"It's unclear which libraries Miele used to craft the Web server, which means without a fix from the vendor – for a dishwasher – the best option is to make sure the appliance isn't exposed to the Internet."
No. That's the second best option. The best option is not to buy anything that's given a facility to connect to the internet that it doesn't need. A dishwasher doesn't need a facility to connect to the internet.