Glossary definition

Front-running

Front-running is transaction ordering that places an actor's transaction before a known pending action to profit from or change its outcome.

also: transaction-ordering attack, priority gas auction · reviewed July 22, 2026

On a public mempool, transaction intent can be visible before inclusion. A searcher, validator, or builder may submit or order another transaction first. Sandwich trading is a familiar example, but ordering can also capture claims, invalidate quotes, win auctions, or alter governance and liquidation outcomes.

Mitigations depend on the mechanism: commit–reveal schemes, private order flow, batch auctions, signed limits, minimum outputs, deadlines, and designs that do not award value to the first visible caller. The migrated MGF case study shows how a stateful test can expose a specific instance.