MBSA 2.3 Preview has been released on the Client Management Connect site to the ConfigMgr Open Beta community.
MBSA 2.3 release adds support for Windows 8, Windows 8.1, Windows Server 2012, and Windows Server 2012 R2. Windows 2000 will no longer be supported with this release. The final release of MBSA 2.3 is expected to be available in Fall 2013.
You can download MBSA 2.3 Preview here.