The HYPERVISOR_xen_version hypercall in Xen 3.2.x through 4.5.x does not properly initialize data structures, which allows local guest users to obtain sensitive information via unspecified vectors.
https://security.gentoo.org/glsa/201504-04
http://xenbits.xen.org/xsa/advisory-122.html
http://www1.huawei.com/en/security/psirt/security-bulletins/security-advisories/hw-423503.htm
http://www.securitytracker.com/id/1031837
http://www.securitytracker.com/id/1031806
http://www.securityfocus.com/bid/72955
http://www.debian.org/security/2015/dsa-3181
http://support.citrix.com/article/CTX200484
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00014.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-March/152776.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-March/152588.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-March/152483.html