You should be safe if you disallow multicast traffic from your network to the internet (but that's almost natural behavior of multicast traffic, given the low TTL values), and vica versa. While on it, disallow traffic from private address space (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) from anywhere but your own network. You could also disallow 127.0.0.0/8 from anywhere but the local loopback interface.