The (1) do_send and (2) do_recv functions in io.c in libvchan in Xen 4.2.x, 4.3.x, and 4.4-RC series allows local guests to cause a denial of service or possibly gain privileges via crafted xenstore ring indexes, which triggers a "read or write past the end of the ring."
Improper Input Validation 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.