Today we released Security Advisory 2887505 regarding an issue that affects Internet Explorer. There are only reports of a limited number of targeted attacks specifically directed at Internet Explorer 8 and 9, although the issue could potentially affect all supported versions. This issue could allow remote code execution if an affected system browses to a website containing malicious content directed towards the specific browser type. This would typically occur when an attacker compromises the security of trusted websites regularly frequented, or convinces someone to click on a link in an email or instant message. Running modern versions of Internet Explorer ensures that customers receive the benefit of additional security features that can help prevent successful attacks.

While we are actively working to develop a security update to address this issue, we encourage Internet Explorer customers concerned with the risk associated with this vulnerability, to deploy the following workarounds and mitigations from the advisory:

  • Apply the Microsoft Fix it solution, "CVE-2013-3893 MSHTML Shim Workaround," that prevents exploitation of this issue
    See Microsoft Knowledge Base Article 2887505 to use the automated Microsoft Fix it solution to enable or disable this workaround.
  • 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.

As a best practice, we always encourage customers 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 customers 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 our customers.

Thank you,

Dustin Childs
Group Manager, Response Communications
Trustworthy Computing