notice that Simon Pegg's name isn't listed in the cast credits of the poster. Odd. But that by itself isn't necessarily evidence that the poster is a fake. There are some movie posters here and there where the entire lead cast isn't listed so they can leave enough space to include the guest stars' names.
. It's currently on Facebook and being promoted by several fan pages. That isn't a ringing endorsement, but it's not necessarily a condemnation either. If it's phony we'll discover soon enough. Let's keep an open mind until then.