How dangerous is running an old DS212j?

I looked over the last few posts and saw a few of the same questions except my situation is a little different. I did not buy this unit, I got it from an old job and played around with it for a few years until the OS no longer got updates so I shut it down (DSM 6 I think?). Now I'm thinking of trying to use it again but only for drive storage/file sharing. I won't be using it for anything else other than that. Is there any security risk from running it with the old OS if there's no external access?