| Overview ModSecurity™ is a web application firewall engine that provides very little protection on its own. In order to become useful, ModSecurity™ must be configured with rules. In order to enable users to take full advantage of ModSecurity™ out of the box, Trustwave's SpiderLabs is providing a free certified rule set for ModSecurity™ 2.x. Unlike intrusion detection and prevention systems, which rely on signatures specific to known vulnerabilities, the Core Rules provide generic protection from unknown vulnerabilities often found in web applications, which are in most cases custom coded. The Core Rules are heavily commented to allow it to be used as a step-by-step deployment guide for ModSecurity™. Core Rules Content In order to provide generic web applications protection, the Core Rules use the following techniques:
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SVN Repository is here:
http://mod-security.svn.sourceforge.net/viewvc/mod-security/crs/
Sync with SVN:
svn co https://mod-security.svn.sourceforge.net/svnroot/mod-security/crs/trunk
crs
CRS Releases are signed by Ryan Barnett. These public keys are available via most PGP key server mirrors.
http://pgp.mit.edu:11371/pks/lookup?op=vindex&search=0xC976607D9624FCD2
Manual Downloading: You can always download the latest CRS version here -
https://sourceforge.net/projects/mod-security/files/modsecurity-crs/0-CURRENT/
Automated Downloading: Use the rules-updater.pl script in the CRS /util directory
http://mod-security.svn.sourceforge.net/viewvc/mod-security/crs/
Sync with SVN:
svn co https://mod-security.svn.sourceforge.net/svnroot/mod-security/crs/trunk
crs
CRS Releases are signed by Ryan Barnett. These public keys are available via most PGP key server mirrors.
http://pgp.mit.edu:11371/pks/lookup?op=vindex&search=0xC976607D9624FCD2
Manual Downloading: You can always download the latest CRS version here -
https://sourceforge.net/projects/mod-security/files/modsecurity-crs/0-CURRENT/
Automated Downloading: Use the rules-updater.pl script in the CRS /util directory
- Get a list of what the repository contains:
$ ./rules-updater.pl -rhttp://www.modsecurity.org/autoupdate/repository/ -l
Repository: http://www.modsecurity.org/autoupdate/repository
modsecurity-crs {
2.0.0: modsecurity-crs_2.0.0.zip
2.0.1: modsecurity-crs_2.0.1.zip
2.0.2: modsecurity-crs_2.0.2.zip
2.0.3: modsecurity-crs_2.0.3.zip
2.0.4: modsecurity-crs_2.0.4.zip
2.0.5: modsecurity-crs_2.0.5.zip
2.0.6: modsecurity-crs_2.0.6.zip
2.0.7: modsecurity-crs_2.0.7.zip
2.0.8: modsecurity-crs_2.0.8.zip
2.0.9: modsecurity-crs_2.0.9.zip
2.1.0: modsecurity-crs_2.1.0.zip
}
- Get the latest stable version of "modsecurity-crs":
$ ./rules-updater.pl -rhttp://www.modsecurity.org/autoupdate/repository/ -prules -Smodsecurity-crs
Fetching: modsecurity-crs/modsecurity-crs_2.1.0.zip ...
$ ls -R rules
modsecurity-crs
rules/modsecurity-crs:
modsecurity-crs_2.1.0.zip modsecurity-crs_2.1.0.zip.sig
JIRA Ticket System:
https://www.modsecurity.org/tracker/browse/CORERULES
https://www.modsecurity.org/tracker/browse/CORERULES
ModSecurity CRS Demonstration/Smoketest page:
http://www.modsecurity.org/demo/
http://www.modsecurity.org/demo/
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/):
<IfModule security2_module>
Include conf/modsecurity_crs/*.conf
Include conf/modsecurity_crs/base_rules/*.conf
</IfModule>
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).
ModSecurity Blog Posts
http://blog.spiderlabs.com/modsecurity/- ModSecurity Advanced Topic of the Week: Traditional vs. Anomaly Scoring Detection Modes
- ModSecurity Advanced Topic of the Week: Exception Handling
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)
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 2This 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-handbookand 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-setArchive: 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 logNot optimal from a rules management perspective (handling false positives/exceptions)
- No intelligence was shared between rules
- Editing the regex could blow it upNot optimal from a security perspective
- 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 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 toUser can now globally update which variables to inspect and the anomaly score settings in the modsecurity_crs_10_config.conf file.
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.
- 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.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?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 -
- Was there an HTTP Status Code Error (4xx/5xx level)?
- Was there an application information leak?
- 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_converter.conf
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 HeiderichConverted version of PHPIDS Converter.php functionality. https://svn.php-ids.org/svn/trunk/lib/IDS/Converter.phpThese 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_sql_injection.conf
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.rulesIdentifying attacks against known web vulnerabilities does have value
- emerging-web_specific_apps.rules
- Raised threat levelThe 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.
- If done correctly, lessens false positives
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
