The remote host is running a version of MacOS that is affected by a root authentication bypass vulnerability.
The remote host is running a version of MacOS 10.13 or 10.13.1 that is missing a security update. It is, therefore, affected by a root authentication bypass vulnerability. A local attacker or a remote attacker with credentials for a standard user account has the ability to blank out the root account password. This can allow an attacker to escalate privileges to root and execute commands and read files as a system administrator.
Install Security Update 2017-001 or later. Alternatively, enable the root account and set a strong root account password.