Anyone who knows just the host name and the listener name can have full control over the listener. They can stop the listener and also obtain detailed information about the listener, database, and…

'Lock the listener' is not a valid Oracle Net listener security feature or lsnrctl command.

'Hide the listener' is not a recognized Oracle listener security mechanism and does not prevent access by someone who already knows the listener name.

Creating multiple listeners multiplies the attack surface and does nothing to prevent unauthorized administrative access to any individual listener.

Running the listener on a remote client changes its location but does not add authentication, so the same unauthenticated access problem persists.

Oracle Net listener supports password-based authentication via the PASSWORDS_<listener_name> parameter in listener.ora or by using the 'change_password' command in lsnrctl. Once set, any lsnrctl administrative command (STOP, STATUS, RELOAD) requires the correct password, preventing unauthorized users who only know the hostname and listener name from controlling or interrogating the listener.

Storing listener.ora in a non-default directory relies on security through obscurity and does not require authentication to control the listener process itself.