The researcher discovered a vulnerability in the Windows Update process that allowed them to downgrade critical system components, including DLLs, drivers, and the NT kernel. This enabled the attacker to bypass security measures like Secure Boot and expose previously patched vulnerabilities.  There are many ways to disable VBS, including Credential Guard and HVCI, even with UEFI locks, demonstrating the potential for significant security risks on fully patched Windows systems.

Source: GBHackers