The memory-management implementation in the Virtual Machine Monitor (aka VMM or hypervisor) in Microsoft Virtual PC 2007 Gold and SP1, Virtual Server 2005 Gold and R2 SP1, and Windows Virtual PC does not properly restrict access from the guest OS to memory locations in the VMM work area, which allows context-dependent attackers to bypass certain anti-exploitation protection mechanisms on the guest OS via crafted input to a vulnerable application.  NOTE: the vendor reportedly found that only systems with an otherwise vulnerable application are affected, because "the memory areas accessible from the guest cannot be leveraged to achieve either remote code execution or elevation of privilege and ... no data from the host is exposed to the guest OS."