It's not really an issue, it's by design, a basic firewall policy will deny all inbound and permit all outbound. You can naturally try to control your outbound traffic, but be ready to respond to the flood of the phone rings heading your way. Access-list updates and blocked traffic log reviews is what you'll be looking at most of your day. You will find that many network apps and services are difficult to tie to a single port, or even port ranges.
It's better to just segment your network with VLANs and limit traffic to high security resources only.