Microsoft plans to issue two emergency patches next week that fix vulnerabilities in the Internet Explorer browser and Visual Studio developer suite that allow attackers to remotely execute malware.

The patches, which will be delivered on Tuesday, will be only the third time Microsoft has issued an out-of-band security patch in the past 25 months. That suggests the updates are serious enough to warrant the extra fuss. Typically, the company issues patches on the second Tuesday of each month to allow administrators time to plan for and test the updates.

In an advanced notice published late Friday, the company gave few details about the vulnerability. The patch for IE is rated "critical," the highest severity designation on Microsoft's four-notch scale. The update for Visual Studio is rated one notch lower, at "important." Both fixes will require machines to be rebooted.

"While this release is to address a single, overall issue, in order to provide the broadest protections possible to customers, we’ll be releasing two separate security bulletins," a Microsoft spokesman said in a statement.

It went on to say: "While we can’t go into specifics about the issue prior to release, we can say that the Visual Studio bulletin will address an issue that can affect certain types of applications. The Internet Explorer bulletin will provide defense-in-depth changes to Internet Explorer to help provide additional protections for the issues addressed by the Visual Studio bulletin. The Internet Explorer update will also address vulnerabilities rated as Critical that are unrelated to the Visual Studio bulletin that were privately and responsibly reported."

Earlier this week, Brian Krebs's Security Fix blog reported Microsoft intended to issue an out-of-band patch that was related to a vulnerability designated MS09-032, which Microsoft fixed 10 days ago. The report said an additional patch may be needed because the first one repaired only a subset of the vulnerable code.

Attacks targeting MS09-032 have been underway since early this month. People who have installed the patch for that vulnerability remain protected from those attacks, Microsoft's statement said.

The underlying bug was discovered by researchers Ryan Smith and Alex Wheeler and reported to Microsoft in April or May of 2008. <strke>On the same day The day after Microsoft plans to issue the emergency fix, Smith and two other researchers plan to deliver this talk at the Black Hat security conference detailing "a nuanced and precarious trust layer between" components in technologies including javascript, .NET, and browser plugins."

A preview of the talk is available here. ®