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Next-generation intrusion prevention: The pre-attack period

Martin Roesch, lead developer of Snort IDS, explains the role of intrusion prevention prior to an attack.

At a macro-level, configuration management is perhaps the best term to describe the activities associated with this phase – although the case could also be made for calling it vulnerability management. Regardless, for our purposes the pre-attack period can logically be divided into two separate timeframes.

Assessments are typically made relatively long before an attack (i.e., days, weeks) to establish proper configuration of the computing environment. This entails identifying discrepancies from established policies as well as vulnerabilities, both those that are the result of coding deficiencies and those that are the result of configuration "errors." Various scanning technologies are applicable and findings are subsequently addressed, typically by implementing patches, re-configuring affected devices or re-configuring upstream security devices.

Clearly these are all positive, preventive measures. Yet they describe a conventional approach. It is based on periodic snapshots and is therefore diminishing in value as the time between vulnerability discovery and the appearance of an associated exploit consistently shrinks. In contrast, a defining characteristic for next-generation intrusion prevention is the ability to significantly reduce the period between assessments, ideally offering some degree of always-on, passive scanning capability in conjunction with on-demand, highly-targeted active scanning.

The second part of the pre-attack period occurs immediately prior to a potential attack. This is the domain of conventional access control tools such as firewalls and routers with ACLs that can stop an imminent attack as a matter of routine enforcement of the rules that comprise their configuration. By no means a sufficient defense against attacks, these tools are still very effective in terms of making the problem space more manageable. As will be discussed in part three, there is also the potential to use them more dynamically to assist with attack mitigation.

In the next installments we'll take a closer look at the technologies and processes associated with the attack and post-attack periods.


  A continuum of capabilities
  The pre-attack period
  Time zero (during the attack)
  The post-attack period
  The power of an integrated system

Martin Roesch founded Sourcefire in 2001 and serves as its Chief Technology Officer. A respected authority on intrusion detection technology and forensics, he is responsible for the technical direction and product development efforts. Martin, who has 17 years industry experience in network security and embedded systems engineering, is also the author and lead developer of the Snort Intrusion Detection System ( that forms the foundation for the Sourcefire 3D System.

This was last published in September 2005

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