Firewall Wish List

Or, why you should absolutely perform outbound firewall filtering



5:35 PM -- Firewalls aren't just for blocking people from sending traffic to your network. If you've been using them in that way alone, you are missing out on half their value. Firewalls have become ubiquitous, but they are also rarely used to their entire effectiveness.

You've got one, or 50, sitting in your data center, whirring away, doing whatever packet inspection magic they advertise on the box, but what do you really want in a firewall? You want something that stops malicious activity, you want it to protect your assets, you want it to scale, and you want it to be cost effective. Firewalls have been around for many years, yet they are still misused almost as often as they are used.

When people set up a Web server on their network, they typically open port 80 to the world, but they also open it in both directions. The reason for this is completely unexplained in most cases, since it's entirely unneeded, unless the application somehow needs to contact other Websites. That's generally only needed in the case of blog sites, or sites that use other Web services.

Even in the case of Web services it can be locked down so the only sites it can communicate to are those services. Additionally, patch management sites can also be whitelisted. That way the site retains all its functionality but is far more secure. And why? Web servers never need to connect to the Web, however, one of the most frequently used attacks is creating reverse shells over port 80. In other words, the attacker pulls in PHP-include payloads from other Web servers over port 80.

Unless there is a good reason to allow your Website to make outbound requests to other Websites, you can lock your site down quite a bit by performing egress (outbound) firewall filtering. If you aren't doing it, your network administrators aren't giving you your money's worth. If they haven't done this yet, you may want to revisit your network security architecture and lock down those sites.

— RSnake is a red-blooded lumberjack whose rants can also be found at Ha.ckers and F*the.net. Special to Dark Reading.

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