JustEnoughItems (JEI) 19.5.0.33 and before contains an Improper Validation of Specified Index, Position, or Offset in Input vulnerability. The specific issue is a failure to validate slot index in JEI for Minecraft, which allows in-game item duplication.
https://github.com/mezz/JustEnoughItems/commit/99ff43ba1009c44c6d935e2ab8a6c9292bb12873
https://gist.github.com/apple502j/05123abb1d1c89c31afde15a9b34e2ae