Array index vulnerability in Microsoft Office Excel 2000 SP3, 2002 SP3, and 2003 SP3; Excel Viewer 2003 Gold and SP3; Office 2004 and 2008 for Mac; and Open XML File Format Converter for Mac allow remote attackers to execute arbitrary code via an Excel spreadsheet with a NAME record that contains an invalid index value, which triggers stack corruption, aka "Excel Global Array Memory Corruption Vulnerability."

http://www.microsoft.com/technet/security/Bulletin/MS08-074.mspx

Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266

A remote code execution vulnerability exists in Microsoft Office Excel as a result of stack corruption when loading Excel records. The vulnerability could allow remote code execution if a user opens a specially crafted Excel file that includes a malformed object. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.