According to the Kaspersky researchers who discovered it, a new firmware bootkit discovered in the wild demonstrates remarkable advances over previous similar tools. MoonBounce is a harmful implant that hides in a computer's UEFI firmware in the system's SPI flash - a storage component external to the hard drive, making it difficult to remove and difficult for proprietary security products to detect. UEFI is a technical specification that aids in the interoperability of computer systems' operating systems (OS) and firmware software.
Being able to place malicious code known as a "UEFI bootkit" in the firmware is an ideal approach to avoid detection by antivirus software and other security measures running at the OS level. This has been done before, with the FinFisher malware and the ESPecter backdoor being two recent instances. In general, these tools hijack the boot sequence and initialize it before the operating system's security components. They are extremely tenacious because they nest in regions that cannot be wiped, such as reserved disk space.
"The source of the infection starts with a set of hooks that intercept the execution of several functions in the EFI Boot Services Table, namely AllocatePool, CreateEventEx, and ExitBootServices," explains Kaspersky in the report. "Those hooks are used to divert the flow of these functions to malicious shellcode that is appended by the attackers to the CORE_DXE image, which in turn sets up additional hooks in subsequent components of the boot chain, namely the Windows loader."
MoonBounce is the third bootkit identified in the wild, following LoJax and MosaicRegressor, and it shows "substantial development, with a more sophisticated attack flow and better technical sophistication" when compared to predecessors. It was discovered in 2021 by Kaspersky using its Firmware Scanner, which is designed to detect threats hidden in the ROM BIOS, including UEFI firmware images.
Kaspersky discovered a plethora of evidence linking MoonBounce to APT41, ranging from the deployment of the ScrambleCross malware itself to unique certificates acquired from its C2 servers that correspond to earlier FBI reports on APT41 activities. While the United States Department of Justice discovered and charged five APT41 members in September 2020, the presence of MoonBounce and the operation around it demonstrates that the threat actors were not deterred by the legal pressure.
According to the telemetry data, the attacks were extremely targeted, and Kaspersky only detected the firmware rootkit on one occasion. Kaspersky discovered several malware samples and loaders in other devices on the same network, however, they were non-UEFI implants. Microcin backdoor, Mimikat credential stealer, Go implant, StealthMutant loader, and ScrambleCross malware are a few examples.
