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.