I suspect most whitehat researchers would be happier to report this vulnerability and make a nice legal reward, then delve into a black hat market for selling a vulnerability. Seems pretty win-win in this case.
"When we have a client that wants a zero-day vulnerability for whatever reason, we don’t ask, and in fact they wouldn’t tell us,” Mitnick tells WIRED in an interview. “Researchers find them, they sell them to us for X, we sell them to clients for Y and make the margin in between.”
http://www.wired.com/2014/09/kevin-mitnick-selling-zero-day-...
Attacking others who use the software is an entirely different story of course.