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Security patterns · hard

43. Front-running and MEV considerations

Designing functions that resist transaction-ordering attacks.

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Any function whose outcome depends on being executed first (e.g. claiming a fixed-price opportunity, or a naive auction) is vulnerable to front-running: someone watching the mempool copies or outbids your transaction with higher gas to land first.

# Vulnerable: price depends on execution order
@external
def buy(min_amount: uint256):
    # if pool price can move between submission and execution,
    # an attacker can sandwich this trade
    ...

Mitigations include slippage/minimum-output parameters (as above), commit-reveal schemes for sensitive actions, and using private mempools/relays for especially sensitive transactions.

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Check your understanding

  1. 1. What makes a transaction vulnerable to front-running?

  2. 2. What parameter commonly mitigates front-running in trades?

  3. 3. What is a commit-reveal scheme used for?

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