fix(rpc): bound async operation queue to prevent memory DoS#465
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WalletRpcImpl stored every async RPC operation in an unbounded Vec with no automatic pruning. An authenticated caller could exhaust memory by flooding z_sendmany or z_shieldcoinbase without polling results. Prune finished operations before enqueueing new ones, reject new async RPCs when 64 in-flight operations are already queued (matching Bitcoin Core's DEFAULT_HTTP_WORKQUEUE), and check the limit before spawning the background task. Co-Authored-By: Composer <noreply@cursor.com>
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Summary
WalletRpcImpl::async_opswas an unboundedVec<AsyncOperation>with no automatic pruning.success,failed,cancelled) before enqueueing new async RPCs.DEFAULT_HTTP_WORKQUEUEused byzcashd's RPC layer.Vulnerability analysis
An authenticated JSON-RPC caller (HTTP basic auth) could call
z_sendmanyorz_shieldcoinbaserepeatedly without callingz_getoperationresult. Each call appended anAsyncOperationretaining full RPC parameters (ContextInfo.paramsasJsonValue) until explicitly removed. There was no maximum size, expiration, or background cleanup — enabling linear memory growth until OOM.