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www.waraxe.us Forum Index -> Cross-site scripting aka XSS -> Help to evade xss filter...
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Help to evade xss filter...
PostPosted: Mon Feb 14, 2011 4:35 am Reply with quote
aritmos
Advanced user
Advanced user
 
Joined: Jul 21, 2008
Posts: 82
Location: Inside a salted MD5




I send this XSS:

"><script>alert('xss')</script><f

Browser you can see:

"><script>alert('xss')<%2Fscript><f

And source code generated:

<input name="query" value="&quot;&gt;&lt;script&gt;alert('xss')&lt;/script&gt;&lt;f" class="text text_query query" id="query" type="text">

how can i evade the filters?
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PostPosted: Mon Feb 14, 2011 5:41 pm Reply with quote
Cyko
Moderator
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Joined: Jul 21, 2009
Posts: 375




Problems:

1. Double quotes are converted to entities.
2. The < and > characters are also converted to entities.

Theirfore (too my knowledge) you can't brake out of the value attribute (in that format) - which is whats needed to execute/parse any JavaScript (as the value attribute can't execute/parse JavaScript on its own).

If the attribute was an on* (onclick, onhover etc.) attribute their would'nt be any problems (as their'd be no need to use double quotes or < and > characters) - infact it would be a breeze.

On a side note to the site owner - I assume the site is using htmlspecialchars(), I'd recommend to set the second paremeter to ENT_QUOTES to allow not only double quotes but single too (as currently its just converting double) - always a good idea to further migitate the risk of XSS attacks.

More info:

http://www.w3schools.com/tags/att_input_value.asp

http://ha.ckers.org/xss.html
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PostPosted: Tue Feb 15, 2011 8:55 am Reply with quote
aritmos
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Joined: Jul 21, 2008
Posts: 82
Location: Inside a salted MD5




then...is it imposible to do a xss injection?
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Help to evade xss filter...
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