oak_techniques: [OAK-T10.002.001] spec_id: oak-detection-T10.002.001 version: 0.1.0 maturity: emerging maintainer: "@iZonex" license: Apache-2.0 scope: | Detect bridge / intents incidents where the failing verification predicate sits in an OFF-CHAIN observer (relayer, filler, solver, indexer, executor) that decides a source-chain event occurred and causes destination-side value release. The on-chain contracts are correct and do exactly what they are instructed; the instruction is wrong. Two sub-shapes: (a) PARSE-LEVEL — the observer reconstructs an event from raw chain data without asserting the record's type identity (Across 2026-07: unchecked 8-byte Anchor discriminator on Solana, where events are rebuilt from traces and failed transactions still emit data); (b) SEMANTIC / CUSTODY-LEVEL — the observer validates a well-formed message's fields but never the fact the message asserts (Coreum-XRPL 2026-08: memo amount and recipient checked, actual XRP receipt never checked). Excludes: T10.002 parent (failing predicate in deployed bytecode); T10.001 (validator-key compromise — in both anchors the signers were honest and the authorisation genuine); T10.003 (replay of a legitimate message); T11.011 (observer's own hot keys stolen, e.g. LayerZero Executor 2026-07 — the observer was the victim, not the deceived party). data_sources: [bridge_deposit_log, bridge_lock_release_events, bridge_message_logs, tx_call_trace, contract_events, onchain_transaction, simulation_environment] detection_logic: description: | Four orthogonal paths, ordered by prevention value. PATH A (locked-vs-issued gate) is the prevention-grade control and belongs INSIDE the operator's release path, not in a periodic report: before releasing X, confirm custody state actually rose by X. PATH B (type-identity assertion) closes the parse-level shape at the point of parsing. PATH C (source-transaction sanity) catches fills keyed to transactions that moved nothing or failed. PATH D (reserve-depletion velocity) is the runtime backstop that bounds any verification failure the first three miss, and is the only path that fires without instrumenting the observer itself. pseudocode: | # PATH A — locked-versus-issued gate in the release path on observer_release_decision(claim): # claim = {asset, amount, src_ref} custody_now ← custody_balance(bridge_custody_account, claim.asset) custody_mark ← last_reconciled_balance(bridge_custody_account, claim.asset) credited ← Σ released(claim.asset, since = last_reconciliation) if custody_now − custody_mark < credited + claim.amount − reconcile_tolerance: emit(PATH_A, bridge=claim.bridge, asset=claim.asset, claimed=claim.amount, custody_delta=custody_now−custody_mark, mode="release-without-matching-custody-increase", severity=critical) BLOCK(claim) # PATH B — type-identity assertion on every parsed event record on parsed_event(record, expected_type): tag ← type_tag(record) # Anchor 8-byte discriminator | topic0 | protobuf type URL if tag = ∅ or tag ≠ discriminator_of(expected_type): emit(PATH_B, observer=record.observer, src_chain=record.chain, tx=record.tx, expected=expected_type, observed=tag, mode="event-type-tag-missing-or-mismatched", severity=critical) BLOCK(record) # PATH C — source-transaction value / status sanity on observer_release_decision(claim): src ← source_transaction(claim.src_ref) if src.status = failed or value_moved_to(bridge_custody_account, src) = 0 or counterparties(src) ⊆ {claim.beneficiary_cluster}: # self-transfer emit(PATH_C, tx=src.hash, beneficiary=claim.beneficiary, mode="fill-against-zero-value-or-self-transfer", severity=critical) BLOCK(claim) # PATH D — reserve-depletion velocity (runtime backstop) for each window W of size depletion_window: outflows ← release_events(bridge_custody_account, in = W) shapes ← group_by(outflows, key = canonical_form(payment)) reserve_start ← custody_balance(bridge_custody_account, at = W.start) drawn ← Σ amount for outflows if drawn ≥ depletion_fraction × reserve_start or (max(|s| for s in shapes.values()) ≥ same_shape_count and drawn ≥ depletion_floor): emit(PATH_D, bridge_custody_account, window=W, drawn=drawn, reserve_fraction=drawn/reserve_start, mode="reserve-depletion-velocity", severity=critical) parameters: reconcile_tolerance: { type: number, default: 0 } # exact by default; fees handled out-of-band depletion_window: { type: duration, default: 2h } depletion_fraction: { type: number, default: 0.25 } # 25% of reserve in one window same_shape_count: { type: integer, default: 20 } # Coreum drew 94 same-shaped payments depletion_floor: { type: number, default: 25000 } # absolute USD floor observer_quorum: { type: integer, default: 2 } # independent observers that must agree pre-release output_alert: [oak_technique, detection_path, severity, chain, bridge_custody_account, observer, tx, mode, evidence] test_fixtures: positive: - 2026-07-across-solana-relayer-anchor-event-discriminator-forgery # parse-level: unchecked Anchor discriminator, 1,627 forged deposits - 2026-08-coreum-xrpl-bridge-forged-deposit-memo-relayer-verification # semantic: memo trusted, XRP receipt never confirmed, 94 payments / 97 min negative: - "Legitimate high-volume filler activity where every fill maps to a source transaction that moved funds into custody" - "Bridge reserve rebalancing by the operator — outflow present, but custody invariant preserved across the paired accounts" - 2026-07-layerzero-executor-multi-chain-simultaneous-wallet-drain # NOT this Technique: the observer's own hot keys were stolen (T11.011); no source event was forged - 2026-05-verus-ethereum-bridge-source-amount-validation # NOT this Technique: the missing conservation check was in deployed bytecode (parent T10.002) false_positive_modes: - fee-adjusted settlement where the custody increase legitimately trails the credited amount by a protocol fee (PATH A's reconcile_tolerance, or reconcile net-of-fee) - batched deposits reconciled asynchronously, so custody rises after the credit decision — restructure as reserve-then-release rather than widening the tolerance - source-chain reorg temporarily inverting the custody delta; re-evaluate on finality rather than on inclusion - operator-initiated treasury migration draining the custody account by design (PATH D — allowlist the operator's own destination cluster) - "chains whose event model has no type tag at all: PATH B is unavailable and PATH A must carry the whole load" mitigations: [OAK-M11, OAK-M12, OAK-M16, OAK-M34, OAK-M36, OAK-M38, OAK-M39] reference_implementations: - { target: forta-bot, chain: evm, url: "" } - { target: oz-defender-sentinel, chain: evm, url: "" } - { target: dune, chain: evm, url: "" } - { target: anchor-discriminator, chain: solana, url: "" }