LibraryCredit and stable value2020Design paperCorpus record
ERC-3156: Flash Loans
Flash loans. Alberto Cuesta Cañada, Fiona Kobayashi, fubuloubu, Austin Williams.
A flash lender sends assets to a receiver and requires that the same transaction returns them, plus a fee. If it does not, the transaction reverts. There is no default in the credit sense, because there is no time.
A reading of the public document. Not a copy of it, and not a claim about a later network that reused the name.
An oracle that can be moved and restored inside one transaction is compatible with this primitive. That is the risk to design against.
The five-minute read
The defect
A loan that must be repaid in the same transaction is either impossible, in a human process, or a primitive, in an atomic chain.
The rule
A flash lender sends assets to a receiver and requires that the same transaction returns them, plus a fee. If it does not, the transaction reverts. There is no default in the credit sense, because there is no time.
How it is put together
The loan and the repayment are one transaction. The lender's check is at the end. Failure reverts. It does not create a bad debt inside this interface.
Where the claim stops
The standard does not invent the attack. It names the interface.
One action, walked through
- The receiver asks for an amount.
- The lender sends it and calls the receiver.
- The receiver must return the amount and the fee before the lender's function finishes.
- Does repayment happen before the transaction can end?
The argument, unpacked
Why it is still on the desk
An oracle that can be moved and restored inside one transaction is compatible with this primitive. That is the risk to design against.
After the text
Aave and others shipped flash loans before the ERC. The ERC is the common shape.
What has to be true
- The standard does not invent the attack. It names the interface.
- A flash loan can still be used to manipulate a price in the same transaction.
- It is not a revolving credit line.
What happened after the paper
Aave and others shipped flash loans before the ERC. The ERC is the common shape.
What to check before you use the idea
- Does repayment happen before the transaction can end?
- What fee is charged if it does?
- Which external price can be moved inside the same call?
Terms
- Receiver
- The contract that is handed the assets and must return them.
- Atomic
- One transaction. No later repayment exists.
The problem the paper names
A loan that must be repaid in the same transaction is either impossible, in a human process, or a primitive, in an atomic chain.
What the design proposes
- The loan and the repayment are one transaction.
- The lender's check is at the end.
- Failure reverts. It does not create a bad debt inside this interface.
How the mechanism is specified
- The receiver asks for an amount.
- The lender sends it and calls the receiver.
- The receiver must return the amount and the fee before the lender's function finishes.
What this page does not treat as proven
- The standard does not invent the attack. It names the interface.
- A flash loan can still be used to manipulate a price in the same transaction.
- It is not a revolving credit line.
Why a venture studio still reads it
An oracle that can be moved and restored inside one transaction is compatible with this primitive. That is the risk to design against.
This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.
Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.