It Comes at Night (2017)
This A24 horror flick is pretty disturbing, so be warned.
Starring Joel Edgerton, Christopher Abbott, Carmen Ejogo, Kelvin Harrison Jr., and Riley Keough, it follows a family hiding out in a secluded house in the forest after the world is taken over by a horrible disease.
Their strictest rule is that they never leave the house at night — but all that is ruined when the door is found mysteriously open.