The “Mobius Defense” is a somewhat novel defense model proposed by Pete Herzog, founder of ISECOM and lead author of the Open Source Security Testing Methodology Manual (OSSTMM). Before continuing to read the following post I suggest you take a few minutes and breeze through the slide deck linked here. It’s an easy and interesting read so get to it… Mr. Herzog suggests in this presentation that the “Defense in Depth” strategy, with regards to network defense, is ineffective and antiquated, and needs to be replaced with a new and updated defense model. His proposed model is called the “Mobius Defense”. The basic tenet of this defense is one in which each individual asset should be protected as if it were the only asset in the model as opposed to forming lines of defense to secure the entire asset base as a whole. Two important facets are stated in his presentation:

  • Network security is a zero sum game in which a single compromise is all that is required to “win”
  • The network perimeter is truly nonexistent

If we take the above two statements to be true, then there really are no clearly defined lines of defense in which we can accurately create a defense in depth model and instead we should secure the individual asset by limiting its in and out dataflow, minimizing trust, and implementing a minimal interconnectedness policy across the board. Distilled, the Mobius model creates a network security design that disregards network boundaries and theoretical demarcation lines in favor of “guerilla defense” in which every actor fends for themselves. So what does this mean for the application security landscape? If what Mr. Herzog presents is reality, then the application layer truly is the last, and best, line of defense (pardon the pun). With the degradation of the network perimeter, thanks in part to the iPhone, Blackberry, Web Browser, and other assorted peripherals and client based designs; there is a new found urgency to secure each individual network touch point to the best extent possible. It’s with this urgency in mind that application security assessments should move upward in the prioritization of security spending. While I don’t suggest that defense in depth should go away and die, I do suggest that we should focus on securing the most common target of attack, the application layer. If the paradigm of the network has changed shouldn’t our defense models change as well?

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Tyler Shields is a Senior Researcher for the Veracode Research Lab whose responsibilities include understanding and examining interesting and relevant security and attack methods for integration into the Veracode product offerings. He also keeps track of new developments from other computer science and information security researchers to ensure that Veracode technologies are always kept in line with the most recent security advancements.

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