer || alchemy.admin_dashboard_path
+        do_redirect_to relative_referer_path || alchemy.admin_dashboard_path
       end
 
       private

app/controllers/alchemy/admin/pages_controller.rb

@@ -187,17 +187,13 @@
         respond_to do |format|
           format.js
           format.html do
             redirect_to(unlock_redirect_path, allow_other_host: true)
           end
         end
       end
 
       def unlock_redirect_path
-        if params[:redirect_to].to_s.match?(/\A\/admin\/(layout_)?pages/)
-          params[:redirect_to]
-        else
-          admin_pages_path
-        end
+        safe_redirect_path(fallback: admin_pages_path)
       end
 
       # Sets the page public and updates the published_at attribute that is used as cache_key

app/controllers/alchemy/admin/resources_controller.rb

@@ -78,7 +78,7 @@ def destroy
           flash[:error] = resource_instance_variable.errors.full_messages.join(", ")
         end
         flash_notice_for_resource_action
-        do_redirect_to resource_url_proxy.url_for(search_filter_params.merge(action: "index"))
+        do_redirect_to resource_url_proxy.url_for(search_filter_params.merge(action: "index", only_path: true))
       end
 
       def resource_handler

spec/controllers/alchemy/admin/base_controller_spec.rb

@@ -211,4 +211,132 @@ def index
       end
     end
   end
+
+  describe "#safe_redirect_path" do
+    subject { controller.send(:safe_redirect_path) }
+
+    context "when params[:redirect_to] is present" do
+      before do
+        allow(controller).to receive(:params) { {redirect_to: redirect_url} }
+      end
+
+      context "and it is not an external URL" do
+        let(:redirect_url) { "/admin/pages" }
+
+        it "redirects to given path" do
+          is_expected.to eq("/admin/pages")
+        end
+      end
+
+      context "and it is an external URL" do
+        let(:redirect_url) { "https://evil.com" }
+
+        context "and no fallback is given" do
+          it "redirects to default fallback path" do
+            is_expected.to eq("/admin")
+          end
+        end
+
+        context "and a fallback is given" do
+          subject { controller.send(:safe_redirect_path, fallback: "/admin/pages") }
+
+          context "which is a safe path" do
+            it "redirects to given fallback path" do
+              is_expected.to eq("/admin/pages")
+            end
+          end
+
+          context "which is not a safe path" do
+            subject { controller.send(:safe_redirect_path, fallback: "evil.com") }
+
+            it "redirects to default fallback path" do
+              is_expected.to eq("/admin")
+            end
+          end
+        end
+      end
+    end
+
+    context "when params[:redirect_to] is not present" do
+      context "and another path is given" do
+        subject { controller.send(:safe_redirect_path, redirect_path) }
+
+        context "which is a safe path" do
+          let(:redirect_path) { "/admin/pages" }
+
+          it "redirects to given path" do
+            is_expected.to eq("/admin/pages")
+          end
+        end
+
+        context "which is not a safe path" do
+          let(:redirect_path) { "evil.com" }
+
+          it "redirects to default fallback path" do
+            is_expected.to eq("/admin")
+          end
+        end
+      end
+
+      context "and no fallback is given" do
+        it "redirects to default fallback path" do
+          is_expected.to eq("/admin")
+        end
+      end
+
+      context "and a fallback is given" do
+        subject { controller.send(:safe_redirect_path, fallback: "/admin/pages") }
+
+        context "which is a safe path" do
+          it "redirects to given fallback path" do
+            is_expected.to eq("/admin/pages")
+          end
+        end
+
+        context "which is not a safe path" do
+          subject { controller.send(:safe_redirect_path, fallback: "evil.com") }
+
+          it "redirects to default fallback path" do
+            is_expected.to eq("/admin")
+          end
+        end
+      end
+    end
+  end
+
+  describe "#is_safe_redirect_path?" do
+    subject { controller.send(:is_safe_redirect_path?, path) }
+
+    context "path is not an external URL" do
+      let(:path) { "/admin/pages" }
+
+      it { is_expected.to be(true) }
+    end
+
+    context "path is an external URL" do
+      let(:path) { "https://evil.com" }
+
+      it { is_expected.to be(false) }
+    end
+
+    context "alchemy is mounted under a path" do
+      before do
+        allow(controller).to receive(:alchemy) do
+          double(root_path: "/cms/")
+        end
+      end
+
+      context "path is not an external URL" do
+        let(:path) { "/cms/admin/pages" }
+
+        it { is_expected.to be(true) }
+      end
+
+      context "path is an external URL" do
+        let(:path) { "https://evil.com" }
+
+        it { is_expected.to be(false) }
+      end
+    end
+  end
 end