Microsoft has detailed a method users of Internet Explorer can use to secure their computers from the recently discovered exploit allowing malicious code to run on a PC.
Microsoft has admitted to the bug, which it says hurts Internet Explorer versions 6 through 9, but leaves IE 10 alone. The flaw is described as follows:
A remote code execution vulnerability exists in the way that Internet Explorer accesses an object that has been deleted or has not been properly allocated. The vulnerability may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer. An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.
Redmond's remedy is detailed in Security Advisory 2757760, which it says will there's no outright fix for the issue at present, but that users can work around the threat by deploying the Enhanced Mitigation Experience Toolkit (EMET), described as "... a utility that helps prevent vulnerabilities in software from successfully being exploited by applying in-box mitigations such as DEP to applications configured in EMET."
An EMET-ic of this nature will not be pleasant, as Redmond says the tool is offered in English alone and enjoys only limited support.
The cure may also induce other worries, as the workaround instructions suggest that applying EMET to IE will result in the browser issuing lots of security prompts to users.
"You will be prompted frequently when you enable this workaround," MIcrosoft warns. "For each prompt, if you feel you trust the site that you are visiting, click Yes to run Active Scripting. If you do not want to be prompted for all these sites, use the steps outlined in "Add sites that you trust to the Internet Explorer Trusted sites zone".
Redmond also recommends the following actions:
- 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.
Microsoft says a formal fix is in the works and "... may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs." ®