Roughly Enough Items (REI) <16.0.729 - Improper Validation
Roughly Enough Items (REI) v.16.0.729 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 and decrement stack count in the Roughly Enough Items (REI) mod for Minecraft, which allows in-game item duplication.