The PV domain builder in Xen 4.2 and earlier does not validate the size of the kernel or ramdisk (1) before or (2) after decompression, which allows local guest administrators to cause a denial of service (domain 0 memory consumption) via a crafted (a) kernel or (b) ramdisk.
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.