Guest Permissions on User Databases
Applies To: SQL Server 2016
This rule determines whether the guest user has permission to access the database. This rule applies to user databases only.
Revoke the guest user permission to access the database if it is not required.
The guest user cannot be dropped, but guest user can be disabled by revoking its CONNECT permission by executing REVOKE CONNECT FROM GUEST within any database other than master, tempdb, or msdb.