0-conf possible attack using large transactions
By making a very simple modification to the monero-wallet-rpc, one can generate a valid low priority transaction that is small enough to be relayed, but large enough to never be confirmed by the network. After looking through the code. I looked through the code and I didn't see a protection against this kind of attack.   

After 24 hours this transaction will drop from the mempool and the sender will be able to use the Monero again.