The remote Debian host is missing a security-related update.
Multiple vulnerabilities have been discovered in the Xen hypervisor : - CVE-2018-12891 It was discovered that insufficient validation of PV MMU operations may result in denial of service. - CVE-2018-12892 It was discovered that libxl fails to honour the 'readonly' flag on HVM-emulated SCSI disks. - CVE-2018-12893 It was discovered that incorrect implementation of debug exception checks could result in denial of service.
Upgrade the xen packages. For the stable distribution (stretch), these problems have been fixed in version 4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9.