The MSI-X MMIO support in hw/pci/msix.c in QEMU (aka Quick Emulator) allows local guest OS privileged users to cause a denial of service (NULL pointer dereference and QEMU process crash) by leveraging failure to define the .write method.
http://lists.fedoraproject.org/pipermail/package-announce/2016-January/175380.html
https://bugzilla.redhat.com/show_bug.cgi?id=1291137
https://security.gentoo.org/glsa/201602-01