This Tuesday Microsoft released its first security bulletin for Hyper-V.
The vulnerability, which could lead to a Denial of Service (DoS), consists in a malformed sequence of instructions that a locally authenticated user has execute on a guest operating system.
It applies to all versions of Hyper-V, including Windows Server Hyper-V (2008, 2008 R2 and Server Core editions) and the stand-alone Hyper-V Server (2008, 2008 SP2 and 2008 R2 editions).
The vulnerability doesn’t affect the guest operating systems, it cannot be remotely exploited, it cannot be exploited by anonymous users inside the guest OS and it can’t be used for privileges escalation inside the hypervisor layer.
Additional information about affected files available here.