Redefining the Perimeter

3:35 PM -- Every other month, I read an article or blog that talks about the network perimeter being dead. But it isn’t that the perimeter is dead; it’s just changed.

It used to be that enterprise networks had a well-defined perimeter, where a firewall separated internal hosts from the scary, hacker-laden Internet. Holes would be poked into the firewall to allow external hosts to access a few well-protected mail and Web servers, maybe DNS, but that was it.

Then came the mobile workforce, which required bigger holes in the firewall -- usually in the form of a VPN -- to allow the road warriors to get their work done while they were traveling around the world. Malicious hackers took advantage of those mobile devices and used them as jumping points into the corporate network.

Today, this is the kind of thing that keeps security pros awake at night. These remote endpoints have a level of access similar to the level they'd have on company property. Essentially, they become extensions of the perimeter.

Location-aware host-based firewalls have stepped into help make managing the firewalls on endpoints easier. The concept is simple: If the laptop is in the office, the firewall will be disabled or very relaxed; if it is anywhere else, it will tighten up like Fort Knox. Most of the major endpoint security vendors have adapted this technology in the last year and a half.

Location-aware firewalls work by analyzing network characteristics assigned through DHCP-like IP address, subnet, gateway, and DNS servers. If the network properties match pre-defined parameters, then a specific firewall is applied.

If you’re looking at this technology or already have it in place, I encourage you to not overlook the importance of the firewall rules for when the host is within the internal network. Don’t assume that since it is within your corporate perimeter that it is safe.

Imagine if a stolen laptop used disk encryption so the hard drive couldn’t be removed and analyzed -- yet booted up within Windows waiting for a user and password. A determined attacker could learn enough about your internal network that they could simulate it in order to trick the machine into opening itself up to attack.

Security technologies are great... until they can be used against you. Be diligent in all aspects of host-based protection, because each one is a backdoor into your network.

– John H. Sawyer is a security geek on the IT Security Team at the University of Florida. He enjoys taking long war walks on the beach and riding pwnies. When he's not fighting flaming, malware-infested machines or performing autopsies on blitzed boxes, he can usually be found hanging with his family, bouncing a baby on one knee and balancing a laptop on the other. Special to Dark Reading