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

2. Mitigation

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

3. 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