Memory leak in Xen 4.2 and unstable allows local HVM guests to cause a denial of service (host memory consumption) by performing nested virtualization in a way that triggers errors that are not properly handled.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2013-0195
http://www.securitytracker.com/id/1028032
http://www.openwall.com/lists/oss-security/2013/01/23/8