Smart Contract Audit

Smart Contract Audit

A smart contract audit is not a formal checkmark before mainnet. It is the only real opportunity to find vulnerabilities before attackers do. Vulnerabilities in contracts cannot be patched silently: exploits are public, losses are instantaneous, reputational damage is permanent. Ronin Bridge ($625M), Wormhole ($320M), Euler Finance ($197M) — all these hacks occurred in codebases reviewed by development teams. A fresh perspective from professional auditors is not a luxury.

What a Full Audit Includes

An audit is not just running automatic analyzers. Mechanical tools (Slither, Mythril, Echidna) find 30–40% of vulnerabilities; the rest requires manual logic analysis.

Manual code review: line-by-line analysis of each function, verification of business logic against specification. Most critical vulnerabilities are not technical patterns like reentrancy, but logic errors.

Automated analysis: Slither (static analysis), Mythril (symbolic execution), Echidna (fuzzing). Forms the basis for manual analysis, finds low-hanging fruit.

Test cases for vulnerabilities: for each found issue, a Proof of Concept is formulated — code that reproduces the exploit.

Gas optimization: parallel to security — analysis of inefficient patterns (storage vs memory, unnecessary SLOAD/SSTORE, excessive events).

Vulnerability Classification

Top Vulnerabilities 2023–2024

Reentrancy: classic, but still encountered. External call before state update allows recursive contract draining. Checks-effects-interactions pattern + ReentrancyGuard.

Price oracle manipulation: flash loans allow spot price AMM manipulation. Using TWAP (time-weighted average price) instead of spot price is mandatory protection for any lending protocol.

Access control: onlyOwner instead of role-based access control, missing timelock on critical functions, incorrect msg.sender checks in proxy patterns.

Signature replay: signature intended for one contract/network used in another. EIP-712 domain separator + nonce — standard protection.

// Example vulnerable code — signature without nonce and domain
function claimReward(bytes memory signature, uint256 amount) external {
    bytes32 hash = keccak256(abi.encodePacked(msg.sender, amount));
    require(recoverSigner(hash, signature) == trustedSigner, "Invalid sig");
    token.transfer(msg.sender, amount);
    // VULNERABILITY: no nonce, same signature works repeatedly
    // VULNERABILITY: no domain, signature portable to other contracts
}

// Fixed version with EIP-712
function claimReward(bytes memory signature, uint256 amount, uint256 nonce) external {
    require(!usedNonces[nonce], "Nonce used");
    
    bytes32 structHash = keccak256(abi.encode(
        CLAIM_TYPEHASH,
        msg.sender,
        amount,
        nonce
    ));
    bytes32 digest = _hashTypedDataV4(structHash);  // EIP-712 domain included
    require(ECDSA.recover(digest, signature) == trustedSigner, "Invalid sig");
    
    usedNonces[nonce] = true;
    token.transfer(msg.sender, amount);
}

Audit Process

Phase 1 — Onboarding (1–2 days): documentation from the team (specification, architectural diagrams, business logic description). The better the documentation — the more efficient the audit.

Phase 2 — Manual review (5–10 days): auditors immerse in code. Minimum two independent reviewers per contract.

Phase 3 — Automated analysis (parallel): Slither, Mythril, custom Echidna properties.

Phase 4 — Draft report (2–3 days): formulation of preliminary report with all findings.

Phase 5 — Remediation review (3–5 days): team fixes, auditors verify fixes. Critical findings require re-verification.

Phase 6 — Final report: public report with description of all findings and fix statuses.

Cost and Timeline

Audit cost depends on code volume (lines of Solidity), logic complexity, and auditor reputation. Top-tier auditors (Trail of Bits, OpenZeppelin, Spearbit, Code4rena) — $30,000–200,000+ per project. Mid-level — $10,000–40,000. Timeline: 1–4 weeks.

Competitive audits (Code4rena, Sherlock, Cantina) — alternative or supplement: public competition, hundreds of auditors, but uneven coverage and no guarantee of critical function depth.

For most DeFi projects, optimal: one full private audit + public contest for broad coverage.