Use-after-free vulnerability in QEMU in Xen 4.5.x and earlier does not completely unplug emulated block devices, which allows local HVM guest users to gain privileges by unplugging a block device twice.
www.securityfocus.com/bid/76152
www.securitytracker.com/id/1033175
xenbits.xen.org/xsa/advisory-139.html
lists.fedoraproject.org/pipermail/package-announce/2015-September/165373.html
lists.fedoraproject.org/pipermail/package-announce/2015-September/167792.html
lists.fedoraproject.org/pipermail/package-announce/2015-September/167820.html