Xen, when used on a system providing PV backends, allows local guest OS administrators to cause a denial of service (host OS crash) or gain privileges by writing to memory shared between the frontend and backend, aka a double fetch vulnerability.
http://lists.opensuse.org/opensuse-security-announce/2016-03/msg00094.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00045.html
http://lists.opensuse.org/opensuse-security-announce/2016-07/msg00005.html
https://security.gentoo.org/glsa/201604-03
http://www.debian.org/security/2016/dsa-3434
http://www.debian.org/security/2016/dsa-3471
http://www.debian.org/security/2016/dsa-3519
http://www.oracle.com/technetwork/topics/security/ovmbulletinjul2016-3090546.html