The remote Debian host is missing a security-related update.
Several vulnerabilities have been discovered in the Linux kernel that may lead to a privilege escalation, denial of service or information leaks. - CVE-2018-15471 (XSA-270) Felix Wilhelm of Google Project Zero discovered a flaw in the hash handling of the xen-netback Linux kernel module. A malicious or buggy frontend may cause the (usually privileged) backend to make out of bounds memory accesses, potentially resulting in privilege escalation, denial of service, or information leaks. - CVE-2018-18021 It was discovered that the KVM subsystem on the arm64 platform does not properly handle the KVM_SET_ON_REG ioctl. An attacker who can create KVM based virtual machines can take advantage of this flaw for denial of service (hypervisor panic) or privilege escalation (arbitrarily redirect the hypervisor flow of control with full register control).
Upgrade the linux packages. For the stable distribution (stretch), these problems have been fixed in version 4.9.110-3+deb9u6.