Software Engineering Institute

Microsoft Excel contains a vulnerability. According to Microsoft Security Bulletin MS07-015

The vulnerability is caused when Excel opens a specially crafted Excel file which will results in the access of memory outside intended regions when parsing placeholder data.

This vulnerability affects Microsoft Excel for both Microsoft Windows and Mac OS X.

By convincing a user to open a specially crafted Office document, an attacker could execute arbitrary code.

Apply Update for Microsoft
Microsoft has addressed this vulnerability in Microsoft Security Bulletin MS07-015.

Do not open untrusted Office 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 the appropriate Office application to open a document even if the document has an unknown file extension. For example, if document.qwer contains the correct file header information for a Excel document, Windows will open document.qwer with Excel. Filtering for common Office file extensions (e.g., .xls, .doc, and .ppt) will not detect all Office documents.

Disable automatic opening of Microsoft Office documents

By default, Microsoft Office 97 and Microsoft Office 2000 will configure Internet Explorer to automatically open Microsoft Office documents. This feature can be disabled by using the Office Document Open Confirmation Tool. Mozilla Firefox users should disable automatic opening of files, as specified in the Securing Your Web Browser document.