A flash loan is an uncollateralized loan unique to DeFi: you can borrow a large amount of crypto with no upfront collateral, as long as you borrow and repay it within the same blockchain transaction. If the loan isn’t repaid by the end of that transaction, the entire transaction is automatically reversed as if it never happened.
Key Takeaways
- Flash loans require no collateral, but must be borrowed and repaid within a single blockchain transaction — if repayment fails, the whole transaction reverts.
- This atomic structure is what makes uncollateralized lending safe for the lender: there’s no possibility of a partial default.
- Legitimate use cases include arbitrage, collateral swapping, and efficiently closing out leveraged positions.
- Flash loans have also been used as an attack tool — borrowing a large sum to manipulate a protocol’s pricing or governance within a single transaction.
- Using flash loans directly typically requires writing custom smart contract code, making them a tool mostly used by developers and sophisticated traders.
Our Take
Flash loans are one of the more genuinely novel financial primitives DeFi has produced — the concept of borrowing millions of dollars with zero collateral, made possible entirely by the atomic, all-or-succeed-or-nothing nature of blockchain transactions, has no real precedent in traditional finance.
The attack use cases are a real and recurring problem specifically because flash loans let an attacker temporarily command enormous capital without needing to actually own it, which can be enough to manipulate a poorly designed protocol’s price oracle or governance vote.
FAQs
Do I need collateral for a flash loan?
No — instead of collateral, the loan is secured by the requirement that it be borrowed and repaid within the same blockchain transaction, or the entire transaction is reversed.
Can I use flash loans as an average retail user?
Not easily — using a flash loan typically requires writing custom smart contract code, making it mostly a tool for developers and sophisticated traders.
📎 Source: Coinbase Learn — What is a flash loan?
