How I secured my server with Fail2Ban.

The other day I received a lot of alerts from the service I use to monitor the uptime of my blogs, all of them were down without an apparent reason. My blogs are hosted in a virtual private server configured with just a basics configuration, a LAMP server running in Ubuntu, no Webmin, no PhpMyAdmin, just the basic stack. Basics are the best, but that’s a topic for another post.

No worries, I have a solution for these kind of situations…

Yes, I’m not a pro backend developer, and as you can expect, it didn’t work. So I tried another restart. Nothing happened. $#%£!

Yes! I had a problem and I didn’t know a s*** about it. First thing, I connected to the server through SSH and I looked what was happening. It seemed Apache was down just a few seconds after a restart. Something was affecting it.

How did I know what was crashing my Apache? Logs! If something was happening, I’m sure it was written in the logs. So…

This gave me more information. Somebody was stacking my Apache and crashing it. I was being a victim of an xmlrpc DDOS attack. My logs had a lot of lines like this:

I had to put all my knowledge in backend security to work. Battle had started.

I know there are a lot of ways to block this kind of DDoS attacks but I read something about Fail2Ban and I wanted to test it against this thread. Fail2Ban is a tool that reads apache logs and if it detects something weird with an IP it blocks this IP using iptables. I installed it like this:

Then I created this file /etc/fail2ban/filter.d/wordpress.conf and I put this to create the filter definition:

I needed to add the filter to the jail, to do that I created this file /etc/fail2ban/jail.d/wordpress.conf with this information:

With that configuration, Fail2Ban will looked in apache2 logs for the filter to match a request every 3600 seconds, if it happened, then the IP would be banned for 86400 seconds using iptables.

That’s all, I just restarted Fail2Ban like this:

It didn’t take too much time to start watching logs with IPs banned. Yay!