Software Engineering Institute

Microsoft Excel contains a vulnerability that could be exploited when Excel opens a specially crafted document. It is possible that the vulnerability can be exploited by opening a Microsoft Office document that includes an embedded Excel spreadsheet. Based on limited testing, Excel 2003, Excel Viewer 2003, Excel XP (2002), Excel 2000, Excel 97, Excel Viewer 97, and Excel 2004 for Mac OS appear to contain a buffer overflow vulnerability. Other versions of Excel may also be affected. Microsoft Security Advisory (921365) indicates that the vulnerability is related to Excel's repair mode.

By convincing a user to open a specially crafted Excel document, an attacker could execute arbitrary code with the privileges of the user running Excel. If the user is logged in with administrative privileges, the attacker could take complete control of a vulnerable system.

Apply an update

This vulnerability is addressed in Microsoft Security Bulletin MS06-037.

Do not open untrusted Excel documents

Do not open unfamiliar or unexpected Excel or other Office documents, particularly those hosted on web sites or delivered as email attachments. Please see Cyber Security Tip ST04-010.

Do not rely on file name extension filtering

In most cases, Windows will call Excel to open a document even if the document has an unknown file extension. For example, if spreadsheet.qwer contains the correct file header information, Windows will open spreadsheet.qwer with Excel. Filtering for common extensions (e.g., .xls, .xlt, .csv) will not detect all Excel documents.