URL spoofing bug involving Firefox's error pages and document.write

[jplopezy@xxxxxxxxx]

Application: Firefox 3.0.11 
OS: Windows XP - SP3
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1 - Description 
2 - Vulnerability 
3 - POC/EXPLOIT 
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Description 

This software is a popular web browser that supports multiple platforms as 
(windows,linux,macos).

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Vulnerability 

The bug is caused when you try to open a url with a invalid char, in this time, 
you can edit the error page, and make a "spoof".

This not would be important because when you make the spoof the "invalid web" 
is loading all time, but as firefox allow that you call the "stop" method of 
other page you can stop this.

The result of this is a fake page.
 
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 POC/EXPLOIT 
 
The poc is a simple script that have a window.open(), it calls the url with 
invalid char, the invalid char can be a "," or "%" is important that you add 
some "%20" for display a "white space" in the url.

http://es.geocities.com/jplopezy/firefoxspoofing.html
 
PD : I send this to bugzilla
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 Juan Pablo Lopez Yacubian