Malware in UEFI bios from the master?

Question

BIOS

Hello. Can a repairman sew a virus into UEFI bios and how to calculate it? What is the best thing to do when connecting a hard drive for the first time? Will flashing the bios from under Windows help if I put the types on a clean ssd (not needed) and flash the official bios from under it (for prevention). It seems that you can flash the BIOS from a flash drive from under the BIOS, I don’t remember, it seems that there is such a function on my motherboard.

Answer 1

secure boot, by the way, should protect against such actions, but yes, changing the logic of the BIOS behavior is quite possible, but I'm afraid this attack is very expensive and not available to simple repairmen (more precisely, the trojan itself should be quite complex and be a hypervisor that implements uefi loading already inside yourself)
with legasy boot mbr, placing such a trojan is easier,
ps in any case, small repairmen in such a situation are much more trusted than, for example, a large network

Answer 2

If there is a necessary skill, then it is possible with some probability.
The main question is, why the hell is this repairman

Answer 3

Yes, this is possible on some motherboards/platforms. Implants in UEFI from professional hack groups are an everyday reality. Many of them support firmware updates, so in order to reliably remove them, you need to flash the flash memory with a programmer, and not with the built-in update tools.