This vulnerability affects the Mercusys AC12G (EU) V1 router running firmware AC12G(EU)_V1_200909. The router's UPnP IGD service on port 1900 exposes 15 out of 18 actions without requiring authentication, including sensitive functions like AddPortMapping and GetExternalIPAddress. Since UPnP is enabled by default via the admin interface, any device on the local network can exploit this to manipulate port forwarding rules and retrieve WAN traffic data without credentials.

An attacker with access to the local network can create arbitrary port forwarding rules, potentially exposing internal services to the internet or redirecting traffic. They can also obtain WAN traffic statistics, which may aid in further reconnaissance. This compromises the router's network configuration integrity and privacy of WAN usage data. There is no indication of remote exploitation from outside the LAN or known exploits in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, it is recommended to disable UPnP on the router if possible or restrict LAN device access to the router's management interface to trusted devices only. Monitor vendor communications for updates on patches or firmware upgrades addressing this issue.