An issue was discovered in Xen through 4.10.x allowing x86 HVM guest OS users (in certain configurations) to read arbitrary dom0 files via QMP live insertion of a CDROM, in conjunction with specifying the target file as the backing file of a snapshot.
https://xenbits.xen.org/xsa/advisory-258.html
https://www.debian.org/security/2018/dsa-4201
https://security.gentoo.org/glsa/201810-06
https://lists.debian.org/debian-lts-announce/2018/10/msg00021.html