diff --git a/server/notification-providers/pushdeer.js b/server/notification-providers/pushdeer.js
index 428f44703..e39d61d61 100644
--- a/server/notification-providers/pushdeer.js
+++ b/server/notification-providers/pushdeer.js
@@ -11,7 +11,8 @@ class PushDeer extends NotificationProvider {
     async send(notification, msg, monitorJSON = null, heartbeatJSON = null) {
         const okMsg = "Sent Successfully.";
         const serverUrl = notification.pushdeerServer || "https://api2.pushdeer.com";
-        const url = `${serverUrl.trim().replace(/(?<!\/)\/*$/, "")}/message/push`;
+        // capture group below is nessesary to prevent an ReDOS-attack
+        const url = `${serverUrl.trim().replace(/([^\/])\/+$/, "$1")}/message/push`;
 
         let valid = msg != null && monitorJSON != null && heartbeatJSON != null;