Ringzer0ctf — PHP Jail 1

Hello, this is a write-up for the PHP Jail 1 challenge from ringzer0ctf.

Before we begin with the challenge i want to share my discord server, i run a discord-based CTF platform. There you can find CTF challenges, resources, tools, write-ups from other online CTFs and much more.

Join NemesisCTF : https://discord.gg/fCtkmRX

First job we have to do is to connect to the challenge.

Now we have to analyze the source code.

We have to focus to function filter :

Function filter blocks other functions like open/exec/pass/system .. so we simply have to google. A simple google-fu like “php read file” give us this :

PHP readfile() Function

Let’s use this to grab the flag!

Bye.