front-running-patterns

Front-Running & MEV Patterns

What Is MEV?

Maximal Extractable Value (MEV) is the profit extractable by reordering, inserting, or censoring transactions within a block. Validators and searchers extract MEV through:

• Sandwich attacks: front-run + back-run a victim's swap
• Front-running: copy a profitable transaction and get it mined first
• Back-running: execute immediately after a target transaction
• Liquidation racing: compete to liquidate undercollateralized positions
• Just-in-Time (JIT) liquidity: add/remove concentrated liquidity around a trade

Sandwich Attacks on Swaps

1. Victim submits swap: buy 100 ETH of TOKEN
2. Attacker front-runs: buys TOKEN, pushing price up
3. Victim's swap executes at worse price
4. Attacker back-runs: sells TOKEN at inflated price

Defense: Slippage Protection

error SlippageExceeded(uint256 amountOut, uint256 minAmountOut);

function swap(
    address tokenIn,
    address tokenOut,
    uint256 amountIn,
    uint256 minAmountOut,   // user sets minimum acceptable output
    uint256 deadline
) external returns (uint256 amountOut) {
    if (block.timestamp > deadline) revert Expired();

    amountOut = _executeSwap(tokenIn, tokenOut, amountIn);

    if (amountOut < minAmountOut) {
        revert SlippageExceeded(amountOut, minAmountOut);
    }

    emit Swapped(msg.sender, tokenIn, tokenOut, amountIn, amountOut);
}

Defense: Deadline Parameters

Without deadlines, pending transactions can be held in the mempool and executed later at unfavorable prices.

modifier beforeDeadline(uint256 deadline) {
    if (block.timestamp > deadline) revert TransactionExpired(deadline, block.timestamp);
    _;
}

function addLiquidity(
    uint256 amount0,
    uint256 amount1,
    uint256 minLiquidity,
    uint256 deadline
) external beforeDeadline(deadline) returns (uint256 liquidity) {
    // ...
}

Commit-Reveal Scheme

For auctions, NFT mints, or any scenario where knowing the action gives an advantage.