Use-after-free vulnerability in the FIFO event channel code in Xen 4.4.x allows local guest OS administrators to cause a denial of service (host crash) and possibly execute arbitrary code or obtain sensitive information via an invalid guest frame number.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2016-8022
http://xenbits.xen.org/xsa/xsa188.patch
http://xenbits.xen.org/xsa/advisory-188.html
http://www.oracle.com/technetwork/topics/security/ovmbulletinjul2016-3090546.html
http://www.debian.org/security/2016/dsa-3663
http://www.c7zero.info/stuff/csw2017_ExploringYourSystemDeeper_updated.pdf