Xen 4.2.x and 4.3.x, when using Intel VT-d and a PCI device has been assigned, does not clear the flag that suppresses IOMMU TLB flushes when unspecified errors occur, which causes the TLB entries to not be flushed and allows local guest administrators to cause a denial of service (host crash) or gain privileges via unspecified vectors.
http://www.securitytracker.com/id/1029468
http://www.openwall.com/lists/oss-security/2013/12/10/7
http://security.gentoo.org/glsa/glsa-201407-03.xml
http://secunia.com/advisories/55932
http://lists.xen.org/archives/html/xen-announce/2013-12/msg00002.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00011.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-December/125111.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-December/125081.html