"... someone hacks into your oven, turns the gas on, waits 36 hours, then lights the pilot, ..."
A sensibly design IoT oven would not allow independent control of those items from outside. It would have 'on', 'off' and 'temperature demand' inputs. Local hardware/firmware would determine any safety related activity and sequences. If it was very clever it would notice any 'crazy' external command behaviour and disconnect itself from the internet.