I am sure you heard about this China spy chip hacking on the server hardware level. It seems the hardware manufactures decided to leave a vulnerability on their motherboard which was for convenience. Read this article to see how it was to hack in like China did. I find it quite interesting how this vulnerability existed since 2013 but nothing was done to patch it!
The spy chip could have been placed electrically between the baseboard management controller (BMC) and its SPI flash or serial EEPROM storage containing the BMC’s firmware. Thus, when the BMC fetched and executed its code from this memory, the spy chip would intercept the signals and modify the bitstream to inject malicious code into the BMC processor, allowing its masters to control the BMC.