Multiple vulnerabilities have been reported in Microsoft Office Excel, which can be exploited by malicious people to compromise a user's system.

1) An integer underflow error when parsing data included in a 400h substream can be exploited to cause a stack-based buffer overflow.

2) A signedness error when parsing record data from external XLS files can be exploited to cause a buffer overflow via an external XLS file defining an overly large record size.

3) An error when processing variable-sized content in RealTimeData records can be exploited to corrupt memory when copying data from file.

4) An unspecified error when parsing certain records can be exploited to corrupt memory.

5) An error when parsing certain records can be exploited to cause a buffer overflow.

6) Improper initialisation of a variable used as the "count" argument for a call to memcpy() when parsing certain content can be exploited to cause a buffer overflow.

Successful exploitation of the vulnerabilities allows execution of arbitrary code.

Solution
Apply patches.
Further details available to Secunia VIM customers

Provided and/or discovered by
1, 2) Alin Rad Pop, Secunia Research.
4) An anonymous person via iDefense.
3, 6) Aniway via ZDI.

The vendor credits:
3) Muhammad Junaid Bohio, Telus Security Labs.
5) Rodrigo Rubira Branco, Check Point Vulnerability Discovery Team.

Changelog
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Original Advisory
MS11-021 (KB2464583, KB2466146, KB2466156, KB2466158, KB2466169, KB2489279, KB2502786, KB2505924, KB2505927, KB2505935, KB2525412):
http://www.microsoft.com/technet/security/Bulletin/MS11-021.mspx

Secunia Research:
http://secunia.com/secunia_research/2011-31/
http://secunia.com/secunia_research/2011-32/

iDefense:
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=901

ZDI:
http://www.zerodayinitiative.com/advisories/ZDI-11-120/
http://www.zerodayinitiative.com/advisories/ZDI-11-121/

Technical Analysis
Further details available to Secunia VIM customers

Deep Links
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