Microsoft on Monday warned of a vulnerability in its Video ActiveX Control that could allow an attacker to take control of a PC if the user visits a malicious Web site.
There have been limited attacks exploiting the hole, which affects Windows XP and Windows Server 2003, Microsoft said on its Security Response Center blog.
This is the second DirectShow security hole Microsoft has announced in the past few months. The company has yet to provide a security update for a vulnerability announced in May that involves the way DirectX handles QuickTime files.
Since there are no by-design uses for the ActiveX Control within Internet Explorer, Microsoft is recommending that users implement a workaround outlined in the security advisory. Customers can automatically implement the workaround by following the instructions under "Fix It For Me" in the Knowledge Base article for advisory number 972890 on the Microsoft support site.
Asked to explain what is meant by "no by-design uses," Christopher Budd, Security Response Communications lead, said: "In older operating systems like Windows XP that were originally developed under older programming methodologies, this ActiveX control was enabled for use within Internet Explorer by default to allow for possible future uses. These uses never materialized and as part of the more stringent security requirements that Windows Vista was developed under, this control was later disabled for use within Internet Explorer."
Even though Windows Vista and Windows Server 2008 are not affected by the vulnerability, Microsoft is recommending that users of those products also use the workaround.
Microsoft is working on a security update and will release it when the quality is at the appropriate level for broad distribution, the company said.
The Microsoft Video Control object is an ActiveX control that connects Microsoft DirectShow filters for use in capturing, recording, and playing video. The control is the main component used in Windows Media Center for building filter graphs for recording and playing television video.
When it is used in IE, the control can corrupt the system state in such a way that arbitrary code could be run by an attacker. If the user is logged in with administrative rights, the attacker could take complete control of the system.
Antivirus vendor Symantec said it was seeing the flaw being exploited in China and other parts of Asia and cited reports that indicate thousands of Web sites are hosting the exploit.
Internet Explorer versions 6 and 7 are at risk, but people running IE 8 are not vulnerable, Symantec said.
Updated July 7 8:25 a.m. PDT with Microsoft explanation of "by-design," and July 6 at 11:45 a.m. PDT with background on a previous DirectShow hole and more details on exploits of the most recent hole.