MSO.DLL in Microsoft Office 2000, Office XP (2002), and Office 2003 allows user-assisted attackers to cause a denial of service and execute arbitrary code via multiple attack vectors, as originally demonstrated using a crafted document record with a malformed string, as demonstrated by replacing a certain "01 00 00 00" byte sequence with an "FF FF FF FF" byte sequence, possibly causing an invalid array index, in (1) an Excel .xls document, which triggers an access violation in ole32.dll; (2) an Excel .xlw document, which triggers an access violation in excel.exe; (3) a Word document, which triggers an access violation in mso.dll in winword.exe; and (4) a PowerPoint document, which triggers an access violation in powerpnt.txt. NOTE: after the initial disclosure, this issue was demonstrated by triggering an integer overflow using an inconsistent size for a Unicode "Sheet Name" string.