Versions mentioned in the description apply to the upstream
Remediation section below for
Ubuntu:18.04 relevant versions.
An exploitable denial-of-service vulnerability exists in Systemd 245. A specially crafted DHCP FORCERENEW packet can cause a server running the DHCP client to be vulnerable to a DHCP ACK spoofing attack. An attacker can forge a pair of FORCERENEW and DCHP ACK packets to reconfigure the server.
systemd to version 237-3ubuntu10.49 or higher.