Microsoft on Thursday issued a security advisory concerning a zero-day vulnerability in Microsoft Office PowerPoint.

If a user can be convinced to open a maliciously crafted PowerPoint file -- contained in an e-mail message or via a Web site link -- the vulnerability could allow an attacker to execute code remotely.

"Usually, these files look legit when opened so it is quite easy to fall prey and not even notice that something malicious ran in the background," explain Microsoft security engineer Cristian Craioveanu and program manager Ziv Mador in a blog post.

Affected versions of Microsoft Office PowerPoint for Windows include 2000 SP3, 2002 SP3, and 2003 SP3, as well as Microsoft Office 2004 for Mac. Office 2007, the most recent Office suite, is not affected.

Microsoft said that it's aware only of limited, targeted attempts to exploit this vulnerability.

In another blog post, Microsoft Security Response Center engineers Bruce Dang and Jonathan Ness offer further information about the problem.

"The malware samples we have seen exploiting this vulnerability are the first reliable exploits we have seen in the wild that infect Office 2003 SP3 with the latest security updates," they state. "Office 2003 SP3 (released Sept 2007) had a good run being safe from the bad guys but we missed this bug while back-porting fixes found in the Office 12 fuzzing effort to Office 2003 SP3. SP3 was a massive security push that we recommend all Office 2003 customers apply (this vulnerability notwithstanding)."

Fuzzing is a software testing method that involves supplying an application with random data in an effort to make it crash or show other effects.

Dang and Ness explain that PowerPoint files in the latest XML file format are not affected. Organizations that have migrated to PPTX, PowerPoint's XML format, can disable the affected binary file format through the FileBlock registry settings provided in the security advisory.

Another alternative is to force older PowerPoint files to open in MOICE, the Microsoft Isolated Conversion Environment, a security feature that converts various Microsoft Office binary file formats into Office Open XML format.

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