Xen 4.2.x and 4.3.x, when nested virtualization is disabled, does not properly check the emulation paths for (1) VMLAUNCH and (2) VMRESUME, which allows local HVM guest users to cause a denial of service (host crash) via unspecified vectors related to "guest VMX instruction execution."
http://lists.opensuse.org/opensuse-updates/2013-12/msg00059.html
http://secunia.com/advisories/55398
http://security.gentoo.org/glsa/glsa-201407-03.xml
https://exchange.xforce.ibmcloud.com/vulnerabilities/88649