Securely allow SSH from Parallels to Host MacOS w/o risking Network threats?
You can edit /etc/ssh/sshd_config and set the parameter "ListenAddresss" to only the IP-address your host Mac has on the dedicated VNet you have create between the host and the virtual machine (host-only networking).

Remember to remove:

  ListenAddress 0.0.0.0
  ListenAddress ::


and replace it with just:

  ListenAddress 176.16.236.111


(where 176.16.236.111 should be replaced with whatever your IP-address is on that private network)