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."
https://exchange.xforce.ibmcloud.com/vulnerabilities/88649
http://www.securitytracker.com/id/1029313
http://www.securityfocus.com/bid/63625
http://www.openwall.com/lists/oss-security/2013/11/11/1
http://security.gentoo.org/glsa/glsa-201407-03.xml
http://secunia.com/advisories/55398
http://lists.opensuse.org/opensuse-updates/2013-12/msg00059.html