ModSecurity version 2.0 was first released in October 2006 and is a big improvement over the previous major version line. It is a substantial rewrite that changes the rule language and adds a lot of improvements such as:
Additional processing phases to give more fine-grained control over in which phase of the HTTP transaction a rule should be invoked
Regular expression back-references which allow you to capture parts of a regular expression and reference it later
Support for creating rules for XML data and much more
At the time this book was published, the latest major ModSecurity version was 2.5, and this version line adds even more enhancements such as the ability to reference a geographical database, which allows you to create rules that take action based on the geographical location of the user. Another interesting new feature is credit card number detection, which can be used to detect and prevent credit card numbers from being exposed through your web server. Of course, all the other security features that make ModSecurity such a great web application firewall have been refined and are available in the latest version, and we will learn all about them in the coming chapters.
Since version 2 of ModSecurity is such a different beast to previous versions, this book focuses only on this latest major version branch. This means that you must run Apache 2.0 or later, as ModSecurity 2 requires this Apache branch to function.
As Apache 1.x is a legacy branch that is now only infrequently updated (and when updated, mostly to patch known security vulnerabilities), now might be a good time to upgrade to the 2.x branch of Apache if you're still running an older version.
