Category:OWASP ModSecurity Core Rule Set Project

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Further development of ModSecurity and the Core Rule Set occurs through mailing list discussions and occasional workshops, and suggestions for improvement are welcome. For more information, please [mailto:ryan.barnett@owasp.org contact us].


 * CRS mailing list (this is the main list)
 * ModSecurity mailing list

ModSecurity Core Rule Set Project

Want to help?
CRS Development

The CRS project is always on the lookout for volunteers who are interested in contributing. We need help in the following areas:


 * Documentation of the CRS
 * New Detection Methods
 * Updates to existing rules



Related resources
OWASP Resources


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Download
Current Stable Release is always available here:

https://sourceforge.net/projects/mod-security/files/modsecurity-crs/0-CURRENT/

SVN Repository is here:

http://mod-security.svn.sourceforge.net/viewvc/mod-security/crs/

CRS Releases are signed by Ryan Barnett. These public keys are available via most PGP key server mirrors.

https://pgp.webtru.st/pks/lookup?op=get&search=0xA5C6BF964EF28948

Bug Tracker
JIRA Ticket System:

https://www.modsecurity.org/tracker/browse/CORERULES

Demo
ModSecurity CRS Demonstration/Smoketest page:

http://www.modsecurity.org/demo/

Installation
Quick Start

Core Rule Set Quick Setup

=
============

To activate the rules for your web server installation:

1) The modsecurity_crs_10_config.conf includes management rules and directives    that can control important CRS functions. Pay attention to     the SecRuleEngine setting (On by default) and that the SecDefaultAction     directive is set to "pass".  The 49 inbound blocking and 59 outbound blocking     rules files use the "block" action which     inherits this setting.  The effectively means that you can toggle the     SecDefaultAction setting to decide if you would like to deny on an     anomaly scoring/correlation match.

Update the PARANOID_MODE variable setting if you want to become more aggressive in your detection. Caution - this will cause more false positives.

Should also update the appropriate anomaly scoring levels that will be propagated to the inbound/outbound blocking files.

Update the TX policy settings for allowed Request Methods, File Extensions, etc...

2) Add the following line to your httpd.conf (assuming you've placed the rule files into conf/modsecurity_crs/):

 Include conf/modsecurity_crs/*.conf Include conf/modsecurity_crs/base_rules/*.conf 

3) Restart web server.

4) Make sure your web sites are still running fine.

5) Simulate an attack against the web server. Then check    the attack was correctly logged in the Apache error log,     ModSecurity debug log (if you enabled it) and ModSecurity     audit log (if you enabled it).

Documentation
= Rule Documentation Template = Each ModSecurity Rule in the CRS has an individual rule description page based on the following template file:

http://www.owasp.org/index.php/ModSecurity_CRS_Rule_Description_Template


 * Project participants are encouraged to copy this template and create landing pages for each CRS rule
 * Use this template and create a new page using the following format - http://www.owasp.org/index.php?title=ModSecurity_CRS_RuleID-XXXXX (where XXXXX is the CRS ruleID)

Example:

http://www.owasp.org/index.php/ModSecurity_CRS_RuleID-960911

= ModSecurity Core Rule Set (CRS) =

The ModSecurity Core Rule Set is provided to you under the terms and conditions of GPL version 2

This directory contains the files for Core ModSecurity Rule Set The rules are compatible with ModSecurity 2.5 (as of version 1.4.3)

= Overview = Using ModSecurity requires rules. In order to enable users to take full advantage of ModSecurity immediately, Trustwave is providing a free Core rule set. 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. This is what we call "Attack Payload Detection."

Keep in mind that a predefined rule set is only part of the work required to protect your web site. We strongly urge you to consult Ivan Ristic's book, "ModSecurity Handbook" http://store.feistyduck.com/products/modsecurity-handbook and the ModSecurity Reference Manual - http://www.modsecurity.org/documentation/. The CRS is heavily commented to allow it to be used as a step-by-step deployment guide for ModSecurity.

For more information refer to the OWASP Core Rule Set Project page at http://www.owasp.org/index.php/Category:OWASP_ModSecurity_Core_Rule_Set_Project

Core Rules Mail-list - Suscribe here: https://lists.owasp.org/mailman/listinfo/owasp-modsecurity-core-rule-set Archive: https://lists.owasp.org/pipermail/owasp-modsecurity-core-rule-set/

= CRS 2.0 Design Concepts =

CRS < 2.0 - Self-Contained Rules
Older (<2.0) CRS used individual, “self-contained” actions in rules - If a rule triggered, it would either deny or pass and log - No intelligence was shared between rules Not optimal from a rules management perspective (handling false positives/exceptions) - Editing the regex could blow it up - Typical method was to copy/paste rules into custom rules files and then edit rule logic and disable core rule ID. - Heavily customized rules were less likely to be updated by the user Not optimal from a security perspective - Not every site had the same risk tolerance - Lower severity alerts were largely ignored - Individual low severity alerts are not important but several low severity events in the same transaction are.

= CRS 2.0 - Collaborative Detection =

Rules - Detection and Management
Rules logic has changed by decoupling the inspection/detection from the blocking functionality - Rules log.pass and set transactional variables (tx) to track anomaly scores and to   store meta-data about the rule match - This TX rule match data can be used by other 3rd party rules (converter Emerging Threats  Snort web attack rules) to more accurately correlate identified attacks with their attack vector locations. - TX data of previous strong rule matches can also be used to conditionally apply weaker signatures that normally would have a high fasle positive rate. - Rules also increase anomaly scores for both the attack category and global score which allows users to set a threshold that is appropriate for them. - This also allows several low severity events to trigger alerts while individual ones are suppressed. - Exceptions may be handled by either increasing the overall anomaly score threshold, or  by adding rules to a local custom exceptions file where TX data of previous rule matches may be inspected and anomaly scores re-adjusted based on the false positive criteria.

User can now globally update which variables to inspect and the anomaly score settings in the modsecurity_crs_10_config.conf file. - PARANOID_MODE setting which will apply rules to locations that have a higher false positive rate - INBOUND_ANOMALY_SCORE setting will be populated in the inbound blocking file and if a transaction score at the end of phase:2 is equal to or greater than this number, it will be denied. - OUTBOUND_ANOMALY_SCORE setting will be populated in the outbound blocking file and it a transaction score at the end of phase:4 is equal to or greater than this number, it will be denied.

= Inbound/Outbound Blocking = The CRS rules themselves are configured with the pass action, which allows all the rules to be processed and for the proposed anomaly scoring/collaborative detection concept to work. The inbound/outbound anomaly score levels may be set in the modsecurity_crs_10_config.conf file. These scores will be evaluated in the modsecurity_crs_49_inbound_blocking.conf and modsecurity_crs_59_outbound_blocking.conf files.

= Alert Management - Correlated Event Creation = One of the top feedback items we have heard is that the CRS events in the Apache error_log file were very chatty. This was due to each rule triggering its own error_log entry. What most people wanted was for 1 correlated event to be generated that would give the user a higher level determination as to what the event category was.

To that end- each CRS rule will generate an audit log event Message entry but they will not log to the error_log on their own. These rules are now considered basic or reference events and may be reviewed in the audit log if the user wants to see what individual events contributed to the overall anomaly score and event designation.

= Inbound/Outbound Correlation = After the transaction has completed (in the logging phase), the rules in the base_rules/modsecurity_crs_60_correlation.conf file will conduct further post-processing by analyzing any inbound events with any outbound events in order to provide a more intelligent/priority correlated event.

- Was there an inbound attack? - Was there an HTTP Status Code Error (4xx/5xx level)? - Was there an application information leak?

If an inbound attack was detected and either an outbound application status code error or infolead was detected, then the overall event severity is raised -

- 0: Emergency - is generated from correlation where there is an inbound attack and an outbound leakage. - 1: Alert - is generated from correlation where there is an inbound attack and an  outbound application level error.

= Core Rule Set Content = In order to provide generic web applications protection, the Core Rule Set uses the following techniques:

HTTP Protocol Validation and Protection
Detecting violations of the HTTP protocol and a locally defined usage policy. This first line of protection ensures that all abnormal HTTP requests are detected. This line of defense eliminates a large number of automated and non targeted attacks as well as protects the web server itself.

base_rules/modsecurity_crs_20_protocol_violations.conf
Protocol vulnerabilities such as Response Splitting, Request Smuggling, Premature URL ending - Content length only for non GET/HEAD methods - Non ASCII characters or encoding in headers - Valid use of headers (for example, content length is numerical) - Proxy Access

base_rules/modsecurity_crs_21_protocol_anomalies.conf
Attack requests are different due to automation - Missing headers such as Host, Accept, User-Agent - Host is an IP address (common worm propagation method)

base_rules/modsecurity_crs_23_request_limits.conf
Policy is usually application specific - Some restrictions can usually be applied generically - White lists can be build for specific environments Limitations on Sizes - Request size, Upload size - # of parameters, length of parameter

base_rules/modsecurity_crs_30_http_policy.conf
Items that can be allowed or restricted - Methods - Allow or restrict WebDAV, block abused methods such as CONNECT, TRACE or DEBUG - File extensions – backup files, database files, ini files - Content-Types (and to some extent other headers)

Automation Detection
Automated clients are both a security risk and a commercial risk. Automated crawlers collect information from your site, consume bandwidth and might also search for vulnerabilities on the web site. Automation detection is especially useful for generic detection of comments spam.

Detecting bots, crawlers, scanners and other surface malicious activity. Not aimed against targeted attacks, but against general malicious internet activity - Offloads a lot of cyberspace junk & noise - Effective against comment spam - Reduce event count

base_rules/modsecurity_crs_35_bad_robots.conf
Detection of Malicious Robots - Unique request attributes: User-Agent header, URL, Headers - RBL Check of IP addresses - Detection of security scanners - Blocking can confuse security testing software (WAFW00f)

optional_rules/modsecurity_crs_42_comment_spam.conf
This rules file is only relevant if you are concerned about comment SPAM attacks. The rules file will run an RBL check against the source IP address at SPAMHAUS and will cache the response for 1 day. If the client sends subsequent requests, it will be denied without having to re-run an RBL check.

This file will also look for comment SPAM posting attacks which submit URL links.

Common Web Attacks Protection
Common Web Attacks Protection Rules on the second level address the common web application security attack methods. These are the issues that can appear in any web application. Some of the issues addressed are:

- SQL Injection - Cross-Site Scripting (XSS) - OS Command execution - Remote code inclusion - LDAP Injection - SSI Injection - Information leak - Buffer overflows - File disclosure

base_rules/modsecurity_crs_40_generic_attacks.conf
- OS command injection and remote command access - Remote file inclusion - Session Fixation

optional_rules/modsecurity_crs_40_experimental.conf
The rules in this file are considered BETA quality as they have not been rigorously tested. They attempt to address advanced attacks such as HTTP Parameter Pollution or use new rule features or techniques.

base_rules/modsecurity_crs_42_tight_security.conf
This rules file attempts to identify all directory traversal variations. It is prone to a high level of false positives so set PARANOID_MODE if you want to run these rules.

base_rules/modsecurity_crs_41_sql_injection.conf
- SQL injection and blind SQL injection

base_rules/modsecurity_crs_41_xss.conf
- Cross site scripting (XSS)

base_rules/modsecurity_crs_41_phpids_filters.conf
SpiderLabs received authorization from PHPIDS (http://phpids.net/) to convert their rules and include them in the CRS - Thanks to Mario Heiderich

Converted version of PHPIDS Converter.php functionality. https://svn.php-ids.org/svn/trunk/lib/IDS/Converter.php These rules look for common evasion tactics.

Converted version of PHPIDS default_filters.xml data. https://svn.php-ids.org/svn/trunk/lib/IDS/default_filter.xml

These rules are *not* PHP-specifc and apply to *all* web platforms
- Filters are heavily tested by the community and updated frequently - ~70 regular expression rules to detect common attack payloads - XSS - SQL Injection - RFI

optional_rules/modsecurity_crs_46_et_web_rules.conf
Due to the high number of rules and the possible impact on performance, these rules have been placed in the optional_rules directory.

SpiderLabs received authorization from ET to convert their Snort rules and include them in the CRS http://www.emergingthreats.net/

Converted the following ET Snort rule files - emerging-web_server.rules - emerging-web_specific_apps.rules

Identifying attacks against known web vulnerabilities does have value - Raised threat level - If done correctly, lessens false positives

The issue to overcome is that the PCRE RegExs used in the rules are pretty poor. What we want to do is to combine the *what* of our generic attack payload detection (attack payloads) with the *where* (attack vector - URL + Parameter Name) of the ET known vuln data. The approach we took was to have most of the ET rules look for the attack vector data and then simply check all saved TX data for a corresponding attack vector match.

Trojan Protection
ModSecurity Core Rule Set detects access to back doors installed on a web server. This feature is very important in a hosting environment when some of this backdoors may be uploaded in a legitimate way and used maliciously. In addition the Core Rule Set includes a hook for adding an Anti-Virus program such as ClamAV for checking file uploads.

base_rules/modsecurity_crs_45_trojans.conf
- Check uploading of http backdoor page - Access detection - Known signatures (x_key header) - Generic file management output (gid, uid, drwx, c:\)

InfoLeakages
If all fails, the Core Rule Set will detect errors sent by the web server. Detecting and blocking errors prevents attackers from collecting reconnaissance information about the web application and also server as a last line of defense in case an attack was not detected eariler.

base_rules/modsecurity_crs_50_outbound.conf
- HTTP Error Response Status Codes - SQL Information Leakage - Stack Dumps - Source Code Leakage

Request Header Tagging
This concept is similar to anti-SPAM SMTP apps that will add additional mime headers to emails providing the SPAM detection analysis information. The CRS is attempting to mimic this concept at the HTTP layer by adding additional request headers that provide insight into any ModSecurity events that may have triggered during processing. The advantage of this approach is that it allows a WAF to be in a detection-only mode while still providing attack data to the destination application server. The recieving app server may then inspect the WAF request headers and make a determination whether or not to process the transaction. This concept is valuable in distributed web environments and hosting architectures where a determination to block may only be appropriate at the destination app server.

optional_rules/modsecurity_crs_49_header_tagging.conf
This rules file will take all of the TX attack variable data and populate Apache ENV variables that Apache can then use to add X-WAF-Event request header data to the request.

Example showing the consolidated X-WAF-Events and X-WAF-Score data -

GET /path/to/foo.php?test=1%27%20or%20%272%27=%272%27;-- HTTP/1.1 Host: www.example.com User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.5) Gecko/20091109 Ubuntu/9.10 (karmic) Firefox/3.5.5 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 X-WAF-Events: TX: / 999935-Detects common comment types-WEB_ATTACK/INJECTION-ARGS:test, TX:999923-Detects JavaScript location/document property access and window access obfuscation-WEB_ATTACK/INJECTION-REQUEST_URI_RAW, TX:950001- WEB_ATTACK/SQL_INJECTION-ARGS:test X-WAF-Score: Total=48; sqli=2; xss= Connection: Keep-Alive

Presentations and Whitepapers
Current CRS v2 presented at AppSec DC 2009.

Ofer Shezaf's presentation and whitepaper on the Core Rule Set v1 presented at 6th OWASP AppSec conference in Milan, Italy, in May 2007

Related Projects
ModSecurity-Open Source Web Application Firewall OWASP Securing WebGoat using ModSecurity OWASP AppSensor Project

Latest News and Mail List
Current Stable Version CRS 2.0.8

-- Version 2.0.8 - 08/27/2010 --

Improvements: - Updated the PHPIDS filters - Updated the SQL Injection filters to detect boolean attacks (1<2, foo == bar, etc..) - Updated the SQL Injection filters to account for different quotes - Added UTF-8 encoding validation support to the modsecurity_crs_10_config.conf file - Added Rule ID 950109 to detect multiple URL encodings - Added two experimental rules to detect anomalous use of special characters

Bug Fixes: - Fixed Encoding Detection RegEx (950107 and 950108) - Fixed rules-updater.pl script to better handle whitespace https://www.modsecurity.org/tracker/browse/MODSEC-167 - Fixed missing pass action bug in modsecurity_crs_21_protocol_anomalies.conf https://www.modsecurity.org/tracker/browse/CORERULES-55 - Fixed the anomaly scoring in the modsecurity_crs_41_phpids_filters.conf file https://www.modsecurity.org/tracker/browse/CORERULES-54 - Updated XSS rule id 958001 to improve the .cookie regex to reduce false postives https://www.modsecurity.org/tracker/browse/CORERULES-29

-- Version 2.0.7 - 06/4/2010 --

Improvements: - Added CSRF Protection Ruleset which will use Content Injection to add javascript to  specific outbound data and then validate the csrf token on subsequent requests. - Added new Application Defect Ruleset which will identify/fix missing HTTPOnly cookie flags - Added Experimental XSS/Missing Output Escaping Ruleset which looks for user supplied data being echoed back to user unchanged. - Added rules-updater.pl script and configuration file to allow users to automatically download CRS rules from the CRS rules repository. - Added new SQLi keyword for ciel and reverse functions. - Updated the PHPIDS filters

Bug Fixes: - Fixed false positives for Request Header Name matching in the 30 file by   adding boundary characters. - Added missing pass actions to @pmFromFile prequalifier rules - Added backslash to SQLi regex https://www.modsecurity.org/tracker/browse/CORERULES-41 - Fixed hard coded anomaly score in PHPIDS filter file https://www.modsecurity.org/tracker/browse/CORERULES-45 - Fixed restricted_extension false positive by adding boundary characters

-- Version 2.0.6 - 02/26/2010 --

Bug Fixes: - Added missing transformation functions to SQLi rules. https://www.modsecurity.org/tracker/browse/CORERULES-32 - Fixed duplicate rule IDs. https://www.modsecurity.org/tracker/browse/CORERULES-33 - Fixed typo in @pmFromFile in the Comment SPAM rules https://www.modsecurity.org/tracker/browse/CORERULES-34 - Added macro expansion to Restricted Headers rule https://www.modsecurity.org/tracker/browse/CORERULES-35 - Fixed misspelled SecMarker https://www.modsecurity.org/tracker/browse/CORERULES-36 - Fixed missing chain action in Content-Type header check https://www.modsecurity.org/tracker/browse/CORERULES-37 - Update phpids filters to use pass action instead of block

-- Version 2.0.5 - 02/01/2010 --

Improvements: - Removed previous 10 config files as they may conflict with local customized Mod configs. - Added a new 10 config file that allows the user to globally set TX variables to turn on/off PARANOID_MODE inspection, set anomaly score levels and http policies. Must have ModSecurity 2.5.12 to use the macro expansion in numeric operators. - Added Rule Logic and Reference links to rules descriptions. - Added Rule IDs to all rules. - Added tag data mapping to new OWASP Top 10 and AppSensor Projects, WASC Threat Classification - Removed Apache limit directives from the 23 file - Added macro expansion to 23 file checks. - Added @pmFromFile check to 35 bad robots file - Added malicious UA strings to 35 bad robots check - Created an experimental rules file - Updated HTTP Parameter Pollution (HPP) rule logic to concat data into a TX variable for inspection - Removed TX inspections for generic attacks and reverted to standard ARGS inspection https://www.modsecurity.org/tracker/browse/MODSEC-120 - Updated the variable list for standard inspections (ARGS|ARGS_NAMES|XML:/*) and moved the other variables to the PARANOID list (REQUEST_URI|REQUEST_BODY|REQUEST_HEADERS|TX:HPP_DATA) - Moved converted ET Snort rules to the /optional_rules directory - Created a new Header Tagging ruleset (optional_rules) that will add matched rule data to the request headers. - Updated Inbound blocking conf file to use macro expansion from the 10 config file settings - Added separate anomaly scores for inbound, outbound and total to be evaluated for blocking. - Updated the regex logic in the (1=1) rule to factor in quotes and other logical operators. - Updated the SPAMMER RBL check rules logic to only check once per IP/Day. - Added new outbound malware link detection rules.

Bug Fixes: - Removed Non-numeric Rule IDs https://www.modsecurity.org/tracker/browse/CORERULES-28 - Updated the variable list on SQLi rules. - Fixed outbound @pmFromFile action from allow to skipAfter to allow for outbound anomaly scoring and blocking

-- Version 2.0.4 - 11/30/2009 --

Improvements:

- Updated converted PHPIDS signatures (https://svn.php-ids.org/svn/trunk/lib/IDS/default_filter.xml) - Updated PHPIDS rules logic to first search for payloads in ARGS and then if there is no match found then search more generically in request_body|request_uri_raw - Updated PHPIDS rules logic to only set TX variables and to not log. This allows for more clean exceptions in the 48 file which can then expire/delete false positive TX matches and adjust the anomaly scores. These rules will then inspect for any TX variables in phase:5 and create appropriate alerts for any variable matches that exist.

Bug Fixes:

- Added Anomaly Score check to the 60 correlation file to recheck the anomaly score at the end of  phase:4 which would allow for blocking based on information leakage issues.

Project Mail List Subscribe here [mailto:owasp-modsecurity-core-rule-set@lists.owasp.org Use here]

Contributors, Users and Adopters
Project Leader

Ryan Barnett

Project Contributors

Brian Rectanus

The Core Rule Set (CRS) project is sponsored by:

Project Users

WASC Distributed Open Proxy Honeypot Project uses the Core Rule Set - http://projects.webappsec.org/Distributed-Open-Proxy-Honeypots

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

Project About
''The CRS is an open source rule set licensed under GPLv2. ModSecurity Core Rule Set works with ModSecurity 2.5 and above.''