This increases the attack surface, and since the security of their implement in embedded devices is far from ideal, an attacker could exploit them and inject malicious code.
The HDMI firewall blocks all the additional features, and only allow the equipment to receive audio and video data.
It is based on the research of Pierre-Michel RICORDEL and José LOPES-ESTEVES from ANSSI/SDE/ST/LSF presented at the IT security conference [SSTIC 2021](https://sstic.org/2021/presentation/un_pare_feu_pour_le_hdmi/).
Now plug in the HDMI firewall in the monitor to be protected.
Connect the cable going to the untrusted device on the HDMI firewall.
Your equipment is now protected.
To re-write the EEPROM of the HDMI firewall in case you want to protect another monitor, you can re-disable write protection by putting a solder blob across the two pads marked WP.
By default, the 5V supplied by the monitor are forwarded to the device.
To further reduce the attack surface, you can disable this by cutting the trace between the two pads marked 5V.
The risk is that some monitors rely on this signal to detect when a device is plugged in.