Don't know if its an exploit or not.

For it to be an exploit, you have to make the site do something that is not intended, I’d say. At best it is an indication of a possible vulnerability, but this doesn’t sound like something that is accidental.

Are you sure this is exactly what you did? I could see it as a feature to help users, but it seems a bit far-fetched.

Yeah I have tried it multiple times since and it always works, have no idea why in all honesty dude. Thought you guy’s might find it interesting none the less.

I wonder why it would do that then?

Just in case you are not trolling, I tried it and I cannot reproduce. (And it doesn’t let me set an empty password, which would make it work trivially.)

Perhaps you are not logging in via a browser but an app? Or are you being hacked? ;)

After I tried it and tried logging in normally, it suddenly said it was down for maintenance. Perhaps you hacked me? oO

I reported it to facebook bro, maybe they fixed the gap? Rightly or wrongly I told facebook about it after posting this. Highly unlikely I could hack you dude, I can’t even get burpsuite to work properly lol. Highly likely I have been hacked though lol.