On Thursday, the software giant issued a security advisory about the potential exploit, which affects older Microsoft Office versions up through Office 2003. The current flagship Office 2007 product is not vulnerable.
Microsoft said it is only "aware of limited and targeted attacks that attempt to use this vulnerability." Users with fewer administrative rights could be less affected than those who have superuser or carte blanche access to enterprise systems, according to Redmond.
The attacks are triggered by getting users to click on a malicious Office file, either on a Web site or via an e-mail attachment, triggering malware on the user's workstation. To avoid such attacks, IT shops should have "untrusted software" policies in place, explained Paul Henry, security and forensic analyst at Lumension.
"This incident highlights the added value of application control in automatically affording protection by preventing any untrusted software," Henry said. "This [untrusted software] is software that is not explicitly permitted by policy and has been downloaded via the Internet, transferred via a USB stick or installed from a CD/DVD." The policy would prevent untrusted software from executing on a user's PC, he explained.
The PowerPoint flaw was considered "extremely critical" in a separate advisory issued on Friday by Secunia, a Denmark-based vulnerability research shop.
As a workaround, Redmond suggested that IT shops can modify the FileBlock policy in the registry to block the opening of untrusted Office 2003, and older, binary files. They can also use the Microsoft Office isolated conversion environment. This update works with Office 2003 and Office 2007 products to "more securely open Word, Excel and PowerPoint binary file formats," according to Microsoft.
Microsoft provides additional technical details on the PowerPoint vulnerability in its Microsoft Malware Protection Center and Microsoft Security Research & Defense blogs.
Microsoft plans to "continue to monitor the situation and post updates as we become aware of any important new information," according to the advisory.
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