Quick Emulator (Qemu) built with the VirtFS, host directory sharing via Plan 9 File System(9pfs) support, is vulnerable to an improper access control issue. It could occur while accessing virtfs metadata files in mapped-file security mode. A guest user could use this flaw to escalate their privileges inside guest.
https://security.gentoo.org/glsa/201706-03
https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg03663.html
https://lists.debian.org/debian-lts-announce/2018/09/msg00007.html
https://bugzilla.redhat.com/show_bug.cgi?id=1451709