can of worms

noun

1. Informal.,  a source of many unpredictable or unexpected problems.

   Buying a company we know nothing about would be opening up a whole new can of worms.

Word History and Origins

Origin of can of worms¹

First recorded in 1965–70

Idioms and Phrases

A complex unexpected problem or unsolvable dilemma, as in Tackling the budget cuts is sure to open a can of worms. This expression alludes to a container of bait used for fishing, which when opened reveals an inextricable tangle of worms. [1920s]