Do not delay. An attacker on your local network (malicious IoT device, infected PC) can root your router in seconds using public scripts.
Consider putting this device in Bridge Mode (check ISP if allowed) and using a modern OpenWrt/DD-WRT router behind it. The EMG3525-T50B is excellent as a modem/ONT bridge, but mediocre as a firewall. Have you found a newer firmware version for the T50B? Or run into a bricked device after an update? Drop a comment below. Zyxel Firmware Emg3525-t50b
If you are a subscriber to certain fiber optic broadband providers (particularly in the Asia-Pacific region, such as Taiwan’s CHT or HiNet), the chances are high that the white box sitting in your living room is a Zyxel EMG3525-T50B . This GPON/802.11ac wireless router is a workhorse for last-mile connectivity, but like all carrier-grade gear, its firmware is a double-edged sword. Do not delay