Someone tapped into romex ( which supplies power to living space wall
outlet) to power a light fixture (bare bulb, grounded outlet and box)
in crawl space. This is exposed romex running under floor joists.
At the connection there are wire nuts but this is not contained in a
junction box. Should it be? Is it a safety issue?

I would put one there anyway just for neatness, but romex has very
little slack and I doubt that I could get it into a junction box
without making another connection, with more romex (which I do already
have) and yet another junction box..
Thanks..
Chuck