Serious security Flaw in Microsoft Internet Explorer - Zone Spoofing

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Risk: POTENTIALLY HIGH.
Potentially allowing any possible action on the client machine, including 
reading any file, placing Trojan code or altering data.
The risk depends on the security settings in the 'Intranet zone'.

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Scope:
Client browser. Microsoft Internet explorer 4.x 5.x. (IE 6 seems to be not 
vulnerable).
OS versions scope not known. This vulnerablility was discoved on windows 
2000 SP2 with the latest security and office updates.

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Background:

Microsoft internet explorer security is dependant on different 'security 
zones'. These zones (Local Intranet zone and Internet zone) can have 
different security settings in regards to scripting and ActiveX execution. A 
lot of individuals and companies (including Microsoft) are depending on 
these zones to allow custom written activeX controls (unsigned and unsafe 
for scripting) to run on their internal intranet or network.
A flaw has been discovered in Internet Explorer that can bypass these zones 
and ‘fool’ the browser into believing an Internet site resides in the local 
intranet zone. This has as result that malicious website owners could 
potentially operate (and execute malicious code) in the users local intranet 
zone by luring surfers to their site with specially crafted URL’s.

In order for this Flaw to be dangerous, the user would have to have lower 
security settings in the intranet zone then in the Internet zone.

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Technical details:

Example:

An option in a basic authenticated site is to pass on a username (and/or 
password) in the URL like this:

http://mike@msdn.microsoft.com

Another possibility is to convert an IP address into a dotless IP address; 
such an address is also called a DWORD address (some proxy servers, routers 
or web servers do not allow this).

http://msdn.microsoft.com - IP: 207.46.239.122

Convert this IP address to a DWORD address:

207 * 16777216 		= 3472883712
46 * 65536  		= 3014656
239 * 256		= 61184
122 * 1			= 122
------------------------------------------------ +
			= 3475959674

This DWORD address can be used to visit the site like:

http://3475959674

If we combine the URL login option with the DWORD IP address we’ll get the 
following URL:

http://mike@3475959674

The browser still thinks we are in the internet zone as expected.

Now we change the @ sign to its ASCII equivalent (%40):


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http://mike%403475959674
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Using this link, the browser thinks the Internet site we are in is the local 
intranet zone!



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Disclosure details:

The flaw has been discovered by Michiel Kikkert from Kikkert Security and 
Microsoft was notified on the 26th of July.
Since then, Microsoft has been working hard to make core changes to Internet 
Explorer and to develop a patch to resolve this issue.

An official Microsoft patch that will fix this can be found at the following 
address:

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-051.asp

(URL may wrap)


Kind Regards,
Michiel Kikkert – security@kikkert.nl
Kikkert Security.

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