http://www.techradar.com/news/researchers-are-claiming-a-cheap-mask-can-fool-iphone-x-face-id

One of the advantages of Face ID on the iPhone X is that – according to Apple at least – it’s very, very hard to fool, and the Cupertino brand says it’s worked to stop masks fooling it.

But despite that, it seems a mask that can trick the iPhone X may already have been created.