A flaw was found in the way qemu v1.3.0 and later (virtio-rng) validates addresses when guest accesses the config space of a virtio device. If the virtio device has zero/small sized config space, such as virtio-rng, a privileged guest user could use this flaw to access the matching host's qemu address space and thus increase their privileges on the host.
https://security-tracker.debian.org/tracker/CVE-2013-2016
https://github.com/qemu/qemu/commit/5f5a1318653c08e435cfa52f60b6a712815b659d
https://exchange.xforce.ibmcloud.com/vulnerabilities/83850
https://access.redhat.com/security/cve/cve-2013-2016
http://www.securityfocus.com/bid/59541
http://lists.opensuse.org/opensuse-security-announce/2014-05/msg00002.html