Original title (KR): 검은 수녀들 (Geom-eun sunyeodeul, The Black Nuns)

Desperation drives Sister Yunia (Song Hye-kyo) to perform an exorcism no nun should attempt. With a possessed child at the mercy of evil, she teams up with Sister Michaela (Jeon Yeo-been), a reluctant apprentice, to enact a forbidden ritual. Breaking the sacred rule of their order, they must confront the terrifying cost of their sacrilegious actions, but one goal remains: the boy must be saved at all costs.

www.themoviedb.org/movie/1224993