Secure Your Apache With mod_security
Version 1.0
Author: Falko Timme
This article shows how to install and configure mod_security. mod_security is an Apache module (for Apache 1 and 2) that provides intrusion detection and prevention for web applications. It aims at shielding web applications from known and unknown attacks, such as SQL injection attacks, cross-site scripting, path traversal attacks, etc.
In the first chapter I will show how to install mod_security on Debian Sarge, Ubuntu 6.06 LTS (Dapper Drake), and on Fedora Core 5, and in the second chapter I will describe how to configure Apache for mod_security which is independent from the distribution you're using.
I want to say first that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!
1 Installation
1.1 Debian Sarge
mod_security is available as a Debian package in the default Debian repositories, therefore the installation is as simple as this:
apt-get install libapache2-mod-security
a2enmod mod-security
/etc/init.d/apache2 force-reload
1.2 Ubuntu 6.06 LTS (Dapper Drake)
The installation is exactly the same as on Debian Sarge:
apt-get install libapache2-mod-security
a2enmod mod-security
/etc/init.d/apache2 force-reload
1.3 Fedora Core 5
On Fedora, you can install and activate mod_security like this:
yum install mod_security
/etc/init.d/httpd restart
You should now find the file /etc/httpd/conf.d/mod_security.conf which already contains a basic mod_security configuration:
vi /etc/httpd/conf.d/mod_security.conf
# Example configuration file for the mod_security Apache module
LoadModule security_module modules/mod_security.so
<IfModule mod_security.c>
# Turn the filtering engine On or Off
SecFilterEngine On
# The audit engine works independently and
# can be turned On of Off on the per-server or
# on the per-directory basis
SecAuditEngine RelevantOnly
# Make sure that URL encoding is valid
SecFilterCheckURLEncoding On
# Unicode encoding check
SecFilterCheckUnicodeEncoding On
# Only allow bytes from this range
SecFilterForceByteRange 1 255
# Cookie format checks.
SecFilterCheckCookieFormat On
# The name of the audit log file
SecAuditLog logs/audit_log
# Should mod_security inspect POST payloads
SecFilterScanPOST On
# Default action set
SecFilterDefaultAction "deny,log,status:406"
# Simple example filter
# SecFilter 111
# Prevent path traversal (..) attacks
# SecFilter "\.\./"
# Weaker XSS protection but allows common HTML tags
# SecFilter "<( |\n)*script"
# Prevent XSS atacks (HTML/Javascript injection)
# SecFilter "<(.|\n)+>"
# Very crude filters to prevent SQL injection attacks
# SecFilter "delete[[:space:]]+from"
# SecFilter "insert[[:space:]]+into"
# SecFilter "select.+from"
# Require HTTP_USER_AGENT and HTTP_HOST headers
SecFilterSelective "HTTP_USER_AGENT|HTTP_HOST" "^$"
# Only accept request encodings we know how to handle
# we exclude GET requests from this because some (automated)
# clients supply "text/html" as Content-Type
SecFilterSelective REQUEST_METHOD "!^GET$" chain
SecFilterSelective HTTP_Content-Type "!(^$|^application/x-www-form-urlencoded$|^multipart/form-data)"
# Require Content-Length to be provided with
# every POST request
SecFilterSelective REQUEST_METHOD "^POST$" chain
SecFilterSelective HTTP_Content-Length "^$"
# Don't accept transfer encodings we know we don't handle
# (and you don't need it anyway)
SecFilterSelective HTTP_Transfer-Encoding "!^$"
# Some common application-related rules from
# http://modsecrules.monkeydev.org/rules.php?safety=safe
#Nuke Bookmarks XSS
SecFilterSelective THE_REQUEST "/modules\.php\?name=Bookmarks\&file=(del_cat\&catname|del_mark\&markname|edit_cat\&catname|edit_cat\&catcomment|marks\&catname|uploadbookmarks\&category)=(<[[:space:]]*script|(http|https|ftp)\:/)"
#Nuke Bookmarks Marks.php SQL Injection Vulnerability
SecFilterSelective THE_REQUEST "modules\.php\?name=Bookmarks\&file=marks\&catname=.*\&category=.*/\*\*/(union|select|delete|insert)"
#PHPNuke general XSS attempt
#/modules.php?name=News&file=article&sid=1&optionbox=
SecFilterSelective THE_REQUEST "/modules\.php\?*name=<[[:space:]]*script"
# PHPNuke SQL injection attempt
SecFilterSelective THE_REQUEST "/modules\.php\?*name=Search*instory="
#phpnuke sql insertion
SecFilterSelective THE_REQUEST "/modules\.php*name=Forums.*file=viewtopic*/forum=.*\'/"
# WEB-PHP phpbb quick-reply.php arbitrary command attempt
SecFilterSelective THE_REQUEST "/quick-reply\.php" chain
SecFilter "phpbb_root_path="
#Topic Calendar Mod for phpBB Cross-Site Scripting Attack
SecFilterSelective THE_REQUEST "/calendar_scheduler\.php\?start=(<[[:space:]]*script|(http|https|ftp)\:/)"
# phpMyAdmin: Safe
#phpMyAdmin Export.PHP File Disclosure Vulnerability
SecFilterSelective SCRIPT_FILENAME "export\.php$" chain
SecFilterSelective ARG_what "\.\."
#phpMyAdmin path vln
SecFilterSelective REQUEST_URI "/css/phpmyadmin\.css\.php\?GLOBALS\[cfg\]\[ThemePath\]=/etc"
</IfModule>
|
You can keep this configuration, but to get a better understanding of what mod_security can do, you should comment out the <IfModule mod_security.c>...</IfModule> part, restart Apache, and follow chapter 2. Afterwards you can create your own mod_security ruleset, or just switch back to this one.