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Web Application Firewall Use Case: Continuous Security Assessment

After some deliberation, I have decided to add Continuous security assessment as a standalone item on my web application firewall use cases list. Although some could argue the functionality is already covered in the Web intrusion detection and prevention section, it is not obvious—you have to understand this field in order to know it is there.

Continuous security assessment is not specific to web application firewalls—it's been used for the network layer for years—but web application firewalls are more useful for web applications (than IDS tools are for network applications), simply because there's essentially one data format to analyse (if you can call a bunch of loosely related specifications used by web applications "one" data format). With web applications, you get to see clear picture of application input and output. Therefore, with proper parsing and analysis in place, it's almost like having a direct communication channel with the application itself.

The focus here is not on the attacks and other suspicious client behaviour, which comes out of the stock IDS/IPS functionality, but on everything else:

  • application defects,
  • information leakage,
  • configuration errors,
  • change control

and so on. The advantage is that you can detect some very subtle issues, only possible because of the depth of analysis.

Just as an extreme example, there are quite a few web applications out there where SQL injection (less often) and XSS (surprisingly common) exist by design—their clients are allowed and expected to send such low-level stuff and have it executed by the server. These types of problem can be detected early and with little effort, and because assessment never stops, you get the alert as soon as they are manifested.

Note: This post is part of the Web Application Firewall Concepts series.

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