steve288
If you have port forwarded in your router (in conjunction with enabling server manager access in the server manager Remote Access panel), you are using https, then theoretically anyone on the net can access it, it's just a matter of falsifying their source IP & hacking the password.
Edit - This statement is not correct as Charlie points out in a later post ie "because of the way TCP works, it's not possible to make a port-forwarded connection from the Internet through a router using a spoofed source IP address of 192.168.X.y. The TCP handshake will fail and there will be no connection. The risk you've identified just does not exist."
So you only have one level of security (password) to protect probably the most important "function" on your server.
Edit - and this statement only applies if a hacker is accessing via a site IP specified in the remote access panel.
Edit - This whole issue is why it is not recommended to allow access to server manager from anywhere on the Interent, using the appropriate setting (which I will not repeat here).
Under those conditions it is just a matter of hacking the admin password.
Using the VPN method requires a VPN to be established first which makes you a part of the local network, so security is better, but recently we see issues where VPN connections are less than secure as the ISP can read your communications if they choose to. There may be a shift away from the use of VPN because of this security issue.
By tunnelling you use a secure ssh connection, as good as it gets in a practical world, so security is reasonably well assured. After establshing the tunnel using Putty, typically you then open a browser at
https://localhost/server-managerssh using tunnelling or command line input is the most secure method.
Port forwarding is not really the connection method, it's just allowing the connection to be fowarded by your router to your sme server, where your router is acting as your local gateway, note you are using https then, and all that is needed to gain access to your system is a correct password. So make sure you use really strong passwords for server manager, and always specify the remote connection fixed IP (in server manager Remote Access panel).