Xen 4.0.2 through 4.0.4, 4.1.x, and 4.2.x allows local PV guest users to cause a denial of service (hypervisor crash) via certain bit combinations to the XSETBV instruction.
Debian Linux Security Advisory 3006-1 - Multiple security issues have been discovered in the Xen virtualisation solution which may result in information leaks or denial of service.