Microsoft has identified three UEFI bootloads that can bypass the Windows Secure Boot feature and execute unsigned code.
Secure Boot is part of the UEFI specification, which is designed to ensure that only trust code signed with a specific certificate supplied by the manufacturer is executed to start the boot process of the operating system.
The three Microsoft-approved bootloads include New Horizon Datasys (CVE-2022-34302: bypass Secure Boot via custom installer), CryptoPro Secure Disk (CVE-2022-34301: bypass Secure Boot via UEFI Shell execution) and Eurosoft (UK) (CVE-2022-34303: bypass Secure Boot via UEFI Shell execution).
Microsoft has worked with the last two vendors in the above list to release security update KB5012170 to fix the issue in the provided bootloader. Microsoft also blocked all required certificates issued with the July 2022 security update release.
The signed third-party bootloaders for the Unified Extensible Firmware Interface (UEFI) could allow attackers to execute unauthorized code at an early stage of the boot process before the operating system is loaded.
Threat actors could exploit the vulnerability to create persistence on a target system that cannot be removed by reinstalling the operating system.
Vulnerabilities in UEFI bootloaders were discovered by Eclypsium security researchers Mickey Shkatov and Jesse Michael.
The sources for this piece include an article in BleepingComputer.