If someone compromises the host system you are in trouble.
Not only the host. You have to trust every client to behave, as @forbiddenlake already mentioned, NFS relies on IDs that clients can easily fake to pretend they are someone else. Without rolling out all the Kerberos stuff, there really is no security when it comes to NFS.
For it to be bulletproof, it would help if it came with security built in. Kerberos is a complex mess.