I was unable to Install properly OpenSuSE 11.3 with Plesk 10.1.1. This has forced me to install Ubuntu 10.04 LTS and since then also to (re)learn some basic stuff to secure my Linux server. Here are some of my How-To.

ModSecurity is an open source web application firewall (WAF) engine for Apache that is developed by Trustwave's SpiderLabs. It has a robust event-based programming language which provides protection from a range of attacks against web applications and allows for HTTP traffic monitoring, logging and real-time analysis. With over 10,000 deployments world-wide, ModSecurity is the most widely deployed WAF in existence.

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Install

Using the package manager

apt-get -y install libapache-mod-security

Configure

These are some directories that are needed by ModSecurity to work properly. Run all these commands before continuing:

chown www-data.www-data /var/asl/data/msa
chown www-data.www-data /var/asl/data/audit
chown www-data.www-data /var/asl/data/suspicious
chmod o-rx -R /var/asl/data/*
chmod ug+rwx -R /var/asl/data/* 
mkdir /var/asl/updates
mkdir /var/asl/rules/
mkdir /var/asl/rules/clamav

Initial setup

Create a new File

vi /etc/apache2/conf.d/00_modsecurity.conf

And put inside

<ifmodule mod_security2.c>
Include /etc/apache2/modsecurity.d/modsecurity_crs_10_config.conf
</ifmodule>

Then create new directory that will contains mod security rules

mkdir /etc/apache2/modsecurity.d/
vi /etc/apache2/modsecurity.d/modsecurity_crs_10_config.conf

Content of file modsecurity_crs_10_config.conf

Some default values to hide the server name and signature

 ServerTokens Prod
 ServerSignature Off
 TraceEnable Off

 SecRuleEngine On
 SecRequestBodyAccess On
 SecResponseBodyAccess On
 SecResponseBodyMimeType (null) text/html text/plain text/xml
 SecResponseBodyLimit 2621440
 SecServerSignature Apache
 SecComponentSignature 200911012341
 SecUploadDir /var/asl/data/suspicious
 SecUploadKeepFiles Off
 SecAuditEngine RelevantOnly
 SecAuditLogRelevantStatus "^(?:5|4(?!04))"
 SecAuditLogType Concurrent
 SecAuditLog logs/audit_log
 SecAuditLogParts ABIFHZ
 SecArgumentSeparator "&"
 SecCookieFormat 0
 SecRequestBodyInMemoryLimit 131072
 SecDataDir /var/asl/data/msa
 SecTmpDir /tmp
 SecAuditLogStorageDir /var/asl/data/audit
 SecResponseBodyLimitAction ProcessPartial

 Include /etc/apache2/modsecurity.d/gotroot/*asl*.conf

Getting Initial set of rules from Gotroot

Run these commands to install the latest free but delayed set of ModSecurity Rules from GotRoot.com

The last command restart apache,

cd /etc/apache2/modsecurity.d/gotroot
wget http://updates.atomicorp.com/channels/rules/delayed/modsec-2.5-free-latest.tar.gz
tar zxvf modsec-2.5-free-latest.tar.gz
mv modsec/* .
/etc/init.d/apache2 restart

Watch your logs to see if you have some warning/error like these. This is confirming that ModSecurity is working as expected

[Mon Feb 28 20:52:45 2011] [error] [client 195.8.45.152] 
ModSecurity: Warning. CC# match "\\d{13,16}" at RESPONSE_BODY.
[offset "15816"] [file "/etc/apache2/modsecurity.d/gotroot/11_asl_data_loss.conf"]
[line "33"] [id "340838"] [rev "2"]
[msg "Atomicorp.com - FREE UNSUPPORTED DELAYED FEED - WAF Rules:
Potential credit card number detected in output (not blocked)"]

You can always get new rules by visiting http://updates.atomicorp.com/channels/rules/delayed/