systemd fails an assertion in manager_invoke_notify_message when a zero-length message is received over /run/systemd/notify. This allows a local user to perform a denial-of-service attack against PID 1.Proof-of-concept:NOTIFY_SOCKET=/run/systemd/notify systemd-notify “”

Source: Assertion failure when PID 1 receives a zero-length message over notify socket · Issue #4234 · systemd/systemd · GitHub