Except... a key word in the article makes the hack perfectly believable and feasible: "baseboard management controller". If the chip is inserted on the serial

Except... a key word in the article makes the hack perfectly believable and feasible: "baseboard management controller". If the chip is inserted on the serial data line between the SPI flash memory and the BMC CPU, then, as an ex-InfoSec engineer, the whole thing sounds very plausible and even easy IMHO... You have to expect that any article about intricate tech details written for a general audience will get parts of their descriptions wrong. Like you I was raising my eyebrows when I started reading. But when they mentioned the BMC, I believed. The author did not make a vague mistake when mentioning this very specific technical term. In fact, the BMC is the perfect target for such a hardware hack: low-speed SPI flash memory interface easy to man-in-the-middle, BMC more privileged than the OS (can virtualize storage, keyboard, etc), BMC code independent of the OS (infect both Linux and Windows at once), BMC code changes so rarely that a backdoor making assumptions about the code layout and content would still work after many years of updates, etc. Edit: I checked Supermicro servers from the 2015 era. Most used the AST2400 BMC. It boots from SPI flash so this backdoor chip only has to intercept and modify bytes on the data out (DO) line to inject malicious code.