In MS02-022 the only workaround Microsoft lists is this: "Do not open or save .job files that you receive from untrusted sources." As you mentioned, this vulnerability can be triggered automatically without user interaction and without opening or saving .job files by navigating to an explorer folder that contains a malicious .job file, which can be done either locally, remotely on a webpage or inside an HTML email. The primary cause of this automated exploitation is the concept of dynamic icon handlers. For an introduction to these, read the "Creating Icon Handlers" article at http://msdn.microsoft.com/library/en-us/shellcc/platform/shell/programme rsguide/shell_int/shell_int_extending/extensionhandlers/iconhandlers.asp (short: http://tinyurl.com/3uanu ) To quote: "An icon handler is a type of Shell extension handler that allows you to dynamically assign icons to the members of a file class. Every time a file from the class is displayed, the Shell queries the handler for the appropriate icon. For instance, an icon handler can assign different icons to different members of the class, or vary the icon based on the current state of the file." To summarize, every time you open a directory in an Explorer window, Explorer will examine each and every filetype in that directory and determine whether each filetype has an associated icon handler. When you look at .job files you get a reference to the JobObject entry in HKLM\Software\Classes\JobObject which in turn has a shellex\IconHandler entry that points at {DD2110F0-9EEF-11cf-8D8E-00AA0060F5BF} whose InProcServer32 is mstask.dll that is automatically launched without user interaction. You can completely mitigate against automated exploitation of this vulnerability simply by deleting or renaming the following registry entry: HKEY_LOCAL_MACHINE\SOFTWARE\Classes\JobObject\shellex\IconHandler The only noticable difference is that your .job files will not have as pretty of an icon. I'm positive that following your advisory we will find other vulnerabilities involving dynamic icon handlers. It's quite easy to mitigate against this potential impact simply by removing all dynamic icon handlers and I'll be testing the cosmetic impact of this in the days to come. Removing the automated attack vector means that the only way to have this exploited is to convince the user to launch Task Scheduler and import your malicious .job file. As Brett mentions, Qwik-Fix Pro protects against automated remote exploitation of this vulnerability and you can get a free copy at http://qwik-fix.net/. Microsoft should update the MS02-022 bulletin to reflect that automated exploitation is possible. Currently, the only listed affected software is Windows 2000 but I had no problems reproducing this on Windows XP as well. Since there is no patch available for Windows XP to fix this vulnerability the only workaround is to disable the dynamic icon handler for JobObject files, as described above. Regards Thor Larholm Senior Security Researcher PivX Solutions 23 Corporate Plaza #280 Newport Beach, CA 92660 http://www.pivx.com thor@xxxxxxxx Stock symbol: (PIVX.OB) Phone: +1 (949) 231-8496 PGP: 0x4207AEE9 B5AB D1A4 D4FD 5731 89D6 20CD 5BDB 3D99 4207 AEE9 PivX defines a new genre in Desktop Security: Proactive Threat Mitigation. <http://www.pivx.com/qwikfix> -----Original Message----- From: Brett Moore [mailto:brett.moore@xxxxxxxxxxxxxxxxxxxxxxx] Sent: Tuesday, July 13, 2004 10:51 PM To: Bugtraq@Securityfocus. Com Subject: Unchecked buffer in mstask.dll ======================================================================== = Unchecked buffer in mstask.dll = = MS Bulletin posted: = http://www.microsoft.com/technet/security/bulletin/MS04-022.mspx = = Affected Software: = Microsoft Windows 2000 Service Pack 4 = Microsoft Windows XP, Microsoft Windows XP Service Pack 1 = = Public disclosure on July 14, 2004 ======================================================================== When thinking about buffer overflow vulnerabilities, a file can sometimes be as harmful as a packet. Even though past security issues have taught us that it is unwise to use an unvalidated text string containing a file name or directory, that is what happened here. By creating a .job file with a large "to be executed" field the stack can be overwritten allowing for remote command execution, when the file is parsed by mstask.dll. == Description == It appears that both explorer.exe and iexplore.exe will parse a .job file when showing folder listings. Upon the parsing of the .job file, the large "to be executed" field is passed to wcscpy without doing any bounds checking. Using explorer the viewing of a folder containing the .job is enough to cause the buffer overflow to occur. The file can be hosted locally or on a remote network share. A remote attack would require the end user to visit the folder/share containing the exploit file. Using Internet Explorer the viewing of a folder containing the .job file through the use of an [iframe] object will cause the buffer overflow to occur. Viewing an HTML email that is based around the [iframe] attack avenue, will also cause the buffer overflow. This will occur without any user intervention if the preview pane is enabled, or with user intervention by viewing the email. It is possible that there are other avenues of attack to exploit this vulnerability. == Exploitation == Remote exploitation through Internet Explorer can be obtained through the use of an iframe object pointing at an anonymous share. Automatic exploitation of browser based bugs, does not rely on an attacker sending a link, requiring the target user to click on it. Links, references and other objects can easily be opened through script code. And I am told that this can also be achieved without script code. == Solutions == - Install the vendor supplied patch. - Use browser protection products such as Qwik-Fix from PivX. They are to implement some protective measure against this very soon. == Credit == Discovered and advised to Microsoft July 7th, 2003 by Brett Moore of Security-Assessment.com %-) Thor and the PivX guys, the #unconventional and the #conversational == About Security-Assessment.com == Security-Assessment.com is a leader in intrusion testing and security code review, and leads the world with SA-ISO, online ISO17799 compliance management solution. Security-Assessment.com is committed to security research and development, and its team have previously identified a number of vulnerabilities in public and private software vendors products. ###################################################################### CONFIDENTIALITY NOTICE: This message and any attachment(s) are confidential and proprietary. They may also be privileged or otherwise protected from disclosure. If you are not the intended recipient, advise the sender and delete this message and any attachment from your system. 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