Getting Started With Mod_Security


Mod_Security is the most widely known and used server based Web Application Firewall but I had not had a chance to play with it so I decided to take sometime this weekend to build a website ( to test it.   Here is a small walk through on how I did it.

Base Server Install:

I used AWS Lightsail to build a webserver using Ubuntu 16.04,  Apache2,  LetsEncrypt , and this HTML5 Template.

Install and configure the website with these commands:

sudo apt update && sudo apt upgrade -y
sudo apt install apache2 git -y
sudo rm /var/www/html/index.html
sudo git clone /var/www/html/
sudo add-apt-repository ppa:certbot/certbot
sudo apt-get update
sudo apt-get install python-certbot-apache
sudo certbot

Mod_Security Install

Install Mod_Security with these commands:

sudo apt-get install libapache2-modsecurity
sudo cp /etc/modsecurity/modsecurity.conf-recommended /etc/modsecurity/modsecurity.conf

Move from logging to blocking move with these commands:

sudo nano /etc/modsecurity/modsecurity.conf
# Change SecRuleEngine DetectionOnly
SecRuleEngine On

It should look like this:Install the updated OWASP ModSecurity Core Rule Set:

sudo rm -rf /usr/share/modsecurity-crs
sudo git clone /usr/share/modsecurity-crs

Enable them in the apache config file:

sudo nano /etc/apache2/mods-enabled/security2.conf
     IncludeOptional /usr/share/modsecurity-crs/*.conf
     IncludeOptional /usr/share/modsecurity-crs/rules/*.conf

It should look like this:

Move the OWASP rules from logging to blocking:

cd /usr/share/modsecurity-crs
sudo cp crs-setup.conf.example crs-setup.conf
sudo nano crs-setup.conf

Comment Out: 
#SecDefaultAction "phase:1,log,auditlog,pass"
#SecDefaultAction "phase:2,log,auditlog,pass"

SecDefaultAction "phase:1,log,auditlog,deny,status:403"
SecDefaultAction "phase:2,log,auditlog,deny,status:403"

It should look like this:

Next restart apache to enable mod_security:

sudo systemctl restart apache2


To test I used burp suite to scan to generate plenty of “bad traffic”.

Run this to see what is being blocked in real time:

sudo tail -f /var/log/apache2/modsec_audit.log

Next Steps

Now that I have mod_security running I need to find a better logging solution.   So far I have quickly looked at waf-fle and auditconsole but they both look to be abandoned.  It looks like there are people who are doing a lot with ELK but I have not found anything solid yet.  I am really surprised there isn’t a ready made Dashboard but I will keep looking.


I have spent all of four hours playing with this on non-production traffic.  Please do not just install this in front of your website and then blame me when things break.


Overall with the help of @infosecdad  and @lojikil guiding me through some of the places where documentation is lacking it was fairly easy to get this setup and going.   If you have any questions please reach out to me on twitter at @JGamblin. 

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