Exploitable inventory component chaining in PocketMine-MP

Summary

### Impact Specially crafted `InventoryTransactionPacket`s sent by malicious clients were able to exploit the behaviour of `InventoryTransaction->findResultItem()` and cause it to take an abnormally long time to execute (causing an apparent server freeze). The affected code is intended to compact conflicting `InventoryActions` which are in the same `InventoryTransaction` by flattening them into a single action. When multiple pathways to a result existed, the complexity of this flattening became exponential. The problem was fixed by bailing when ambiguities are detected. **At the time of writing, this exploit is being used in the wild by attackers to deny service to servers.** ### Patches Upgrade to 3.15.4 or newer. ### Workarounds No practical workarounds are possible, short of backporting the fix or implementing checks in a plugin listening to `DataPacketReceiveEvent`. ### References c368ebb5e74632bc622534b37cd1447b97281e20 ### For more information If you have any questions or comments about this advisory: * Email us at [[email protected]](mailto:[email protected])