Cybersecurity researchers at Kaspersky have discovered a third known case of a firmware bootkit in the wild.

The kit, which made its first appearance in the wild in the spring of 2021, has been named MoonBounce. Researchers are confident that the campaign is the work of well-known Chinese-speaking advanced persistent threat (APT) actor APT41.

MoonBounce demonstrates a more complicated attack flow and greater technical sophistication than previously discovered bootkits LoJax and MosaicRegressor.

The malicious implant was found hiding inside the CORE_DXE component of the Unified Extensible Firmware Interface (UEFI) firmware. UEFI firmware is critical because its code is responsible for booting up a device and passing control to the software that loads the operating system (OS). 

Once MoonBounce’s components have made their way into the operating system, they reach out to a command & control server to retrieve further malicious payloads, which Kaspersky researchers could not retrieve.

The code to boot the device is stored in a non-volatile component external to the hard drive called the Serial Peripheral Interface (SPI) flash. 

Researchers said that Bootkits of this kind are extremely hard to detect because the code they target is located outside of the device’s hard drive in an area that most security solutions do not scan as standard. 

Firmware bootkits are also difficult to delete. They can’t be removed simply by reformatting a hard drive or reinstalling an OS because the code is launched before the operating system.

“The infection chain itself does not leave any traces on the hard drive, since its components operate in memory only, thus facilitating a fileless attack with a small footprint,” noted researchers. 

While investigating MoonBounce, researchers appeared to detect a link between the bootkit and Microcin malware used by the SixLittleMonkeys threat actor.

“While we can’t definitely connect the additional malware implants found during our research to MoonBounce specifically, it does appear as if some Chinese-speaking threat actors are sharing tools with one another to aid in their various campaigns; there especially seems to be a low confidence connection between MoonBounce and Microcin,” said Denis Legezo, senior security researcher with GReAT (Kaspersky’s Global Research and Analysis Team).