What modern idiom describes a source of problems released by revealing a hidden issue, like Pandora's container?

“Opening Pandora’s box” is the modern idiom for releasing many problems by revealing a hidden issue.

The expression comes from the myth in which Pandora opens a sealed container and the troubles inside escape into the world. In contemporary English, the phrase usually describes an action that creates complications that are difficult or impossible to reverse.

The idiom is often used in journalism, politics, law, science, and everyday conversation. It can refer to uncovering a disputed fact, starting a risky process, or changing a system in ways that produce unexpected consequences.

Although the phrase says “box,” Hesiod’s original container was a pithos, or large jar. The box wording became established through later translation, but the idiom is now conventional English and does not require speakers to know the translation history.