After MyBios (Mebromi) became the first malware to successfully infect the Award BIOS and survive a reboot to own the system, BIOS-based rootkits became the toast of the malware research community. That was in 2011, and now, months after the initial discovery, McAfee has found another BIOS-based rootkit – BIOSkit.
McAfee’s Arvind Gowda detailed the discovery on the company’s blog, the main attack starts with a DLL file that infects the Master Boot Record (MBR). It overwrites the original MBR and writes the file to be dropped (the downloader) in hidden sectors. After this, the DLL copies itself to the Recycle folder and deletes itself, Gowda explained.
The downloader is dropped and executed every time the system is started.
“The sys file responsible for flashing the BIOS is similar to the one seen in MyBios. Unlike bios.sys, the code to check the BIOS manufacturer and the BIOS size is present in the DriverEntry. However, the functionality of both the drivers remains the same,” he wrote.
“We have now seen two Bioskit malware in the wild within a couple of months. When the first Bioskit was identified, we did not know how soon we would see another.”
Based on the discovery, McAfee expects to see more examples of BIOS-based rootkits in the future. While detecting and cleaning infections to the MBR isn’t hard for a security company, cleaning BIOS infections presents a separate challenge altogether. Should a security firm make an error in the infection removal process within the BIOS, they could turn an expensive system into a rather expensive brick.