Qemu, as used in Xen 4.0, 4.1 and possibly other products, when emulating certain devices with a virtual console backend, allows local OS guest users to gain privileges via a crafted escape VT100 sequence that triggers the overwrite of a "device model's address space."
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.