GHSA-65jj-fmw8-468q: zebrad has unbounded memory leak in mempool download pipeline via timeout path cancel_handles retention

Am I affected You are affected if: 1. You run zebrad up to and including v4.4.1. 2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default). 3. Your node's mempool is active (node is synced near the chain tip). All default configurations are affected. Summary The mempool download pipeline's cancel_handles map retains entries for transactions whose verification times out at the outer RATE_LIMIT_DELAY (73-second) boundary. The tokio::time::error::Elapsed error carries no payload, so the transaction ID is unrecoverable and the corresponding cancel_handles entry (including the full Gossip::Tx(UnminedTx), up to ~2 MB) is never removed. Entries accumulate monotonically with no upper bound or garbage collection, leading to eventual out-of-memory process termination. Details Downloads::poll_next() at zebrad/src/components/mempool/downloads.rs:215-228 handles three terminal states for a verification task: - Ok(Ok(...)): success. Calls cancel_handles.remove(&tx.transaction.id). Correct. - Ok(Err(...)): verification error. Calls cancel_handles.remove(&hash). Correct. - Err(elapsed): outer timeout. Returns Err(elapsed) without removing anything. Bug. tokio::time::error::Elapsed has no payload, so the timed-out transaction's UnminedTxId is unrecoverable from the error. The consumer at zebrad/src/components/mempool.rs:663-672 explicitly acknowledges this gap with a TODO comment. The only cleanup paths for cancel_handles are cancel(mined_ids) (removes entries matching mined transaction IDs; attacker transactions are never mined) and cancel_all() (clears everything on shutdown or chain reset). No periodic GC, no time-based eviction, and no count cap exists. For direct tx pushes (Gossip::Tx), the retained entry holds the full deserialized transaction, which can be up to ~9 MB in memory for a transaction near the transparent-output extreme. Per-connection leak rate at worst