hcmon.sys in VMware Workstation 6.5.1 and earlier, VMware Player 2.5.1 and earlier, VMware ACE 2.5.1 and earlier, and VMware Server 1.0.x before 1.0.9 build 156507 and 2.0.x before 2.0.1 build 156745 uses the METHOD_NEITHER communication method for IOCTLs, which allows local users to cause a denial of service via a crafted IOCTL request.