BIOS Attack

A BIOS attack is an exploit that infects the BIOS with malicious code and is persistent through reboots and attempts to reflash the firmware.

The BIOS is the firmware that runs while a computer boots up. Originally, it was hard-coded and read-only (which was why it was called firmware). Manufacturers now use an erasable format, such as flash memory, to make BIOS updates easier. As an unintended result, however, the change also means that the BIOS is vulnerable to online attack.

A BIOS attack does not require any vulnerability on the target system. Once an attacker gains administrative-level privileges through some other mechanism, he can flash the BIOS over the Internet with malware-laden firmware. A BIOS attack could infect a decompression routine used in the majority of motherboards.

It was once thought that BIOS malware would have to be written specifically for each of the many different BIOS implementations. However, at the 2009 CanSecWest security conference, researchers Alfredo Ortega and Anibal Sacco demonstrated a generic BIOS attack that would enable full control of the underlying firmware, regardless of the operating system. That ability means that such an attack could be widespread and portable among platforms.

There are two methods of preventing BIOS infection. The first method involves physically setting the BIOS to make it non-writeable. The second method relies on a hardware cryptographic key burned into the BIOS chip at manufacture that can be used to verify that the code has not been modified.