Safer Boots: Feds Urge Malware-Resistant BIOS

11 Security Sights Seen Only At Black Hat

Memo to manufacturers: Improve the security of the BIOS ROM chip flashware running on PCs and servers.

That's the gist of a recently released draft report from the National Institute of Standards and Technology (NIST), which offers advice on how manufacturers can better protect the BIOS flashware used on servers. NIST currently is soliciting comments on the draft report, which can be filed with the agency until Sept. 14, 2012.

Why worry about the BIOS? "Unauthorized modification of BIOS firmware by malicious software constitutes a significant threat because of the BIOS's unique and privileged position within the PC architecture. Malicious BIOS modification could be part of a sophisticated, targeted attack on an organization--either a permanent denial of service or a persistent malware presence," says the report.

Previous examples of BIOS-infecting malware are relatively rare, but include the Windows-targeting CIH or Chernobyl virus, which appeared in 1998 and could flash a BIOS and corrupt it, after erasing the data on a PC.

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But worries over BIOS security have been growing, especially since researchers in 2009 demonstrated a technique for injecting code into any unsigned firmware. Last year, security researchers discovered a BIOS-altering rootkit called Mebromi, which can alter boot-time instructions in the BIOS, which in turn alter the computer's master boot record (MBR). When the PC powers on, firmware in the BIOS ROM loads and executes the MBR, which is the sector at the very beginning of a hard drive, and thus the first to load.

Infecting the BIOS and MBR makes it difficult for antivirus software to find or eradicate the malware, raising the possibility that attackers could create boot-proof and antivirus-resistant rootkits.

"Developing an antivirus utility able to clean the BIOS code is a challenge, because it needs to be totally error-proof, to avoid rendering the system unbootable at all," said Webroot security researcher Marco Giuliani last year, in his analysis of Mebroni. In fact, even small coding errors made when trying to repair a BIOS could brick the machine. On the upside, however, in the case of Mebroni, the malware could only infect PCs with a BIOS ROM made by Award, which is part of Phoenix.

As Mebroni demonstrates, servers aren't the only systems at risk from a BIOS attack. Last year, NIST released "BIOS Protection Guidelines" for PC manufacturers, to help them prevent unwanted BIOS modification on PCs by attackers.

The report warned that BIOS implementations could become more susceptible to such attacks in the future. "The move from conventional BIOS implementations to implementations based on the Unified Extensible Firmware Interface (UEFI) may make it easier for malware to target the BIOS in a widespread fashion, as these BIOS implementations are based on a common specification," it said, meaning that attackers could potentially hit more targets at once with a single piece of malware.

Accordingly, NIST recommends that manufacturers begin cryptographically signing their BIOS updates, and treating the BIOS as an essential part of PC security. "By building security into the firmware, you establish the foundation for a secure system," report co-author Andrew Regenscheid told ScienceDaily.

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