The great intrusion prevention debate

Will the intrusion prevention system revolutionize security? Or is it just another point solution?

No security topic generates more spirited debate than intrusion prevention. Deployed on the edge -- and increasingly, deep inside -- the network, IPSes (intrusion prevention systems) purport to identify and stop attacks before they start based on constantly updated threat profiles. In this Point/Counterpoint, we’ve pitted Marc Willebeek-LeMair, CTO and Chief Strategy Officer of 3Com’s security division, TippingPoint, against Martin Roesch, CTO and founder of Sourcefire (and the inventor of Snort). TippingPoint’s Willebeek-LeMair is bullish on the supreme effectiveness of his IPS approach; Sourcefire’s Roesch positions IPSes, which his company also sells, as just one component of an integrated network defense system. The clash of these two partisans reveals much about the state of network protection and the rivalry between hardware and software security vendors.

Marc Willebeek-LeMair: To understand what an IPS is, you need to grasp the problem it aims to solve. Today’s cyberthreat environment is increasingly severe, compounded by the growing number of vulnerabilities that are discovered weekly, the emergence of new types of attacks (such as blended threats and spyware), the shrinking time between vulnerability discovery and exploit development, the propagation speeds of automated worm attacks, and the dissolving network perimeter.

IT security teams are overwhelmed, and traditional point solutions such as firewalls, anti-virus software, and IDSes are inadequate protection by themselves. The threat landscape is further exacerbated by the challenges involved in applying patches in a timely manner, and also by organizations that cannot enforce patch management -- universities, ISPs, and so on. What’s needed is a new type of security element that pervades the network and automatically protects organizations from a broad variety of attack types and from all potential points of attack -- inside or out.

Martin Roesch: Marc, you’ve done a great job of defining the threat environment. But the in-line network IPS as it’s implemented and deployed today provides only the most basic capability to actually address the problem. In-line IPS is positional and can only block based on threats it has a prior knowledge of or basic thresholds in flood-style DoS/worm traffic. Inline IPS requires the attacks and attackers to transit predefined choke points on the network in order for it to perform its task. Clearly, if we are to address the pervasive threat environment, then we need a pervasive system that allows us to not just block things we know about crossing discrete points on the network, but one that can also enforce network security policy by managing and reducing exposure to attacks in the first place. Blended threats require blended security systems that have more remediative options. In-line intrusion prevention is a step in the right direction, but I believe that the infrastructure itself can be orchestrated effectively to provide a much broader capability than just point defense in the face of a pervasive threat.

MWL: While I agree with your assertion that the infrastructure can be orchestrated to provide more comprehensive protection, I do not agree that IPS is simply a point defense. Unlike a firewall, IPS is not being deployed just at the perimeter, but throughout the entire network to protect the core as well as internal segments. To meet the stringent networking requirements (latency, throughput, reliability) that these core and internal network locations demand, state-of-the-art IPSes are based on purpose-built custom hardware like other network infrastructure devices such as switches and routers.

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.

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.

Practically speaking, this is a pretty thin layer of protection, because it has to handle client- and server-side attacks, random file formats and e-mail attachments, encryption, segmentation, custom applications, and arbitrary protocols that your hardware-based protocol analyzers cannot know how to interpret beyond a simple regular-expression-analysis capability. True proactive security means you must block identifiable threats as well as enforce security policy so as to reduce exposure in the first place -- in addition to detecting change that indicates compromise independent of threat detection. A proactive security solution should also be able to defeat a threat emerging from any point on the network, not just pre-identified ingress/egress points. Most IPS companies ignore these points, leading end-users to believe that traditional, stand-alone IPS technology is capable of proactively protecting assets throughout the network, even though they have no context about the systems they are trying to protect. This positioning is not only false; it’s unfair to the end-user.

MWL: To be as polite and as succinct as possible: You are simply misinformed. I would strongly recommend you take a closer look at the state-of-the-art IPS. You’d be surprised to find several significant differences from your perception and reality.

Very accurate filters can be written based on vulnerability information, not exploit information. That is the definition of proactive protection: customers are protected before the attack (exploit) exists in time and space. These filters precede the existence of an exploit and proactively protect against any exploit targeting that vulnerability. You are, however, correct that writing good filters takes extensive research, requires very sophisticated skills and testing, and is an enormous differentiator between the various IPS solutions that exist today.

It’s typical for software-solution vendors to misrepresent a hardware solution as fixed and inflexible. Again, this is misinformation or, in the best case, laziness. Reality is that any hardware design -- for example, a CPU -- consists of hardware building blocks like the arithmetic control unit, the floating point unit, or another component that specializes in accelerating a particular operation. Specialization does not stop it from being programmable or flexible. A common, simplistic, and naïve perspective of IPS implementation would assume that each protocol is hard-coded into the hardware. State-of-the-art systems don’t do that at all. They boil down the problem into building blocks that are much more general and serve to accelerate processing for the specific task at hand.

Beyond vulnerability filters, IPSes use network profiling to characterize a particular network environment to determine what is “normal” behavior in that environment. Deviations from what is normal (without any knowledge of an exploit or vulnerability) can be alerted on, blocked, or throttled. Protection based on deep understanding of baselines and changes in network behavior is proactive by any definition.

Intrusion prevention has reached the point where the technology has been tested extensively and is now broadly deployed by hundreds of Fortune 500 customers worldwide. Talk to them. Start at the very top of the list.

When we pioneered IPS in 2002, IDS vendors unanimously claimed it was impossible. Most were quick to point out that false positives and latency would adversely impact the network. Ironically, these problems were created by inferior implementations of IDS products. Today every single IDS vendor offers an IPS. The problem is, not all IPSes are created equal, and indeed most of the shortcomings you highlight are true for the vast majority of these products, but not all. Second, it is common practice for naysayers to pick a corner case scenario that cannot be caught by today’s IPS products and to ignore the other 99 percent of cases that are fully covered.

MR: Misinformed? Please. Sourcefire, with the broader Snort community, invented the techniques for identifying threats targeting an underlying vulnerability -- as opposed to simple exploit signatures. Regarding the hardware-vs.-software debate, knowing the performance of our IPS products on today’s advanced network platforms -- near-zero latency at up to 8 gigabits -- while also knowing that we can adapt infinitely more quickly and cost-effectively than hardware-based approaches certainly allows me to sleep much better at night.

When Sourcefire questioned those who declared IDS dead, it wasn’t because we saw no value in the blocking function. It was because we knew that the blocking function could never be 100-percent effective. Your acknowledgement of the need for behavioral anomaly detection argues that exact point. Leveraging persistent awareness of network assets -- their composition, behaviors, vulnerabilities, and change -- is at least as important as inspecting the traffic targeting those assets. So rather than simply following the herd, Sourcefire has both embraced IPS -- one of our products won Best Intrusion Solution at this year’s RSA show -- while also recognizing the limitations of any filtering technology in the broader landscape of network threat.

When the final chapter on this debate is written, I am confident that intrusion prevention will mean much more than just IPS.

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