Let's start with the theory: if you have access to the television, you should be able to install your own custom firmware. Then there's the HDMI constraint; HD

Let's start with the theory: if you have access to the television, you should be able to install your own custom firmware. Then there's the HDMI constraint; HDMI is a bidirectional interface by design, and while it looks nice, it's built for packet streams rather than data blocks. From a user's perspective, this is a dead-end; however, for a hacker, there must be a way to wrap data blocks into packet streams; especially since the HDMI port/cable does transfer data from PC to TV, such as information about the movie you're watching, time left, and so on, in addition to commands and selections from TV to PC, this is known as HDMI-CEC (Consumer Electronics Control), and there is also the HDMI-HEC (High-speed Ethernet Channel) which provides internet sharing for devices connected with the HDMI cable. So yes, it's a possible threat vector as is everything nowadays. Does it fit inside your cybersecurity threat scenario/risk scheme? Up to you to decide.