The hvm_msr_read_intercept function in arch/x86/hvm/hvm.c in Xen 4.1 through 4.4.x uses an improper MSR range for x2APIC emulation, which allows local HVM guests to cause a denial of service (host crash) or read data from the hypervisor or other guests via unspecified vectors.
http://lists.fedoraproject.org/pipermail/package-announce/2014-October/140199.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-October/140418.html
http://lists.fedoraproject.org/pipermail/package-announce/2014-October/140483.html
http://lists.opensuse.org/opensuse-security-announce/2014-10/msg00002.html
http://lists.opensuse.org/opensuse-security-announce/2014-10/msg00003.html
http://secunia.com/advisories/61664
http://secunia.com/advisories/61858
http://secunia.com/advisories/61890
http://security.gentoo.org/glsa/glsa-201412-42.xml
https://exchange.xforce.ibmcloud.com/vulnerabilities/96785
http://support.citrix.com/article/CTX200218
http://support.citrix.com/article/CTX201794
http://www.debian.org/security/2014/dsa-3041