The do_physdev_op function in Xen 4.1.5, 4.1.6.1, 4.2.2 through 4.2.3, and 4.3.x does not properly restrict access to the (1) PHYSDEVOP_prepare_msix and (2) PHYSDEVOP_release_msix operations, which allows local PV guests to cause a denial of service (host or guest malfunction) or possibly gain privileges via unspecified vectors.
https://exchange.xforce.ibmcloud.com/vulnerabilities/90675
http://xenbits.xen.org/xsa/xsa87-unstable-4.3.patch
http://xenbits.xen.org/xsa/advisory-87.html
http://www.securitytracker.com/id/1029684
http://www.securityfocus.com/bid/65125
http://www.openwall.com/lists/oss-security/2014/01/24/6
http://support.citrix.com/article/CTX200288
http://security.gentoo.org/glsa/glsa-201407-03.xml
http://secunia.com/advisories/56650
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00011.html
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00010.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-February/127607.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-February/127580.html