win32k.sys in the kernel-mode drivers in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP2, Windows Server 2008 SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly handle window messaging, which allows local users to gain privileges via a crafted application that calls the PostMessage function, aka "PostMessage Function Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A14217
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2012/ms12-018