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A  U  S  C  E  R  T                                           A  L  E  R  T

                       AL-2004.043 -- AUSCERT ALERT
         Microsoft Internet Explorer DHTML Edit Control Cross-site
                          Scripting Vulnerability
                             20 December 2004

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        AusCERT Alert Summary
        ---------------------

Product:           Microsoft Internet Explorer
Operating System:  Windows
Impact:            Provide Misleading Information
                   Access Privileged Data
Access:            Remote/Unauthenticated

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PROBLEM:  

	A vulnerability in Internet Explorer allows an attacker to open a 
	window to a trusted web site, and then execute arbitrary scripted 
	content in the security context of the trusted site.

	The vulnerability is located in Internet Explorer's DHTML Edit ActiveX 
	control, which is enabled by default.

	Secunia has constructed a demonstration of this vulnerability. [1]	


PRODUCTS:

	Microsoft Internet Explorer 6.0 on Windows XP and XP Service Pack 2 are
	confirmed vulnerable.

	Internet Explorer 5 and other Windows versions are also suspected to be
	vulnerable, but this has not yet been confirmed.


IMPACT:

	When a trusted web site is opened from a malicious web page, an attacker
	can execute arbitrary scripts in the context of the trusted site.

	This vulnerability can be used for example to replace the trusted web 
	page contents with content of the attackers' choice, while still 
	displaying the SSL golden padlock, original domain name and valid 
	authentication credentials.

	This may convince a user to provide a password or other sensitive 
	information to the attacker, instead of to the trusted site.

	AusCERT advises that proof of concept code has been published for this 
	vulnerability. It is anticipated that the vulnerability may be used in 
	conjunction with fake emails appearing to come from financial 
	institutions in order to facilitate financial fraud.


MITIGATION: 

	No updates are currently available to address this vulnerability.

	AusCERT advises users and sites running Internet Explorer to evaluate
	their exposure to these vulnerabilities and to apply the following
	mitigation to reduce the risk of exploitation:

	o Disable ActiveX controls in the "Internet" and "My Computer" domains,
	  as detailed below. 

	o Before visiting a trusted web site, first shut down the web browser 
	  by closing all browser windows. 

	o It is advisable not to click on any links provided in email messages.
	  If a user wishes to follow a link in an email it is best to type the
	  address into the web browser by hand.

	o Network administrators can consider blocking ActiveX controls at the
	  gateway using an application level firewall or proxy. 

	Instructions for disabling active content in Internet Explorer can be
	obtained from Microsoft's website. [2]

	The "My Computer" zone is usually not visible in the Internet Options 
	dialog. To enable it, refer to the instructions on Microsoft's 
	website. [3]


REFERENCES:

	[1] Secunia proof of concept demonstration
	    http://secunia.com/internet_explorer_cross-site_scripting_vulnerability_test/

	[2] How to Disable Active Content in Internet Explorer
	    http://support.microsoft.com/default.aspx?scid=kb;en-us;q154036

	[3] How to Enable the My Computer Security Zone in Internet Options
	    http://support.microsoft.com/?kbid=315933


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If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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