If someone posts a POC of a crash in a piece of software but not the exploit to exploit it, and you make the exploit does it count as your find or his?
I'd think it'd be his. You would be developing an exploit using his intellectual property, the POC.
Even though there is probably nothing set in stone you'd be responsible for the code but the concept is his. On the other side of the coin it depends how detailed his POC was and how closely your exploit/code follows it, if you see what I mean.