`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: 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 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: ------------------------------------------------------------------ ------------------------------------------------------------------ In the imported file (fav.imp), residing on a samba or Windows server without authentication: -------------------------------------------------------------------

123456
123455

------------------------------------------------------------------- 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 `

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