Smart Contract Audit

When to activate

• Auditing Solidity or Vyper contracts before deployment
• Reviewing DeFi protocol code for economic attack vectors
• Checking upgradeable proxy patterns for storage collisions
• Evaluating access control patterns across a contract system
• Preparing for a professional security audit engagement

When NOT to use

• For off-chain application code (use standard code review)
• For blockchain explorer or indexer code
• For frontend Web3 dApp code

Instructions

1. Map attack surface. List all external-facing functions. Identify state-modifying functions. Map call paths to sensitive operations (transfers, mints, admin actions).

2. Check critical vulnerabilities:

   • Reentrancy: External calls before state updates? Use checks-effects-interactions. CEI pattern.
   • Access control: Missing onlyOwner/role checks? Unprotected selfdestruct? Unrestricted delegatecall?
   • Integer overflow: Pre-0.8.0 without SafeMath? Underflow in balance calculations?
   • Oracle manipulation: Using spot prices from DEX as oracle? Flash loan price manipulation?
   • Front-running: Transaction ordering dependencies? Sandwich attack vectors?
   • Denial of service: Unbounded loops? External calls in loops? Push vs pull payments?

3. Review economic logic. Does the math preserve invariants? Total supply == sum of balances? Collateral ratio maintained?

4. Check upgrade patterns. Proxy storage layout matches? Function selectors don't collide? Initializer called?

5. Generate audit report. Severity: Critical, High, Medium, Low, Informational. Include PoC for critical findings.

Example

Audit Finding: CRITICAL — Reentrancy in withdraw()

Contract: Vault.sol, Line 42
Issue: Ether transfer occurs before balance update.

Vulnerable:
  function withdraw() external {
    uint amount = balances[msg.sender];
    (bool ok,) = msg.sender.call{value: amount}(""); // external call first
    require(ok);
    balances[msg.sender] = 0; // state update after
  }

Fix:
  function withdraw() external nonReentrant {
    uint amount = balances[msg.sender];
    balances[msg.sender] = 0; // state update first (effects)
    (bool ok,) = msg.sender.call{value: amount}(""); // external call last
    require(ok, "Transfer failed");
  }