An annoying vulnerability in the widely used GRUB2 bootloader can be potentially exploited by malware or a rogue insider already on a machine to thoroughly compromise the operating system or hypervisor while evading detection by users and security tools.
Designated CVE-2020-10713, the vulnerability allows a miscreant to achieve code execution within the open-source bootloader, and effectively control the device at a level above the firmware and below any system software. Bug hunters at Eclypsium, who found the flaw and dubbed it BootHole, said patching the programming blunder will be a priority and a headache for admins.
To be clear, malware or a rogue user must already have administrator privileges on the device to exploit the flaw, which for the vast majority of victims is a game-over situation anyway. You’ve likely lost all your data and network integrity at that point. What this bootloader bug opens up is the ability for a determined miscreant to burrow deeper, run code at a low level below other defenses, and compromise the foundation of a system to the point where they cannot be easily detected by administrators nor antivirus.