An issue was discovered in certain Apple products. macOS before 10.13 Supplemental Update is affected. The issue involves the "StorageKit" component. It allows attackers to discover passwords for APFS encrypted volumes by reading Disk Utility hints, because the stored hint value was accidentally set to the password itself, not the entered hint value.
https://www.theregister.co.uk/2017/10/05/apple_patches_password_hint_bug_that_revealed_password/
https://support.apple.com/HT208165
https://nakedsecurity.sophos.com/2017/10/05/urgent-update-your-mac-again-right-now/