Microsoft's Security blog states the exploit could in theory be used to allow for a "remote code execution if users browse to a malicious website with an affected browser." Computerworld.com reports that the issue was first identified by the security firm Invincea and has already been used by hackers in attacks directed against the U.S. Department of Labor and U.S. Department of Energy. Microsoft is working to create a patch for IE8 that will close this exploit. 

If users don't wish to upgrade their browsers, Microsoft says some workarounds might help stop the issue. One is to set Internet and local intranet security zone settings to high, and the other is to set up IE8 to prompt users before running any Active Script type of program or to simply disable Active Scripting entirely.

Today, we released Security Advisory 2847140 regarding an issue that impacts Internet Explorer 8. Internet Explorer 6, 7, 9 and 10 are not affected by the vulnerability. This issue allows remote code execution if users browse to a malicious website with an affected browser. This would typically occur by an attacker convincing someone to click a link in an email or instant message.

Internet Explorer 9 and 10 are not affected by this issue, so upgrading to these versions will help protect you from this issue.

While we are actively working to develop a security update to address this issue, we encourage customers using affected versions of Internet Explorer to deploy the following workarounds and mitigations included in the advisory to help protect themselves:

• Set Internet and local intranet security zone settings to "High" to block ActiveX Controls and Active Scripting in these zones
  This will help prevent exploitation but may affect usability; therefore, trusted sites should be added to the Internet Explorer Trusted Sites zone to minimize disruption.
• Configure Internet Explorer to prompt before running Active Scripting or to disable Active Scripting in the Internet and local intranet security zones
  This will help prevent exploitation but can affect usability, so trusted sites should be added to the Internet Explorer Trusted Sites zone to minimize disruption.

We also always encourage people to follow the "Protect Your Computer" guidance of enabling a firewall, applying all software updates and installing anti-virus and anti-spyware software. We also encourage folks to exercise caution when visiting websites and avoid clicking suspicious links, or opening email messages from unfamiliar senders. Additional information can be found at www.microsoft.com/protect.

We are monitoring the threat landscape very closely and will continue to take appropriate action to help protect customers.

Thank you,
Dustin Childs
Group Manager, Response Communications

Microsoft confirms exploit in Internet Explorer 8