Microsoft Office Excel Remote Memory Corruption Vulnerability

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Microsoft Office Excel Remote Memory Corruption Vulnerability
2009.April.14

Fortinet's FortiGuard Global Security Research Team Discovers Vulnerability in Microsoft Office Excel.

Summary:
========
A memory corruption vulnerability exists in Microsoft Office Excel which allows a remote attacker to compromise a 
system through a malicious document.

Impact:
=======
Remote Code Execution.

Risk:
=====
Critical

Affected Software:
==================
For a list of operating system and product versions affected, please see the Microsoft Bulletin reference below.

Additional Information:
=======================
The vulnerability lies in "excel.exe", which is used when processing an Excel file. A maliciously crafted document will 
cause Excel to crash when processing. The crash occurs while calculating memory using an offset and a two-byte value 
contained in the document. If the two-byte value is set to a high value, an overflow condition will occur during memory 
calculation. A remote attacker can potentially control the memory referenced as a result of the overflow to alter 
program flow, and execute arbitrary code on a victims machine.

Solutions:
==========
Use the solution provided by Microsoft (MS09-009). 
The FortiGuard Global Security Research Team released a signature "MS.Excel.OBJ.Subrecord.Code.Execution", which covers 
this specific vulnerability.

Fortinet customers who subscribe to Fortinet's intrusion prevention (IPS) service should be protected against this 
memory corruption vulnerability. Fortinet's IPS service is one component of FortiGuard Subscription Services, which 
also offer comprehensive solutions such as antivirus, Web content filtering and antispam capabilities. These services 
enable protection against threats on both application and network layers. FortiGuard Services are continuously updated 
by the FortiGuard Global Security Research Team, which enables Fortinet to deliver a combination of multi-layered 
security intelligence and true zero-day protection from new and emerging threats. These updates are delivered to all 
FortiGate, FortiMail and FortiClient products. Fortinet strictly follows responsible disclosure guidelines to ensure 
optimum protection during a threat's lifecycle.

References:
===========
FortiGuard Advisory: http://www.fortiguardcenter.com/advisory/FGA-2009-16.html
Microsoft Bulletin: http://www.microsoft.com/technet/security/Bulletin/ms09-009.mspx
CVE ID: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-0100

Acknowledgement:
================
Haifei Li of Fortinet's FortiGuard Global Security Research Team


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