sf.bin should not try to connect, AFAIK. But, it is updated "frequently" by Avast. The update should come from the avast.setup process, which is the one connecting and performing the engine and database updates.
Avast will keep trying to update sf.bin. You should delete all the firewall rules related to Avast (avastsvc.exe, avastui.exe, avast.setup...). Then set your firewall in "learning mode", reboot and then let the firewall to rebuild the rules related to Avast.
If any of the processes / services of Avast are not automatically allowed by the firewall, then add them manually, and reboot once again.
Please report back.