Hi, I'm proposing to stop the processing of unrequested transactions in Bitcoin Core 22.0+ at TX message reception. An unrequested transaction is one defined by which a "getdata" message for its specific identifier (either txid or wtxid) has not been previously issued by the node [0].
This change is motivated by reducing the CPU DoS surface of Bitcoin Core around mempool acceptance. Currently, an attacker can open multiple inbound connections to a node and send expensive to validate, junk transactions. Once the canonical INV/GETDATA sequence is enforced on the network, a further protection would be to deprioritize bandwidth and validation resources allocation, or even to wither connections with such DoSy peers. A permissioned peer (PF_RELAY) will still be able to bypass such restrictions. Raw TX message processing has always been tolerated by Core and as such some Bitcoin clients aren't bothering with an INV/GETDATA sequence. Such change will break their tx-relay capabilities on the p2p network and require adaptation from them. Given deployment time of any release, I hope it provides a window time wide enough before the old tx-processing behavior becomes the minority. Eager to gather feedback on this proposal, especially if such change is deemed as too much constraining or fast on any Bitcoin software. Cheers, Antoine [0] See https://github.com/bitcoin/bitcoin/pull/20277
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