The get_page_type function in xen/arch/x86/mm.c in Xen 4.2, when debugging is enabled, allows local PV or HVM guest administrators to cause a denial of service (assertion failure and hypervisor crash) via unspecified vectors related to a hypercall.
https://exchange.xforce.ibmcloud.com/vulnerabilities/80977
http://www.securitytracker.com/id?1027937
http://www.securityfocus.com/bid/57159
http://www.openwall.com/lists/oss-security/2013/01/04/2
http://security.gentoo.org/glsa/glsa-201309-24.xml
http://secunia.com/advisories/55082
http://seclists.org/oss-sec/2013/q1/att-17/xsa37-4_2.patch
http://lists.opensuse.org/opensuse-updates/2013-04/msg00052.html
http://lists.opensuse.org/opensuse-updates/2013-04/msg00051.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00021.html