Microsoft on Monday issued a security advisory about a zero-day vulnerability in the Microsoft Video ActiveX Control. The flaw could allow a remote unauthenticated attacker to execute malicious code on computers running Windows XP and Windows 2003 Server.

"A browse-and-get-owned attack vector exists," acknowledged Microsoft security engineer Chengyun Chu on the company's Security Research & Defense blog. "A user needs to be lured to navigate to a malicious Web site or a compromised legitimate Web site to be affected. No further user interaction is needed."

And legitimate Web sites may be compromised merely by hosting content submitted by users. Such content or advertisements could be crafted to exploit the Video ActiveX Control vulnerability.

Chu notes that Outlook Express and Outlook will open HTML e-mail messages in the Restricted sites zone by default. This prevents ActiveX controls from being used when reading those messages. However, clicking on a link in such a message could still initiate a browser-based attack.

The specific vulnerable file is Microsoft's MPEG2TuneRequest ActiveX Control Object. The company recommends setting the kill-bit on this ActiveX object as a workaround until a patch is released.

Microsoft provides a link on its Security Research & Defense blog that will disable the vulnerable ActiveX control.

In February, Microsoft issued a security advisory about a zero-day Excel 2007 vulnerability. It issued a fix for the flaw during its April patch cycle.

In June, Microsoft issued set of software patches that addressed 31 vulnerabilities in 10 separate security bulletins, the largest number of vulnerabilities fixed in a single day since the company began issuing regular patches on the second Tuesday of every month in October 2003.

Microsoft plans to release its July patches next Tuesday. It's unlikely the company will have had enough time to prepare a patch for the Video ActiveX control vulnerability.