The Hyper-V server implementation in Microsoft Windows Server 2008 Gold, SP2, and R2 on the x64 platform allows guest OS users to cause a denial of service (host OS hang) via a crafted application that executes a malformed series of machine instructions, aka "Hyper-V Instruction Set Validation Vulnerability."
Race condition in Microsoft Windows Server 2003 and Vista allows local users to cause a denial of service (crash or hang) via a multi-threaded application that makes many calls to UnhookWindowsHookEx while certain other desktop activity is occurring.