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Re: [XHR] security issue with spec's "same-origin" and the Document pointer

From: Hallvord R. M. Steen <hallvord@opera.com>
Date: Sun, 23 Nov 2008 18:13:41 +0100
To: "Anne van Kesteren" <annevk@opera.com>, public-webapps@w3.org
Message-ID: <op.uk20s3nca3v5gv@hr-opera.oslo.opera.com>

On Fri, 21 Nov 2008 21:14:59 +0100, Anne van Kesteren <annevk@opera.com>  

>> var xhrConstructor = iframe.contentWindow.XMLHttpRequest;
>> iframe.src='http://attackee.example.com/';
>> .
>> .
>> var xhr = new xhrConstructor();
>> When the constructor is invoked here, the associated document of its  
>> associated window object is not safe to do same-origin comparisons  
>> against. I've tested this in the main 4 engines, and they all protect  
>> against this exploit but as far as I can see someone implementing the  
>> spec as it's written would end up vulnerable.
> Why would the SECURITY_ERR exception not be thrown during the open()  
> method invocation as the specification requires?

Because when you call "new xhrConstructor()" the document pointer is  
initialized *but at that point the document of the associated window  
originates from attackee.example.com*. If the script goes on to request  
content from this domain, the same-origin comparison against the document  
pointer would pass when it should in fact fail because the script itself  
is from a different origin.

Hallvord R. M. Steen
Core JavaScript tester, Opera Software
Opera - simply the best Internet experience
Received on Sunday, 23 November 2008 17:14:16 UTC

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