HGFS.sys in the VMware Tools package in VMware Workstation 5.x before 5.5.6 build 80404, VMware Player before 1.0.6 build 80404, VMware ACE before 1.0.5 build 79846, VMware Server before 1.0.5 build 80187, and VMware ESX 2.5.4 through 3.0.2 does not properly validate arguments in user-mode METHOD_NEITHER IOCTLs to the \\.\hgfs device, which allows guest OS users to modify arbitrary memory locations in guest kernel memory and gain privileges.