Difference between revisions of "Category:OWASP ModSecurity Core Rule Set Project"

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* Franziska Bühler
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* Victor Hora
* Victor Hora
* Federico Schwindt
* Felipe Zipitría
* Manuel Spartan
== Presentation ==
== Presentation ==

Revision as of 14:48, 18 November 2017

Flagship big.jpg

OWASP ModSecurity Core Rule Set (CRS)

The 1st Line of Defense Against Web Application Attacks

The OWASP ModSecurity CRS Project's goal is to provide an easily "pluggable" set of generic attack detection rules that provide a base level of protection for any web application. 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.

More information at https://modsecurity.org/crs.


The OWASP ModSecurity CRS provides protections in the following attack/threat categories:
  • 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
  • Shellshock
  • Session Fixation
  • Scanner Detection
  • Metadata/Error Leakages
  • Project Honey Pot Blacklist
  • GeoIP Country Blocking

More Information at https://modsecurity.org/crs.


Getting Started / Tutorials

The following tutorials will get you started with ModSecurity and the CRS v3.

These tutorials are part of a big series of Apache / ModSecurity guides published by netnea. They are written by Christian Folini.

More Information about the rule set at https://modsecurity.org/crs and a full list of all the rules in the Core Rule Set at https://netnea.com/crs.


OWASP ModSecurity CRS is free to use. It is licensed under the Apache Software License version 2 (ASLv2), so you can copy, distribute and transmit the work, and you can adapt it, and use it commercially, but all provided that you attribute the work and if you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one.

Project Members

Project Leaders:


  • Christoph Hansen
  • Felipe 'Zimmerle' Costa
  • Franziska Bühler
  • Victor Hora
  • Federico Schwindt
  • Felipe Zipitría
  • Manuel Spartan


Related Projects

Quick Download

Source Code Repo

News and Events

Mailing List


Owasp-flagship-trans-85.png Owasp-defenders-small.png
License: ASLv2
Project Type Files CODE.jpg

<paypal>ModSecurity Core Rule Set Project</paypal>

The following tutorials will get you started with ModSecurity and the CRS v3.

These tutorials are part of a big series of Apache / ModSecurity guides published by netnea. They are written by Christian Folini.

More Information at https://modsecurity.org/crs.

ModSecurity Rules Language

What are the OWASP ModSecurity Core Rules (CRS) and why should I use them?

Using ModSecurity requires rules. In order to enable users to take full advantage of ModSecurity immediately, Trustwave's SpiderLabs is sponsoring the OWASP ModSecrity Core Rule Set (CRS) Project. Unlike intrusion detection and prevention systems which rely on signature specific to known vulnerabilities, the Core Rule Set provides generic protection from unknown vulnerabilities often found in web application that are in most cases custom coded. You may also consider writing custom rules for providing a positive security envelope to your application or critical parts of it. The Core Rule Set is heavily commented to allow it to be used as a step-by-step deployment guide for ModSecurity.

What attacks do the Core Rules protect against?

In order to provide generic web applications protection, the Core Rules use the following techniques:

  • HTTP protection - detecting violations of the HTTP protocol and a locally defined usage policy.
  • Common Web Attacks Protection - detecting common web application security attack.
  • Automation detection - Detecting bots, crawlers, scanners and other surface malicious activity.
  • Trojan Protection - Detecting access to Trojans horses.
  • Errors Hiding – Disguising error messages sent by the server

In addition the ruleset also hints at the power of ModSecurity beyond providing security by reporting access from the major search engines to your site.

How do I whitelist an IP address so it can pass through ModSecurity?

The first issue to realize is that in ModSecurity 2.0, the allow action is only applied to the current phase. This means that if a rule matches in a subsequent phase it may still take a disruptive action. The recommended rule configuration to allow a remote IP address to bypass ModSecurity rules is to do the following (where should be substituted with the desired IP address): background-color: #ffffcc; SecRule REMOTE_ADDR "@ipMatch 192.168.110" id:1,phase:1,nolog,pass,ctl:ruleEngine=Off

If you want to allow uninterrupted access to the remote IP address, however you still want to log rule alerts, then you can use this rule -

SecRule REMOTE_ADDR "@ipMatch 192.168.110" phase:1,nolog,allow,ctl:ruleEngine=DetectionOnly

If you want to disable both the rule and audit engines, then you can optionally add another ctl action:

SecRule REMOTE_ADDR "@ipMatch 192.168.110" phase:1,nolog,allow,ctl:ruleEngine=Off,ctl:auditEngine=Off

How do I handle False Positives and creating Custom Rules?

It is inevitable; you will run into some False Positive hits when using web application firewalls. This is not something that is unique to ModSecurity. All web application firewalls will generate false positives from time to time. The following Blog post information will help to guide you through the process of identifying, fixing, implementing and testing new custom rules to address false positives. http://blog.spiderlabs.com/2011/08/modsecurity-advanced-topic-of-the-week-exception-handling.html

Will using a large amount of negative filtering rules impact performance?

Yes. Each and every rule that you implement will consume resources (RAM, CPU, etc...). The two most important factors to consider with creating ModSecurity rules are the total number of rules and the Regular Expression optimizations. A single rule with a complex regular expression is significantly faster than multiple rules with simple regular expressions. Unfortunately, it is quite easy to create inefficient RegEx patterns. Optimizing RegExs by utilizing Grouping Only/Non-Capturing Parentheses can cut the validation time by up to 50%. The Core Ruleset is optimized for performance. background-color: #ffffcc;

What is a Virtual Patch and why should I care?

Fixing identified vulnerabilities in web applications always requires time. Organizations often do not have access to a commercial application's source code and are at the vendor's mercy while waiting for a patch. Even if they have access to the code, implementing a patch in development takes time. This leaves a window of opportunity for the attacker to exploit. External patching (also called "just-in-time patching" and "virtual patching") is one of the biggest advantages of web application firewalls as they can fix this problem externally. A fix for a specific vulnerability is usually very easy to design and in most cases it can be done in less than 15 minutes.


Managing Alerts

How do I manage ModSecurity logs if I have multiple installations?

If you have more then 1 ModSecurity installation, you have undoubtedly run into issues with consolidating, analyzing and responding to alert messages. Unfortunately, the original "Serial" format of the audit log was multi-line with all records held within one file. This made remote logging difficult. What was really needed was to have a mechanism to send logs onto a centralized logging host made specifically for processing ModSecurity Alert data. This is the purpose of the mlogc program. It comes with the ModSecurity source code and can be used to send individual audit log entries to a remote host in near real-time.

Is there an open source Console to send my audit logs to?

Christian Bockermann has developed an outstanding free tool called AuditConsole that allows you to centralize and analyze remote ModSecurity audit log data.

Can I send ModSecurity alert log data through Syslog?

Yes. If you already have a central Syslog infrastructure setup and/or if you are using some sort of SIEM application, then you might want to include the short version ModSecurity alert messages that appear in the Apache error_log file. You can easily reconfigure Apache to send its error logs through Syslog onto a remote, central logging server. However, the data being forwarded is a very small subset of the entire transaction. It is only a warning message and not enough information to conduct proper incident response to determine if there was a false positive or if it was a legitimate attack. In order to determine this information, you need access to the ModSecurity Audit log files.

Project Leader

Chaim Sanders

Project Contributors

See changelog for more contributors.

Project Users

OWASP/WASC Distributed Web Honeypot Project uses the Core Rule Set - https://www.owasp.org/index.php/OWASP_WASC_Distributed_Web_Honeypots_Project

cPanel distributes the OWASP CRS with their ModSecurity package - https://documentation.cpanel.net/display/CKB/OWASP+ModSecurity+CRS

Akamai's WAF Service is based on a previous version of the Core Rule Set - http://www.akamai.com/html/about/press/releases/2009/press_121409.html

CloudFlare's WAF uses the logic from the OWASP ModSecurity CRS - https://www.cloudflare.com/waf http://blog.cloudflare.com/cloudflares-new-waf-compiling-to-lua/

Verizon/EdgeCast WAF uses ModSecurity and the OWASP ModSecurity CRS - http://www.edgecast.com/services/security/#waf

Varnish Web Cache/Accelerator uses a converted version of the CRS - https://github.com/comotion/security.vcl

Project Sponsors

SpiderLabs Logo 2011.JPG

The CRS project is a small community within the bigger OWASP community. We have a successful project with a wide user base and with the CRS3 release cycle, we have put the development on new feet.

We have big plans and there is a need for all sort of contributions from people on a beginner and from people on an expert level alike.

Code : https://github.com/SpiderLabs/owasp-modsecurity-crs
Issues : https://github.com/SpiderLabs/owasp-modsecurity-crs/issues
Feature Requests : https://github.com/SpiderLabs/owasp-modsecurity-crs/issues (interleaved the issues, look for the right tag, currently candidate issue)

Summary of GitHub Shortcuts / Bookmarks

Plans for AppSecEU 2017

See separate page: Plans for AppSecEU 2017

Archive: v3.0 Detection Concepts / Goals

This page outlines development projects which would add new functionality to ModSecurity that could be leveraged by the OWASP ModSecurity Core Rule Set.

These are not listed in any particular order.

  1. Add New Detection Logic
    1. Fraud Detection (Session Hijacking/CSRF/Banking Trojans)
    2. User Profiling (GeoIP/Browser Fingerprinting)
    3. HoneyTraps
  2. Increase Rule Accuracy
    1. Reduce False Positives - many users complain about the number of false positives and the negative impacts (breaking functionality) when in blocking mode
    2. Reduce False Negatives - we need to constantly improve detection so that we don't miss attacks (http://blog.spiderlabs.com/2011/07/modsecurity-sql-injection-challenge-lessons-learned.html)
  3. Increase Performance/Reduce Latency
    1. Utilize set-based pattern matching (@pm/@pmf) for pre-qualification of regular expression checks
    2. Optimize individual @rx SecRules into less optimized versions
    3. Review all regular expression rules for performance (non-capturing/greediness).
  4. Improve Rule Management
    1. Make it easier for user to enable/disable the desired rules for their platform
    2. Update rule formatting for easier readability
    3. Reorder/Regroup rule into new file names

Archive: Detection Logic/Flow Concepts in the Request Header Phase

This section outlines the processing flow and associated points of detection and actions taken.

  1. IP Reputation
    1. Data inspected: REMOTE_ADDR
    2. Use @rbl to check against remote RBLs
    3. Use @pmf to check a local file if bad IPs
    4. Use GeoIP Data to assign fraud scores
    5. Actions
      1. Deny
      2. Increase TX anomaly score
      3. Tag client as "suspicious" in IP collection
  2. Request Method Analysis
    1. Data inspected: REQUEST_METHOD
    2. Compare the REQUEST_METHOD specified against:
      1. Allowed global methods set by the admin in the modsecurity_crs_10_setup.conf file
      2. Request methods allowed per-resource (GET vs. POST)
    3. Actions
      1. Deny
      2. Increase TX anomaly score
      3. Tag client as "suspicious" in IP collection
  3. Request Header Analysis
    1. Data inspected: REQUESTE_HEADERS
    2. Check for existence of malicious headers (User-Agent of scanners, etc..)
    3. Check for the absence of required headers (Host, User-Agent, Accept)
    4. Request Header Ordering Anomalies detects non-browsers/bots
    5. Actions
      1. Deny
      2. Increase TX anomaly score
      3. Tag client as "suspicious" in IP collection

Involvement in the development and promotion of OWASP ModSecurity CRS is actively encouraged! You do not have to be a security expert in order to contribute. Some of the ways you can help:

  • Contribute on the mail-list by answering questions from the community
  • Report issues to our GitHub Issue tracker

The upcoming major Core Rules (CRS) release 3.0.0 is currently being developed in a separate branch on github. The release is planned for the first quarter 2016. It brings incorporation of the @detectsqli and @detectxss operators and a general reduction of false positives for default setups.

Infos about 3.0.0


What does this OWASP project offer you?
What releases are available for this project?
what is this project?
Name: OWASP ModSecurity Core Rule Set Project (home page)
Purpose: ModSecurity is an Apache web server module that provides a web application firewall engine. The ModSecurity Rules Language engine is extrememly flexible and robust and has been referred to as the "Swiss Army Knife of web application firewalls." While this is certainly true, it doesn't do much implicitly on its own and requires rules to tell it what to do. In order to enable users to take full advantage of ModSecurity out of the box, we have developed the Core Rule Set (CRS) which provides critical protections against attacks across most every web architecture.

Unlike intrusion detection and prevention systems, which rely on signatures specific to known vulnerabilities, the CRS is based on generic rules which focus on attack payload identification in order to provide protection from zero day and unknown vulnerabilities often found in web applications, which are in most cases custom coded.

License: Apache Software License v2 (ASLv2)
who is working on this project?
Project Leader(s):
how can you learn more?
Project Pamphlet: Not Yet Created
Project Presentation: View
Mailing list: Mailing List Archives
Project Roadmap: View
Main links:
Key Contacts
current release
ModSecurity 2.2.8 - 06/30/2013 - (download)
Release description: == Version 2.2.8 - 06/30/2013 ==

Security Fixes:


  • Updatd the /util directory structure
  • Added scripts to check Rule ID duplicates
  • Added script to remove v2.7 actions so older ModSecurity rules will work
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/pull/43
  • Added new PHP rule (958977) to detect PHP exploits (Plesk 0-day from king cope)
 - http://seclists.org/fulldisclosure/2013/Jun/21
 - http://blog.spiderlabs.com/2013/06/honeypot-alert-active-exploits-attempts-for-plesk-vulnerability-.html

Bug Fixes:

  • fix 950901 - word boundary added
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/pull/48
  • fix regex error
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/pull/44
  • Updated the Regex in 981244 to include word boundaries
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/issues/36
  • Problem with Regression Test (Invalid use of backslash) - Rule 960911 - Test2
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/issues/34
  • ModSecurity: No action id present within the rule - ignore_static.conf
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/issues/17
  • "Bad robots" rule blocks all Java applets on Windows XP machines
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/issues/16
  • duplicated rules id 981173
 - https://github.com/SpiderLabs/owasp-modsecurity-crs/issues/18
Rating: Projects/OWASP ModSecurity Core Rule Set Project/GPC/Assessment/ModSecurity 2.2.8
last reviewed release
ModSecurity 2.0.6 - 2010-02-26 - (download)
Release description: ModSecurity is a web application firewall that can work either embedded or as a reverse proxy. It provides protection from a range of attacks against web applications and allows for HTTP traffic monitoring, logging and real-time analysis.
Rating: Greenlight.pngGreenlight.pngGreenlight.png Stable Release - Assessment Details

other releases

The CRS3 poster was designed by Hugo Costa, OWASP's graphical designer. It can be reused under a CC BY-ND license.

The large version has a 300 dpi resolution, big enough to be printed in A2, A1, or even A0 format. The format is the standard poster size format 500mm x 700mm (19.68in x 27.56in).