I did not know this.
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Schneier on Security: The Eavesdropping System in Your Computer
Dan Farmer has an interesting paper (long version here; short version here) discussing the Baseboard Management Controller on your computer's motherboard:The BMC is an embedded computer found on most server motherboards made in the last 10 or 15 years. Often running Linux, the BMC's CPU, memory, storage, and network run independently. It runs Intel's IPMI out-of-band systems management protocol alongside network services (web, telnet, VNC, SMTP, etc.) to help manage, debug, monitor, reboot, and roll out servers, virtual systems, and supercomputers. Vendors frequently add features and rebrand OEM'd BMCs: Dell has iDRAC, Hewlett Packard iLO, IBM calls theirs IMM2, etc. It is popular because it helps raise efficiency and lower costs associated with availability, personnel, scaling, power, cooling, and more.
To do its magic, the BMC has near complete control over the server's hardware: the IPMI specification says that it can have "full access to system memory and I/O space." Designed to operate when the bits hit the fan, it continues to run even if the server is powered down. Activity on the BMC is essentially invisible unless you have a good hardware hacker on your side or have cracked root on the embedded operating system.
What's the problem?
There is a constant tradeoff between convenience and security.