diff --git a/data/web/inc/ajax/container_ctrl.php b/data/web/inc/ajax/container_ctrl.php
index f0e220f9c..48c21cb13 100644
--- a/data/web/inc/ajax/container_ctrl.php
+++ b/data/web/inc/ajax/container_ctrl.php
@@ -1,4 +1,11 @@
 <?php
+
+// Block requests by checking the 'Sec-Fetch-Dest' header.
+if (isset($_SERVER['HTTP_SEC_FETCH_DEST']) && $_SERVER['HTTP_SEC_FETCH_DEST'] !== 'empty') {
+  header('HTTP/1.1 403 Forbidden');
+  exit;
+}
+
 require_once $_SERVER['DOCUMENT_ROOT'] . '/inc/prerequisites.inc.php';
 if (!isset($_SESSION['mailcow_cc_role']) || $_SESSION['mailcow_cc_role'] != 'admin') {
 	exit();