Microsoft » Windows Xp : Security Vulnerabilities, CVEs, Published In October 2011 (Denial of service)

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 validate user-mode input, which allows local users to gain privileges or cause a denial of service (NULL pointer dereference and system crash) via a crafted application, aka "Win32k Null Pointer De-reference Vulnerability."