Firmware
Code built into the hardware that starts it and runs below the OS.
What It Is
Firmware is software built into the hardware, kept on a chip on the board, not on the disk. It is the first code to run when a machine powers on. UEFI, which replaced the older BIOS, checks and sets up the hardware and then starts the operating system's boot loader, the small program that loads the operating system.
Firmware is not part of the operating system, and wiping or replacing the disk does not remove it. Servers also carry a BMC (baseboard management controller), a small separate computer on the board with its own network port. It lets administrators manage the server remotely, even while it is switched off.
Firmware is updated far less often than the operating system, usually with the hardware maker's own tools, so it is easy to leave behind.
- App
- Framework
- Web Server
- Runtime
- Containers
- OS
- Hypervisor
- Firmware
- Hardware
- Data
On This Layer
These are the technologies on the Firmware layer that this topic covers. Open one to see what it runs on, how to spot it and what a flaw in it reaches.
How Far a Flaw Reaches
A flaw in firmware runs below the operating system and every security tool on it. Code planted there can survive a disk wipe and reinstall, and an exposed BMC gives control of the server over the network, close to standing in front of it.