iktok90-design/ai-smart-contract-auditor/intents-erc7683

Intent-based / ERC-7683 detection

When this applies

• ERC-7683 cross-chain intents
• UniswapX (reactor + filler model)
• CoW Protocol (batch auctions)
• 1inch Fusion / Fusion+
• Across (origin lock + destination fill)
• Any "user signs intent, solver fills" pattern

Detection patterns

Surplus theft (HIGH)

Intent specifies amountOutMin (user's floor). Solver delivers exactly the min, pockets actual market surplus. UX issue but real for intents with tight min — solver fills inferior route. Defense: surplus distribution to user (CoW does this).

Cross-chain replay (HIGH)

ERC-7683 intent payload signable for one (origin, destination) pair must include both chainIds. Otherwise replay on another destination.

Solver front-run (HIGH)

Solver A's fill is in mempool; Solver B copies and submits with higher gas → A's tx reverts. Mitigations: private mempools, MEV-Share, exclusivity windows.

Intent expiration not enforced atomically (HIGH)

require(block.timestamp <= deadline) at settlement. If deadline is checked at the wrong step (e.g. at origin lock but not destination fill), funds can be stuck.

Origin lock + destination fill atomicity (CRITICAL)

• User locks funds on origin chain.
• Solver fills on destination chain.
• Solver claims locked funds on origin (via cross-chain proof).
• If destination fill fails after origin lock: refund mechanism required.
• If origin lock fails after destination fill: solver loses; bond required.

Reactor callback reentrancy (HIGH — UniswapX-specific)

reactor.execute(order, fillerCallback) → callback in attacker-controlled filler contract. If reactor state is mutated mid-callback, reentrancy possible. Required: nonReentrant on the reactor.

Permit2 + intent collision (HIGH)

Intent assumes user's Permit2 sig was just executed. Solver can race: front-run the permit, grief the intent.

Allowed-fillers list bypass (HIGH)

Intent restricts to specific solvers. If the list check is via tx.origin (instead of msg.sender or signature recovery), trivially bypassable.

Decay function correctness (HIGH — UniswapX)

Dutch auction: output token amount decays over time. If decay math overflows or rounds wrong, solver fills at the minimum before decay completes.

Salt-based nonce missing (HIGH)

Intent identifies itself by (user, salt). If salt isn't enforced unique on-chain, multiple identical intents replayable.

Solver bond on cross-chain (HIGH)

Cross-chain intents (ERC-7683): solver bonds on destination to prove they'll bring liquidity. If bond is too small, solver can grief by filling and abandoning.

Slow-path fallback (HIGH)

If fast solver doesn't fill: fallback to a slower, trustless path. Bug surface: race between fast and slow paths.

Cancellation race (HIGH)

User cancels intent (cancel); solver fills in the same block. Order-of-execution determines who wins. Required: cancel must invalidate fills in the same tx.

Severity rubric

Remediation patterns

• Always include both origin and destination chainIds in signed payload.
• Atomic origin lock + cross-chain message + destination fill OR atomic refund.
• nonReentrant on reactor.
• Solver-allowed-list via signature recovery against an allowlist set, not tx.origin.
• Surplus → user (CoW model).
• Bond sized to disincentivize griefing (≥ profit margin × N).
• Cancellation invalidates all in-flight fills atomically.

False-positive notes

• CoW / UniswapX reference implementations are well-audited.
• Solver-side bugs aren't in scope for the contract audit — call out as advisory.

Related

• [[intents-specialist]] (subagent)
• [[cross-chain-messaging]]
• [[mev-frontrunning]]
• [[permit2-patterns]]