Mythological source of misfortune (8,3)
I believe the answer is:
pandoras box
(Other definitions for pandoras box that I've seen before include "In Greek mythology, what the first woman was forbidden to open" , "It was disastrous, for openers" , "Something that it's unwise to open?" , "legendary source of trouble" , "Mythical container of all the evils of the world" .)