The subpage MMIO initialization functionality in the subpage_register function in exec.c in QEMU-KVM, as used in the Hypervisor (aka rhev-hypervisor) in Red Hat Enterprise Virtualization (RHEV) 2.2 and KVM 83, does not properly select the index for access to the callback array, which allows guest OS users to cause a denial of service (guest OS crash) or possibly gain privileges via unspecified vectors.