Mercusys AC12G (EU) V1 router with firmware AC12G(EU)_V1_200909 contains a vulnerability that exposes 128 bytes of uninitialized buffer memory when processing POST requests without SOAPAction header on UPnP port 1900. This memory disclosure vulnerability can be exploited by unauthenticated attackers on adjacent networks, potentially revealing sensitive internal memory contents. The vulnerability affects the UPnP service implementation and requires no authentication to exploit.