The instruction decoder in arch/x86/kvm/emulate.c in the KVM subsystem in the Linux kernel before 3.18-rc2 does not properly handle invalid instructions, which allows guest OS users to cause a denial of service (NULL pointer dereference and host OS crash) via a crafted application that triggers (1) an improperly fetched instruction or (2) an instruction that occupies too many bytes. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-8480.
https://bugzilla.redhat.com/show_bug.cgi?id=1156615
http://thread.gmane.org/gmane.comp.emulators.kvm.devel/128427