Kind of sounds funny in today's Information Technology context, doesn't it? However, it should at least sound familiar to many of us in the IT security realm. We've been following these practices for years, after all.
The problem is that it's too late. We have no perimeter to secure, no matter how hard we try to convince ourselves that we do.
Perhaps you're not convinced. Perhaps you think I'm just spewing fear, uncertainty, and doubt (aka FUD) like so many do these days. Well, let me try to convince you:
Just as software developers came up with SOAP to get around our firewalls, they've come up with a whole class of software that opens and retains network connections to external systems. These include desktop instant messenger applications, many Voice over IP applications, etc. Notice how popular IM has become in the past few years? Notice how popular Skype and all the others are becoming?
Take a closer look at how Skype works behind a firewall sometime. On a typical home network router that prevents all unsolicited incoming network connections, Skype runs just fine, even allowing unsolicited incoming phone calls while the user remains connected to Skype.
The software has circumvented the firewall, folks. It opens and retains an active network connection out to the Skype infrastructure, which happens to be peer-to-peer (P2P). How much do you know about the IM/VoIP software running on all of your desktops? How much do you know about the external servers and P2P networks that are required to make these applications function?
Blocking those ports at the firewall, you say? Well, your users are pretty smart people. In all likelihood, they disable the VPN client software and run their own software on their laptops or desktops, and gleefully connect to these services.
I hope you're convinced by now that the perimeter, at the very least, is not as clear a line as you may have thought it was.
I say there is no perimeter per se; there is just a multitude of defensive products and features spread haphazardly throughout our networks. That's probably too far to the other extreme, but I think the concept is not all that far fetched.
I also want to emphatically note that I'm not saying AIM, Skype, and the like shouldn't be used. Quite the contrary. I love them both, and I'm an avid user of both. The benefits justify their use, to me. Well configured, they can be powerful business and personal tools.
My main point is that our notion of a security perimeter is at best antiquated. At worst, it's a dangerous way of thinking.
Until and unless we concentrate our security efforts on the software, all of the security perimeters we devise will be swept aside. We cannot afford to presume that our security perimeter products will protect us against bad software -- no matter how much we've paid for them.
The status quo today is that a security vulnerability in some basic applications can punch right through our 'perimeter' and send us IT security folks scrambling to put out yet another fire.
That doesn't instill me with much confidence, and I hope it doesn't for you either.
Kenneth van Wyk, a 19-year veteran of IT security, is the prinicpal consultant for KRvW Associates, LLC. The co-author of two security-related books, he has worked at CERT, as well as at the U.S. Department of Defense.