This was discovered by Richard van Eeden of Microsoft Vulnerability Research (https://lists.debian.org/debian-security-announce/2015/msg00...).
Edit: and the downvotes are because..?
http://www.zdnet.com/article/microsoft-contributes-open-sour...
MS seems to have a financial incentive in having, at least, the file sharing part of samba working. Its probably too important to ignore, and at the time, samba was how OSX talked to Windows. I imagine making Samba work was also a move to keep OSX server from becoming an enterprise competitor.
Also, I think research and netsec departments in large companies have their own priorities. Why is google finding MS vulnerabilities? I imagine a lot of this is whatever scratches the researcher's itch.
And I'm very grateful for it !