An issue was discovered in Xen through 4.9.x allowing guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode.
www.openwall.com/lists/oss-security/2017/12/12/3
www.securityfocus.com/bid/102172
www.securitytracker.com/id/1040770
lists.debian.org/debian-lts-announce/2018/01/msg00003.html
lists.debian.org/debian-lts-announce/2018/10/msg00009.html
security.gentoo.org/glsa/201801-14
support.citrix.com/article/CTX232096
www.debian.org/security/2018/dsa-4112
xenbits.xen.org/xsa/advisory-250.html