feat(checks): ERC-777 reentrancy via tokensReceived hook (closes #19)#26
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Adds a check + vulnerable fixture for the ERC-777 tokensReceived reentrancy class — the same vulnerability that drained imBTC and Uniswap V1 in April 2020 ($340K) and several smaller venues since. The bug class is identical to classic ETH reentrancy, but routes through the ERC-777 recipient hook instead of receive(). Tools that look only for low-level receive() callbacks miss it. New files: - src/checks/ERC777ReentrancyCheck.sol — abstract check + attacker - src/examples/VulnerableERC777Vault.sol — fixture: mock ERC-777 token (hook-on-transfer) + vault that pays out before settling - test/ERC777Reentrancy.t.sol — example wiring (excluded from CI forge test per ci.yml --no-match-contract '^(Example|...)'; this is a demo, not an invariant — drained-balance > deposit triggers fail() so the run surfaces the bug) Override hooks parallel ReentrancyCheck.sol: getWithdrawCalldata() / getERC777Token() / getDepositValue() / performDeposit(address, uint256)
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| function withdraw() external { | ||
| uint256 owed = deposits[msg.sender]; | ||
| require(owed > 0, "no deposit"); | ||
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| // External call (with hook) BEFORE state update — vulnerable. | ||
| token.transfer(msg.sender, owed); | ||
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| deposits[msg.sender] = 0; // Too late — attacker already re-entered. | ||
| } |
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| /// @dev Attacker contract. Re-enters `withdraw` via the tokensReceived hook. | ||
| contract ERC777ReentrantAttacker is IERC777Recipient { | ||
| address public target; |
| address public target; | ||
| bytes public payload; | ||
| uint256 public reentries; | ||
| uint256 public maxReentries = 2; |
| /// (recipient hook before settlement) are identical. | ||
| contract MockERC777Token { | ||
| mapping(address => uint256) public balanceOf; | ||
| string public name = "Mock 777"; |
| contract MockERC777Token { | ||
| mapping(address => uint256) public balanceOf; | ||
| string public name = "Mock 777"; | ||
| string public symbol = "M777"; |
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| function withdraw() external { | ||
| uint256 owed = deposits[msg.sender]; | ||
| require(owed > 0, "no deposit"); | ||
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| // External call (with hook) BEFORE state update — vulnerable. | ||
| token.transfer(msg.sender, owed); | ||
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| deposits[msg.sender] = 0; // Too late — attacker already re-entered. | ||
| } |
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Summary
Adds a check + vulnerable fixture for the ERC-777
tokensReceivedreentrancy class — the same bug that drained imBTC and Uniswap V1 in April 2020 (~$340K). It is structurally identical to classic ETH reentrancy but routes through the ERC-777 recipient hook, so detectors that only watch for low-levelreceive()callbacks miss it.Closes #19.
Files
src/checks/ERC777ReentrancyCheck.sol— abstract check, mirrorsReentrancyCheck.sol's shape; attacker reimplementsIERC777Recipient.tokensReceivedsrc/examples/VulnerableERC777Vault.sol— minimalMockERC777Token(callstokensReceivedon contract recipients) +VulnerableERC777Vault(pays before settling balance)test/ERC777Reentrancy.t.sol— example audit harness wiring check ↔ vaultOverride hooks
getWithdrawCalldata()getERC777Token()tokensReceivedis hookedgetDepositValue()performDeposit(address, uint256)CI behavior
ExampleERC777ReentrancyAuditmatches the existing^(Example|TestERC4626)exclusion in.github/workflows/audit.yml. The example is a demo-of-detection (it callsfail()when the vulnerability is detected — that is the check working), not a runnable invariant.forge buildstill validates compilation.Test plan
forge buildsucceedsforge test --no-match-contract '^(Example|TestERC4626)'stays greenforge test --match-contract ExampleERC777ReentrancyAudit -vvvshows the vulnerability detection lognonReentrant) → check passes