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Buffer Overflow In Microsoft Excel
From: "Brett Moore" <brett.moore () security-assessment com>
Date: Thu, 14 Oct 2004 11:00:44 +1300

========================================================================
= Excel - Buffer Overflow In Microsoft Excel
=
= MS Bulletin posted: 
= http://www.microsoft.com/technet/security/bulletin/MS04-033.mspx
=
= Affected Software:
=       Microsoft Office 2000 Service Pack 3 Software:
=       - Excel 2000
=       Microsoft Office XP Software:
=       - Excel 2002
=       Microsoft Office 2001 for Mac:
=       - Excel 2001 for Mac
=       Microsoft Office v. X for Mac:
=       - Excel v. X for Mac
=
= Public disclosure on October 14, 2004
========================================================================

== Overview ==

When thinking about buffer overflow vulnerabilities, a file can sometimes
be as harmful as a packet. Even though past security issues have taught
us that it is unwise to use an unvalidated value from a file/packet as 
a text length parameter, that is what happened here.

When testing the SA-FileFoxyFuxoryFinder program, we quickly identified
the existance of a SBDA in Microsoft Excel. SBDA (Same Bug, Different App)

Microsoft Excel will read a value from an excel file and use this as the
'length' parameter when copying a string. By setting this to a large
value, it is possible to cause a stack overflow leading to the control
of EIP and other important registers.

Attempted exploitation will result in an event log entry similar to;
  Application popup: 
  EXCEL.EXE - Application Error : The exception Privileged instruction.
  (0xc0000096) occurred in the application at location 0x########.

== Exploitation ==

Remote exploitation through Internet Explorer can be obtained through the
use of an iframe or other similar object to open a file from a public
UNC share or through a 'coupled' browser exploit that saves the file to
a known location before opening it. Internet Explorer will automatically
open the corrupt excel spreadsheet, leading to exploitation.

There may of course also be other ways of having a corrupt file loaded
without requiring a user to download and open it, although a excel 
spreadsheet may be easily accepted by a user anyway.

== Solutions ==

- Install the vendor supplied patch.

== Credit ==

Discovered and advised to Microsoft July 23, 2004 by Brett Moore of
Security-Assessment.com

%-) Da Pimp, M Burnett, Shammah, the local boys

== About Security-Assessment.com ==

Security-Assessment.com is a leader in intrusion testing and security
code review, and leads the world with SA-ISO, online ISO17799 compliance
management solution. Security-Assessment.com is committed to security
research and development, and its team have previously identified a
number of vulnerabilities in public and private software vendors products.

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