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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