Microsoft has fixed a security feature bypass vulnerability in Secure Boot that allows attackers to compromise the operating system s booting process even when Secure Boot is enabled. The vulnerability has a publicly available exploit code that works during most exploitation attempts which require running a specially crafted application. Rootkits can be used by threat actors to inject malicious code into a computer’s UEFI firmware, to replace the OS’s bootloader, or to replace parts of the Windows kernel. Microsoft also released guidance for applying Secure Boot DBX updates after the disclosure of the BootHole GRUB bootloader vulnerability in July 2020.
Source: https://www.bleepingcomputer.com/news/security/microsoft-fixes-secure-boot-bug-allowing-windows-rootkit-installation/