Hisense VIDAA Smart TV MQTT Broker Authentication Bypass

Hisense VIDAA Smart TV firmware V0000.01.00a.P0220 contains an authentication bypass vulnerability in its remote-control MQTT broker on TCP port 36669, which accepts publicly documented default credentials and an ineffective 4-digit pairing PIN with no rate limiting or lockout, allowing a brute force of the entire code space in about five seconds, while some actions require no pairing at all. A LAN-adjacent attacker can exploit this to inject key events, change volume, switch input sources, enumerate inputs, launch arbitrary installed applications, and monitor pairing activity, posing a significant risk in hotel deployments where untrusted LAN access is common.