iktok90-design/ai-smart-contract-auditor/erc4337-account-abstraction

ERC-4337 / Account Abstraction detection

When this applies

• Smart-wallet implementations (SimpleAccount, Safe-AA, Kernel, Biconomy, Light Account, custom)
• Paymaster contracts (verifying, deposit, token-paying, sponsorship)
• Module systems (ERC-7579, ERC-6900) and session-key managers
• Bundler / mempool-side relayer logic (rare in app code, but watch for)
• EIP-7702 delegated EOAs

Detection patterns

validateUserOp storage-rule violation (HIGH)

ERC-4337 §6 forbids SLOAD on storage slots outside the wallet's own contract during validation. Bundlers reject non-compliant UserOps. Beyond compliance, accessing external state during validate is a banner attack surface (e.g. reading from an attacker-controlled contract).

function validateUserOp(...) external returns (uint256) {
    uint256 x = IExternal(0xabc).read();   // ← violates storage rules + leaks attack surface
    ...
}

Missing msg.sender == entryPoint() check (CRITICAL)

function validateUserOp(...) external returns (uint256) {
    // ← anyone can call directly, bypass bundler entirely
}

Paymaster postOp revert risk (HIGH)

function postOp(PostOpMode mode, bytes calldata ctx, uint256 actualGasCost) external {
    require(...);   // ← if this reverts in postOp, bundler is griefed; reputation system penalizes the paymaster
}

postOp should be revert-free. Use try/catch or never revert.

Paymaster oracle manipulation for token-paying (HIGH)

Token-paying paymaster converts ERC20 → ETH at validate time. If oracle is spot AMM, sandwichable. See [[oracle-manipulation]].

Sponsorship-paymaster missing nonce/deadline (HIGH)

Sponsorship sig replayable. See [[signature-replay]].

Session-key scope bypass (HIGH)

Session keys grant limited authority (allowed selectors, allowed targets, time bounds). Bypass paths:

• Multicall router that the session key approves → key calls arbitrary fns via the router
• Fallback function not scoped
• ERC-7579 module installation while session-key active
• Approval to swap router → token-drain via the approval

EIP-7702 chainId-less authorization (CRITICAL)

EIP-7702 delegations replayable across chains if chainId == 0 or missing chainId binding.

EIP-7702 delegation to attacker (CRITICAL)

User signs an authorization to a contract address. If that contract is upgradeable / attacker-controlled, the EOA's nonce-aware delegated-call grants full control.

Aggregated sig replay (HIGH)

BLS-aggregated UserOps with aggregator field — if aggregator's verifier doesn't include chainId, cross-chain replay possible.

Nonce-key collision (MEDIUM)

ERC-4337 uses 192-bit "nonce-key" for parallel UserOps. If multiple session keys / dapps share key 0, they serialize unnecessarily. Worse: if key encoding collides with another semantic, a stuck UserOp can DoS.

Permit2 + AA collision (MEDIUM)

Meta-tx with permit can collide on nonces with regular UserOp.

Module install with missing auth check (CRITICAL)

ERC-7579 / ERC-6900 module install paths sometimes lack onlyEntryPointOrOwner. Install path → arbitrary module → arbitrary execution.

Severity rubric

Remediation patterns

• Wallet: require(msg.sender == address(entryPoint()), "only EP");.
• Paymaster: never revert in postOp; use try/catch internally.
• Module install: gate behind onlyEntryPointOrOwner and a per-module validation step.
• Session keys: explicit allowlist of (selector, target) tuples; no fallback fallthrough.
• EIP-7702: include chainId in EIP-7702 authorization payload; delegate only to immutable, audited code.
• Storage rules: only SLOAD from self during validate; cache external state into self-state before validate.

False-positive notes

• Canonical SimpleAccount-style impls from eth-infinitism are reference; safe.
• "Account Factory" pre-deployment patterns sometimes look risky but are well-understood.

Related

• [[signature-replay]]
• [[delegatecall-risks]]
• [[aa-specialist]] (subagent)