By I. D. Pankov, A. S. Konoplev & A. Yu. Chernov
The paper presents an overview of current attacks on BIOS and Intel ME embedded software of modern Intel-based computers. We describe the results of the analysis of its security for system boards of basic manufacturers. We also allocate classes of attacks that make it possible to create implants whose discovery by traditional methods of searching for undeclared features becomes impossible or extremely difficult.[…]
It costs US$40, I don’t know of a freely-available version of this paper. I wish Aaron Swartz was still alive. 😦
https://link.springer.com/article/10.3103%2FS0146411619080224
Firmware Security 