InventoryGui is a library for creating chest GUIs for Bukkit/Spigot plugins. Versions before 1.6.5 contain a vulnerability where any plugin using a GUI with the GuiStorageElement and allows taking out items out of that element can allow item duplication when the experimental Bundle item feature is enabled on the server. The vulnerability is resolved in version 1.6.5.
The product requires that an actor should only be able to perform an action once, or to have only one unique action, but the product does not enforce or improperly enforces this restriction.