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Georgi Guninski security advisory #50, 2001

Javascript in IE may spoof the whole screen

Systems affected:
IE 5.5/6.0 on Windows, probably earlier versions

Risk: very low (user interaction required)
Date: 21 October 2001

Disclaimer:
The information in this advisory is believed to be true based on
experiments though it may be false.
The opinions expressed in this advisory and program are my own and
not of any company. The usual standard disclaimer applies,
especially the fact that Georgi Guninski is not liable for any damages
caused by direct or indirect use of the information or functionality
provided by this advisory or program. Georgi Guninski bears no
responsibility for content or misuse of this advisory or program or
any derivatives thereof.

Description:

This is *not* security vulnerability by itself but has some
security implications.
It is possible a web page containing javascript to take over the
whole screen - including menus, modal dialogs, taskbar, clock, etc.
This allows "spoofing" the whole screen including modal IE messages.
Basically this means that a script initiated IE dialog
"You are downloading malicous.exe from malicous.com - 'Open | Cancel |more info'"
may be made to appear to the user:
"Welcome to my new site - 'Open'" ('Cancel' is not visible and not clickable)
If the user clicks on 'Open' in the spoofed context code may be executed
(user interaction is required).

Details:
Spoofing the UI is done by window.createPopup() and popup.show() -
-------------------
op=window.createPopup();
op.document.body.innerHTML="...html...";
op.show(0,0,screen.width,screen.height,document.body);
-------------------
Demonstration:

Image moving over download/open dialog:
http://www.guninski.com/opf2.html
BSOD emulation:
http://www.guninski.com/bsod1.html

Workaround:
If you consider this threat disable "active scripting"

Vendor status:
Microsoft was informed on 16 October 2001.

Regards,
Georgi Guninski
http://www.guninski.com
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