Smart Contract Security Skill

Master smart contract security with vulnerability detection, auditing methodology, and incident response procedures.

Quick Start

Invoke this skill for security analysis

Skill("smart-contract-security", topic="vulnerabilities", severity="high")

Topics Covered 1. Common Vulnerabilities

Recognize and prevent:

Reentrancy: CEI pattern violation Access Control: Missing modifiers Oracle Manipulation: Flash loan attacks Integer Issues: Precision loss 2. Auditing Methodology

Systematic review process:

Manual Review: Line-by-line analysis Static Analysis: Automated tools Fuzzing: Property-based testing Formal Verification: Mathematical proofs 3. Security Tools

Essential tooling:

Slither: Fast static analysis Mythril: Symbolic execution Foundry: Fuzzing, invariants Certora: Formal verification 4. Incident Response

Handle security events:

Triage: Assess severity Mitigation: Emergency actions Post-mortem: Root cause analysis Disclosure: Responsible reporting Vulnerability Quick Reference Critical: Reentrancy // VULNERABLE function withdraw(uint256 amount) external { (bool ok,) = msg.sender.call{value: amount}(""); require(ok); balances[msg.sender] -= amount; // After call! }

// FIXED: CEI Pattern function withdraw(uint256 amount) external { balances[msg.sender] -= amount; // Before call (bool ok,) = msg.sender.call{value: amount}(""); require(ok); }

High: Missing Access Control // VULNERABLE function setAdmin(address newAdmin) external { admin = newAdmin; // Anyone can call! }

// FIXED function setAdmin(address newAdmin) external onlyOwner { admin = newAdmin; }

High: Unchecked Return Value // VULNERABLE IERC20(token).transfer(to, amount); // Ignored!

// FIXED: Use SafeERC20 using SafeERC20 for IERC20; IERC20(token).safeTransfer(to, amount);

Medium: Precision Loss // VULNERABLE: Division before multiplication uint256 fee = (amount / 1000) * rate;

// FIXED: Multiply first uint256 fee = (amount * rate) / 1000;

Audit Checklist Pre-Audit Code compiles without warnings Tests pass with good coverage Documentation reviewed Core Security CEI pattern followed Reentrancy guards present Access control on admin functions Input validation complete DeFi Specific Oracle staleness checks Slippage protection Flash loan resistance Sandwich prevention Security Tools Static Analysis

Slither - Fast vulnerability detection

slither . --exclude-dependencies

Mythril - Symbolic execution

myth analyze src/Contract.sol

Semgrep - Custom rules

semgrep --config "p/smart-contracts" .

Fuzzing // Foundry fuzz test function testFuzz_Withdraw(uint256 amount) public { amount = bound(amount, 1, type(uint128).max);

vm.deal(address(vault), amount);
vault.deposit{value: amount}();

uint256 before = address(this).balance;
vault.withdraw(amount);

assertEq(address(this).balance, before + amount);

}

Invariant Testing function invariant_BalancesMatchTotalSupply() public { uint256 sum = 0; for (uint i = 0; i < actors.length; i++) { sum += token.balanceOf(actors[i]); } assertEq(token.totalSupply(), sum); }

Severity Classification Severity Impact Examples Critical Direct fund loss Reentrancy, unprotected init High Significant damage Access control, oracle manipulation Medium Conditional impact Precision loss, timing issues Low Minor issues Missing events, naming Incident Response 1. Detection

Monitor for suspicious activity

cast logs --address $CONTRACT --from-block latest

1. Mitigation // Emergency pause function pause() external onlyOwner { _pause(); }

2. Recovery Assess damage scope Coordinate disclosure Deploy fixes with audit Common Pitfalls Pitfall Risk Prevention Only testing happy path Missing edge cases Fuzz test boundaries Ignoring integrations External call risks Review all dependencies Trusting block.timestamp Miner manipulation Use for long timeframes only Cross-References Bonded Agent: 06-smart-contract-security Related Skills: solidity-development, defi-protocols Resources SWC Registry: Common weakness enumeration Rekt News: Hack post-mortems Immunefi: Bug bounties Version History Version Date Changes 2.0.0 2025-01 Production-grade with tools, methodology 1.0.0 2024-12 Initial release