Is there a plugin/app that allows auto banning for swearing on forum?
I wouldn't advice using something like that.
Do you know that the first song Faith No More played after a very long break is titled Motherfucker? Would you like to auto-ban users talking about something like that?
That said, there is the CivilTongueEx plugin which you could "enhance" to also punish users who have used a "bad" word.