The process-initialization implementation in win32k.sys in the kernel-mode drivers in Microsoft Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, and Windows 10 does not properly constrain impersonation levels, which allows local users to gain privileges via a crafted application, aka "Win32k Elevation of Privilege Vulnerability."
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2015/ms15-097