Spoiler alert:
1) Malware and UEFI Rootkits
2) Exploiting Firmware Remotely
3) Physical Tampering
4) Management Backdoors
5) Supply Chain Attacks
Full blog post: https://eclypsium.com/2018/12/28/the-top-5-firmware-and-hardware-attack-vectors/
Whitepaper: https://eclypsium.com/wp-content/uploads/2018/12/Top-5-Firmware-Attack-Vectors.pdf