Cybersecurity

We are trying to implement a NAS solution with UNIX servers and multiple networks, and I've heard that NFS has security issues with lockd and statd.

The security issue as it was explained to me is that these services are subject to vulnerabilities/exploits, and that users who connect to Unix servers through a VPN can exploit the lockd/statd services, and then compromise another user, i.e., go out another VPN to another network.

Can someone explain this further?

You must insure that the versions of network daemons such as the services you decribe in your post are running the lastest patches which have addressed the vulnerabilites you are concerned about. Most software with known vulnerabilites has patches to close the security holes. NFS has had many vulnerablities, historically, over the years; but they are patched and newer versions fixed. You should check to see what versions you are running and make sure you have the latest versions.