Overview
Direct Answer
A flash loan is an uncollateralised loan in decentralised finance (DeFi) that must be borrowed and repaid within a single atomic blockchain transaction, with no intermediary risk management or upfront collateral requirement. The loan is automatically reversed if repayment plus fees is not executed before the transaction completes.
How It Works
Flash loans operate through smart contract logic that executes three sequential steps within one transaction: funds are transferred to the borrower, the borrower executes arbitrary logic (such as arbitrage or collateral swaps), and the original amount plus a protocol fee is returned to the lender. If any step fails or the repayment condition is not met, the entire transaction reverts atomically, protecting the lender without requiring collateral upfront.
Why It Matters
Flash loans reduce friction in capital-constrained DeFi operations by eliminating collateral requirements and enabling participants to execute complex transactions with temporary liquidity. They are economically significant for arbitrage optimisation, liquidation strategies, and protocol testing, driving efficiency in decentralised markets where traditional credit mechanisms are impractical.
Common Applications
Flash loans are utilised in decentralised exchange arbitrage, collateral swaps across lending protocols, and liquidation of undercollateralised positions. They have also been employed for protocol auditing and exploit testing by security researchers.
Key Considerations
Flash loan attacks have exploited price oracle vulnerabilities and insufficient validation logic in receiving smart contracts, highlighting the necessity for robust transaction validation and decentralised price feeds. The mechanism's utility depends entirely on transaction atomicity and the receiver contract's ability to enforce repayment conditions.
Cross-References(1)
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