From bleepingcomputer.com
Windows users who have installed a new KB5012170 security update for Secure Boot have encountered various issues, ranging from boots failing with BitLocker Recovery prompts to performance issues.
A UEFI bootloader loads immediately after a device is started and is responsible for launching the UEFI environment with the Secure Boot feature to allow only trusted code to be executed when starting the Windows booting process.
During the August 2022 Patch Tuesday, Microsoft released the standalone KB5012170 ‘Security update for Secure Boot DBX’ to resolve vulnerabilities found in various UEFI bootloaders that threat actors could use to bypass the Windows Secure Boot feature and execute unsigned code.