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Monday, June 30, 2014

(T) How to use the Windows Firewall behind a NAT router

Ever wanted to open up a port on your home firewall, but restrict it more than a NAT router allows with raw port 1234 to IP

Restrict it by an actual application, or 1 or 2 remote addresses, not to the whole system from anywhere on the Internet? Or easily change it because of DHCP changes on either local or remote systems? Or to allow a cloud service to send data back to one of your systems? Or allow a Web a console you want to remote into from work to check your Security System?

While playing with Splunk I found the logic of the Windows Firewall behind a NAT router changes things a bit.

The Windows Firewall has 3 Zones, you usually see this PopUp from your browser when you join a new Wireless network on your laptop for example. You will see 'Public' and 'Private' or 'Home' which is also 'Private', there is also 'Domain' for AD attached systems which we generally don't have at home.

When you are behind a NAT router you can ignore or disable everything but 'Private'. Once you open port 1234 to IP on your home router via Port Forwarding, Gaming or whatever your router calls it, all traffic to the a Windows Firewall is seen as 'Private' or inside your network. You can test this by disabling a 'Public' rule you have for a Remote Access for example and it will still work, because it uses the 'Private' rule once NAT is involved.

So everything you will do will be an Inbound Rules and 'Private'. Notice in the image above I have VNC Server installed on my test system and it has 'Public Disabled'. Even though I remote to it over the Internet from a public address, once NAT port forwarding takes over it becomes a 'Private' rule.

Also notice that I have a Splunk Web rule that is also 'Private'. All I have to do now is craft my NAT router to pass any port range I want to the IP I want and then use the Windows Firewall to further restrict it by the remote IP's allowed to the computer or specific application. This allows me to refine my port hole in my NAT router to only the systems I want to remote from and to only the actual application (VNC Server.exe) on that port.

If your home IP changes due to DHCP renewals, then use a Dynamic DNS provider so you can refer to it by name instead of IP. This will require you to run a small utility on your system to send any IP changes to your Dynamic DNS provider.

Play with it and let me know any other tricks you might use.

#InfoSec #HackerHurricane