Defi Security

DeFi Security Principles

Language Rule

• Always respond in the same language the user is using. If the user asks in Chinese, respond in Chinese. If in English, respond in English.

> Scope: Only applicable to DeFi projects (DEX, lending, staking, LP, yield). Non-DeFi projects can ignore this skill.

Protection Decision Rules

| Threat | Required Protection | |--------|-------------------| | Whale manipulation | Daily transaction caps + per-tx amount limits + cooldown window | | MEV / sandwich attack | EOA-only checks (msg.sender == tx.origin), or use commit-reveal pattern | | Arbitrage | Referral binding + liquidity distribution + fixed yield model + lock period | | Reentrancy | ReentrancyGuard on all external-call functions (see solidity-security skill) | | Flash loan attack | Check block.number change between operations, or use TWAP pricing | | Price manipulation | Chainlink oracle or TWAP — never rely on spot AMM reserves for pricing | | Approval exploit | Use safeIncreaseAllowance / safeDecreaseAllowance, never raw approve for user flows | | Governance attack | Voting requires snapshot + minimum token holding period; timelock ≥ 48h on proposal execution | | ERC4626 inflation attack | First deposit must enforce minimum amount or use virtual shares to prevent share dilution via rounding | | Cross-vault trust bypass | Router/Registry relay must verify vault authorization; never trust caller identity inside flash loan callbacks — EVMbench/noya H-08 | | Collateral ownership exploit | Liquidation/staking operations must verify actual NFT/collateral ownership — EVMbench/benddao | | Bonding curve manipulation | ID/pricing params in create operations must be fully determined before external calls — EVMbench/phi H-06 | | DEX pair _transfer TOCTOU | Never distinguish operation type by balance/reserve checks in _transfer — both directions are exploitable: buy vs removeLiquidity (pair→user) and sell vs addLiquidity (user→pair); use address whitelist only; new projects prefer Uniswap V4 Hook | | Per-address state bypass | Any mapping(address => ...) restriction (cooldown, max tx, max balance) can be bypassed via multi-address or transfer-then-trade; propagate restriction state on wallet-to-wallet transfers using max(_lastTxTime[to], _lastTxTime[from]) — never block.timestamp (griefing) or direct assignment (overwrite shortening) |

Anti-Whale Implementation Rules

• Maximum single transaction amount: configurable via onlyOwner setter
• Daily cumulative limit per address: track with mapping(address => mapping(uint256 => uint256)) (address → day → amount)
• Cooldown between transactions: enforce minimum time gap with block.timestamp check
• Whitelist for exempt addresses (deployer, LP pair, staking contract)

Flash Loan Protection Rules

• For price-sensitive operations: require that block.number has changed since last interaction
• For oracle-dependent calculations: use time-weighted average (TWAP) over minimum 30 minutes
• For critical state changes: add minimum holding period before action (e.g., must hold tokens for N blocks)

Protocol Composability Risks

> Source: EVMbench (OpenAI/Paradigm, Feb 2026) — vulnerability patterns from Code4rena audits

• Cross-vault operations [noya H-08]: Registry/Router relay calls must verify vault-level authorization; prevent keeper from using flash loan to impersonate other vaults
• Lending collateral [benddao]: Liquidation functions must verify msg.sender actually owns or is authorized to operate on target collateral
• Bonding curve [phi H-06]: In create + auto-buy operations, ID assignment and pricing params must be fully determined before the buy transaction executes; prevent reentrancy from modifying them
• Shared registries [noya H-08]: Permission propagation chains in shared registries must be verified hop-by-hop; never rely solely on "trusted sender" flags

Launch Checklist

Before mainnet deployment, verify all items:

• [ ] All onlyOwner functions transferred to multisig wallet
• [ ] Timelock contract deployed and configured (minimum 24h delay for critical changes)
• [ ] Emergency pause mechanism tested — both pause and unpause functions work correctly
• [ ] Daily limit parameters documented and set to reasonable values
• [ ] Third-party security audit completed and all critical/high findings resolved
• [ ] Testnet deployment running for minimum 7 days with no issues
• [ ] Slippage, fee, and lock period parameters reviewed and documented
• [ ] Initial liquidity plan documented (amount, lock duration, LP token handling)
• [ ] Fuzz testing passes with high iterations (10000+) on all DeFi-critical functions

Emergency Response Procedure

| Step | Action | |------|--------| | 1. Detect | Monitor alerts trigger (on-chain monitoring, community reports) | | 2. Pause | Designated address calls pause() — must respond within minutes | | 3. Assess | Technical lead analyzes root cause, estimates fund impact | | 4. Communicate | Post incident notice to community channels (Discord, Twitter, Telegram) | | 5. Fix | Deploy fix or prepare recovery plan | | 6. Resume | Call unpause() after fix verified on fork — or migrate to new contract | | 7. Post-mortem | Publish detailed incident report within 48 hours |

DeFi Testing Reference

| Test Scenario | Approach | |---------------|----------| | Fuzz test fund flows | Run fuzz tests on staking/pool contracts with high iterations (10000+) | | Fork mainnet testing | Use Foundry fork mode against mainnet RPC to test with real state | | Simulate whale transaction | Use Foundry cast CLI to simulate large-amount calls on a forked network |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: 0xlayerghost
• Source: 0xlayerghost/solidity-agent-kit
• License: MIT
• Homepage: https://skills.sh/0xlayerghost/solidity-agent-kit/solidity-coding

Install and usage instructions live in the source repository linked above.