Microsoft Internet Explorer is prone to a memory-corruption vulnerability that is related to the instantiation of COM objects. This issue stems from a design error. The vulnerability arises because of the way Internet Explorer tries to instantiate certain COM objects as ActiveX controls, resulting in arbitrary code execution. The affected objects are not intended to be instantiated through Internet Explorer.
Run all software as a nonprivileged user with minimal access rights.
Ensure that all non-administrative tasks, such as browsing the web and reading email, are performed as an unprivileged user with minimal access rights.
Do not follow links provided by unknown or untrusted sources.
Users should never visit sites of questionable integrity or follow links provided by unfamiliar or untrusted sources.
Set web browser security to disable the execution of script code or active content.
Disabling scripting and active content in the Internet Zone may limit exposure to this and other vulnerabilities.
Implement multiple redundant layers of security.
As an added precaution, deploy memory-protection schemes (such as non-executable stack/heap configuration and randomly mapped memory segments). This may complicate exploitation of memory-corruption vulnerabilities.
Microsoft has released an advisory to address this and other issues in supported versions of the affected application. Some reports indicate that this issue was not properly addressed by Microsoft; third-party COM objects could still be used to exploit this issue. Symantec could not confirm this. Please see the references for more information. MS06-042 has been reissued to address a vulnerability introduced with the previous fixes. Please see BID 19667 (Microsoft Internet Explorer HTTP 1.1 and Compression Long URI Buffer Overflow Vulnerability) for further information on this issue. Microsoft Security Bulletin MS06-042 has been updated to address a flaw in Mshtml.dll that was introduced in the previous fixes. Please see the referenced advisory for more information.