The remote Debian host is missing a security-related update.
The Qualys Research Labs discovered multiple vulnerabilities in systemd-journald. Two memory corruption flaws, via attacker-controlled allocations using the alloca function (CVE-2018-16864, CVE-2018-16865 ) and an out-of-bounds read flaw leading to an information leak (CVE-2018-16866 ), could allow an attacker to cause a denial of service or the execution of arbitrary code. Further details in the Qualys Security Advisory at https://www.qualys.com/2019/01/09/system-down/system-down.txt
Upgrade the systemd packages. For the stable distribution (stretch), these problems have been fixed in version 232-25+deb9u7.