The great intrusion prevention debate

These systems offer powerful filtering capabilities that can do much more than simply blocking “predefined network patterns” as a reaction to known exploits. Leading-edge IPSes support a filtering language that can express complex conditions to detect both known and unknown exploits. These filters go beyond legacy string-matching signatures and are sometimes referred to as anomaly filters or vulnerability filters. They are designed to protect against any attack -- known or unknown -- that is crafted to exploit a particular vulnerability. A key component to an IPS system is the filter-update service that comes with it. The service, measured by the timeliness, accuracy, and comprehensiveness of new filters, provides automated protection against threats as they emerge. This proactive security is unique to IPS and is a game-changing tool.

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Today’s IPS systems are deployed as an overlay architecture onto existing networks. Soon, however, IPSes will be integrated within switch and router elements to provide the embedded infrastructure security you speak of. In effect, networking and security are converging. The new network node will offer the same packet-routing/switching functions of today’s networks but add a layer of intelligence that decides not only where a packet must go, but whether it should go at all. Networks will become much more dynamic than they are today by continuously adapting to filter out unwanted traffic based on old and new threats.

MR: All marketing claims notwithstanding, IPS technology is not proactive. A “filtering language” exists to predefine the conditions under which something is considered to be suspicious or malicious, therefore it is deterministic and based on foreknowledge of either how the protocol “should” work or based on knowledge of existing exploits against that protocol. What “leading-edge IPS filter languages” do is not substantively different than what we’ve been doing with the open source Snort engine (which can operate in IDS or IPS mode) for years now; we are also capable of detecting unknown exploits via both our rules language and protocol analyzers.

I’ll leave it for the reader to figure out if it’s a good idea to tear down network sessions automatically because a protocol decoder decided that a field size was larger than a guy in a lab thought it “should” be based on his limited understanding of the protocol and his limited exposure to the various clients and servers that implement it. Because in-line network IPSes have one analysis/response method and one practical position of deployment in order to bring their primary enforcement capability to bear, they are by definition point solutions no matter how deeply into the network you deploy them, just as firewalls are point solutions even though they are typically deployed deeply into today’s networks.

True proactive security would be able to do more than just identify the conditions under which an attack is occurring -- it would be a pervasive layer of intelligence overlaid on the network that could understand the network composition and enforce policy by properly orchestrating the capabilities of multiple disparate technologies as well as its own native detection and blocking capability. Relying solely on the timely updating of a signature service in order to have coverage presupposes that all possible attack vectors can be intercepted and all variations of an attack can be defined and detected before a compromise results. Not to mention that the signature collection would have to be comprehensive enough to cover every device, platform and application in your network.