At a very fundamental level, you can begin to protect and police access to your VPN by ensuring that the software is always up to date, ensuring that you’re on top of any patches needed as well as any zero-days that may have been released for that VPN. And, of course, ensuring you have password strength policies in place with specific recommendations for creating the most secure.
Protecting a VPN: beyond the basics
Once you are up to date and patched, there is much more to be done to keep VPN access secure and the network protected. Start by denying IP connections and authentications from any network, internet asset, or software that anonymizes connection. You want to ensure that you can trace and log connections to specific addresses.
Ensure that you include in your employee policies and guidance a list of connections that are allowed into your network — no user should use services such as TOR (The Onion Router) to gain access to your firm’s network. Set up account lockout policies as well as an appropriate password policy so that long and strong passwords are not only encouraged but mandatory.