======================================================================== = Excel - Buffer Overflow In Microsoft Excel = = MS Bulletin posted: = http://www.microsoft.com/technet/security/bulletin/MS04-033.mspx = = Affected Software: = Microsoft Office 2000 Service Pack 3 Software: = - Excel 2000 = Microsoft Office XP Software: = - Excel 2002 = Microsoft Office 2001 for Mac: = - Excel 2001 for Mac = Microsoft Office v. X for Mac: = - Excel v. X for Mac = = Public disclosure on October 14, 2004 ======================================================================== == Overview == 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 value from a file/packet as a text length parameter, that is what happened here. When testing the SA-FileFoxyFuxoryFinder program, we quickly identified the existance of a SBDA in Microsoft Excel. SBDA (Same Bug, Different App) Microsoft Excel will read a value from an excel file and use this as the 'length' parameter when copying a string. By setting this to a large value, it is possible to cause a stack overflow leading to the control of EIP and other important registers. Attempted exploitation will result in an event log entry similar to; Application popup: EXCEL.EXE - Application Error : The exception Privileged instruction. (0xc0000096) occurred in the application at location 0x########. == Exploitation == Remote exploitation through Internet Explorer can be obtained through the use of an iframe or other similar object to open a file from a public UNC share or through a 'coupled' browser exploit that saves the file to a known location before opening it. Internet Explorer will automatically open the corrupt excel spreadsheet, leading to exploitation. There may of course also be other ways of having a corrupt file loaded without requiring a user to download and open it, although a excel spreadsheet may be easily accepted by a user anyway. == Solutions == - Install the vendor supplied patch. == Credit == Discovered and advised to Microsoft July 23, 2004 by Brett Moore of Security-Assessment.com %-) Da Pimp, M Burnett, Shammah, the local boys == 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. If you are not the intended recipient, you are not authorised to use or copy this message or attachment or disclose the contents to any other person. Views expressed are not necessarily endorsed by Security-Assessment.com Limited. Please note that this communication does not designate an information system for the purposes of the New Zealand Electronic Transactions Act 2003. ######################################################################