Simple MAC framework policy to disable access to networking for
certain group.  Running kldload mac_nonet.ko to load the kernel
module.  The load action require root permissions.

Set gid that shouldn't access the network: 
    sysctl security.mac.nonet.gid=31337
and enable enforcing:
     sysctl security.mac.nonet.enabled=1
     
Any call to socket(2) from user in this group will end with EPERM.
You can also select group that can access only AF_UNIX sockets with
security.mac.nonet.local_gid.

WWW: https://github.com/pbiernacki/mac_nonet