Warning: long read....

I got a call this morning from a client who was panicking about not being able to login to his web panel.

So I went to the web panel and tried to login and was just redirected back to the login page. No errors or anything (at least visible on the page). Went looking for an error_log file and found it.

It turns out there was an error was showing: Disk quota exceeded.

So I went into the cPanel and checked, he used about 16GB out of 100GB and that got me confused. So I looked around and found out he was using about 510000/500000 inodes.

Went looking trough FTP to see where he has so many files and try and remove some.

Well it turns out that there were about 7 injected websites (warez, online casino, affiliate one etc) and a full hacking web panel on his FTP. After detailed analysis some who actually built the site (I just maintain some parts) made an upload form available to public with any checks on it. Meaning anyone could upload whatever they wanted and the form would allow it.

The worst part is that the client is not allowing us to secure the form with some sort of login or remove it completely (the best option) as it is not really needed but he uses it to upload some pdf catalogs or something.

TL; DR;
Old programmer created an upload form that was accessible to anyone on the web without adding any security or check as to see what kind of files was getting uploaded. Which lead to having maximum number on inodes used on server and client being unable to login.

Side note:
And ofc I had to go and fix the mess behind him again, even though he stopped working a long time ago and I started just recently and have been having nightmares of this project.