Vulnerability identifier: #VU1371

Vulnerability risk: Critical

CVSSv3.1: 8.9 [CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:F/RL:O/RC:C]

CVE-ID: CVE-2009-1134

CWE-ID: CWE-119

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Microsoft Excel
Client/Desktop applications / Office applications
Microsoft Office
Client/Desktop applications / Office applications

Vendor: Microsoft

Description
The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The weakness exists due to buffer overflow when parsing the Excel spreadsheet file format. A remote attacker can create a specially crafted Excel file containing a malformed record pointer, trick the victim into opening it, trigger memory corruption and execute arbitrary code on the target system with privileges of the current user.

Successful exploitation of the vulnerability results in arbitrary code execution on the vulnerable system.

Note: according to reports this vulnerability was being actively exploited before Microsoft issued security patch.

Mitigation
Install update from vendor's website:

Microsoft Office Excel 2007 Service Pack 1:
https://www.microsoft.com/downloads/details.aspx?familyid=2bcd565a-6acb-407d-80da-0398526ddf99
http://go.microsoft.com/fwlink/?LinkID=143568
Microsoft Office Excel 2007 Service Pack 2:
https://www.microsoft.com/downloads/details.aspx?familyid=2bcd565a-6acb-407d-80da-0398526ddf99
Microsoft Office Excel Viewer:
https://www.microsoft.com/downloads/details.aspx?familyid=ac0530dc-7f63-4ad0-85c1-784ad28156cf
http://go.microsoft.com/fwlink/?LinkID=143568
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 1 and Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 2:
https://www.microsoft.com/downloads/details.aspx?familyid=a8be8457-b0b6-455e-907e-d13be883adf2
https://www.microsoft.com/downloads/details.aspx?familyid=a8be8457-b0b6-455e-907e-d13be883adf2

Vulnerable software versions

Microsoft Excel:

Microsoft Office: 2007

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External links
http://technet.microsoft.com/en-us/library/security/ms09-021.aspx
http://fe-ddis.dk/cfcs/CFCSDocuments/Zeroday.pdf

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, a fully functional exploit for this vulnerability is available.