Microsoft Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, and Windows 10 Gold and 1511 allow attackers to bypass the Secure Boot protection mechanism by leveraging (1) administrative or (2) physical access to install a crafted boot manager, aka "Secure Boot Security Feature Bypass."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-100