CRS - OWASP ModSecurity Core Rule Set

The OWASP ModSecurity Core Rule Set (CRS) is a set of generic attack detection rules for use with ModSecurity or compatible web application firewalls. The CRS aims to protect web applications from a wide range of attacks, including the OWASP Top Ten, with a minimum of false alerts.

The Core Rule Set provides protection against many common attack categories, including:

SQL Injection (SQLi)
Cross Site Scripting (XSS)
Local File Inclusion (LFI)
Remote File Inclusion (RFI)
Remote Code Execution (RCE)
PHP Code Injection
HTTP Protocol Violations HTTPoxy
Shellshock
Session Fixation
Scanner Detection
Metadata/Error Leakages
Project Honey Pot Blacklist
GeoIP Country Blocking

New Features in CRS 3

CRS 3 includes many coverage improvements, plus the following new features:

Over 90% reduction of false alerts in a default install
A user-defined Paranoia Level to enable additional strict checks
Application-specific exclusions for WordPress Core and Drupal
Sampling mode runs the CRS on a user-defined percentage of traffic
SQLi/XSS parsing using libinjection embedded in ModSecurity

For a full list of changes in this release, see the CHANGES document.

Installation

CRS 3 requires an Apache/IIS/Nginx web server with ModSecurity 2.8.0 or higher.

Download CRS.

git clone https://github.com/SpiderLabs/owasp-modsecurity-crs.git

After download, copy crs-setup.conf.example to crs-setup.conf. Optionally edit this file to configure your CRS settings. Then include the files in your webserver configuration:

Include /.../crs-setup.conf
Include /.../rules/*.conf

For detailed installation instructions, see the INSTALL document. Also review the CHANGES and KNOWN_BUGS documents.
You can update the rule set using the included script util/upgrade.py.

Handling False Positives and Advanced Features

Advanced features are explained in the crs-setup.conf and the rule files themselves. The crs-setup.conf file is generally a very good entry point to explore the features of the CRS.
We are trying hard to reduce the number of false positives (false alerts) in the default installation. But sooner or later, you may encounter false positives nevertheless.

Christian Folini's tutorials on installing ModSecurity, configuring the CRS and handling false positives provide in-depth information on these topics.

Core Team