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.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.