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Implements comprehensive helper system for testing protocols against non-standard ERC20 token behaviors. Addresses GitHub issue crytic#20. ## Overview Creates `ERC20EdgeCases` helper that deploys 20 different ERC20 token implementations, each exhibiting specific non-standard behaviors found in real tokens. This enables developers to test their protocols (DEXs, vaults, lending platforms) against all known ERC20 edge cases with a single import. ## Created Files (23 total) ### Core Helper (1 file) - **ERC20EdgeCases.sol**: Main helper contract that deploys all tokens and provides accessor functions: - `all_erc20()` - returns all 20 token addresses - `all_erc20_standard()` - returns only standard-compliant tokens - `all_erc20_non_standard()` - returns only non-standard tokens - `tokenByName(string)` - get specific token by name (e.g., "USDT-like") - Category helpers: `tokens_with_fee()`, `tokens_reentrant()`, etc. ### Token Implementations (20 files) Each token is a complete, working ERC20 with one specific edge case behavior: **Missing Return Values:** - MissingReturns.sol - No return value (USDT, BNB, OMG) - ReturnsFalse.sol - Returns false on success (Tether Gold) **Fee on Transfer:** - TransferFee.sol - Charges fee on transfer (STA, PAXG) - caused $500k Balancer drain **Reentrant Callbacks:** - Reentrant.sol - ERC777-style hooks (AMP, imBTC) - caused Uniswap/lendf.me drains **Admin Controls:** - BlockList.sol - Admin blocklist (USDC, USDT) - Pausable.sol - Admin pause (BNB, ZIL) **Transfer Quirks:** - RevertZero.sol - Reverts on zero transfers (LEND) - RevertToZero.sol - Reverts on transfer to address(0) (OpenZeppelin) - NoRevert.sol - Returns false instead of reverting (ZRX, EURS) - TransferFromSelf.sol - Doesn't decrease allowance if from == msg.sender (DSToken, WETH) - TransferMax.sol - Transfers full balance if amount == max uint256 (cUSDCv3) **Approval Quirks:** - ApprovalRaceProtection.sol - Can't change non-zero allowance (USDT, KNC) - ApprovalToZeroAddress.sol - Reverts on approve(address(0), amt) (OpenZeppelin) - RevertZeroApproval.sol - Reverts on approve(spender, 0) (BNB) - Uint96.sol - Reverts if amount >= 2^96 (UNI, COMP) **Metadata Quirks:** - Bytes32Metadata.sol - name/symbol as bytes32 (MKR) - LowDecimals.sol - 6 decimals (USDC) or 2 decimals (Gemini USD) - HighDecimals.sol - 24 decimals (YAM-V2) **Permit Issues:** - PermitNoOp.sol - permit() doesn't revert but does nothing (WETH) - caused Multichain hack **Baseline:** - StandardERC20.sol - Compliant implementation for comparison ### Documentation (1 file) - **README.md**: Comprehensive guide covering: - All 20 token types with real-world examples - Usage patterns and best practices - Real exploits that would have been prevented - Integration with Echidna/Medusa - Code examples for common testing scenarios ### Example Test Harness (1 file) - **tests/ERC20EdgeCases/ExampleVaultTest.sol**: Complete example showing: - Testing vault with all token types - Testing specific edge cases (fee tokens, reentrant tokens) - Proper accounting that handles fee-on-transfer - SafeERC20-style handling of missing return values - Example vault implementation with correct edge case handling ## Usage ```solidity import "@crytic/properties/contracts/util/erc20/ERC20EdgeCases.sol"; contract MyProtocolTest { ERC20EdgeCases edgeCases; constructor() { edgeCases = new ERC20EdgeCases(); } function test_protocolWithAllTokens() public { address[] memory tokens = edgeCases.all_erc20(); for (uint i = 0; i < tokens.length; i++) { // Test your protocol with each token } } } ``` ## Real-World Exploits Prevented This helper would have caught: - **Balancer STA Exploit (2020)**: $500k drained via fee-on-transfer tokens - **imBTC Uniswap Pool Drain**: Reentrancy via ERC777 hooks - **lendf.me Hack**: $25M stolen via reentrancy - **Multichain Hack**: Assumed permit succeeded without checking allowance - **Countless integration bugs**: Missing return values, approval race conditions, etc. ## Integration Points - Updated CLAUDE.md with new section on ERC20 edge case testing - Follows existing project patterns (NatSpec, testing structure) - Compatible with Echidna/Medusa fuzzing workflows - Complementary to existing ERC20 property tests (tests implementations vs. integrations) ## References - GitHub issue crytic#20: Create helpers for non-standard ERC20 - weird-erc20 repository: https://github.com/d-xo/weird-erc20 - Trail of Bits token integration checklist - All tokens based on real-world examples with documented exploits Closes crytic#20
omarinuwa
requested review from
bsamuels453 and
glarregay-tob
as code owners
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Implements comprehensive helper system for testing protocols against non-standard ERC20 token behaviors. Addresses issue #20.
Overview
Creates
ERC20EdgeCaseshelper that deploys 20 different ERC20 token implementations, each exhibiting specific non-standard behaviors found in real tokens. This enables developers to test their protocols against all known ERC20 edge cases with a single import.