loose lip(s)
The practice, habit, or manner of speaking too frequently and/or without discretion, especially as might unintentionally lead to revealing private or sensitive information to others. You've got a very loose lip, son. You'd do well to learn to keep it shut! The details of this project are extremely confidential, so make sure you don't have loose lips about it.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.