The specific flaw exists within the handling of registry links. An attacker running code in a low-integrity Internet Explorer process can set a registry link that will be followed by the medium-integrity broker process, which will then reduce the security of the target registry key in such a way that it can be modified by low-integrity Internet Explorer processes. These registry keys can be used to execute medium-integrity processes from low-integrity Internet Explorer processes.
Microsoft has issued an update to correct this vulnerability. More details can be found at:
|Ashutosh Mehra (https://twitter.com/ashutoshmehra)