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.

InventoryGui allows item duplication in GUIs which use GuiStorageElement