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code-423n4 / 2022-02-hubble-findings

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After debt seizure from InsuranceFund, user can dilute all past participants. #129

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

Lines of code

https://github.com/code-423n4/2022-02-hubble/blob/ed1d885d5dbc2eae24e43c3ecbf291a0f5a52765/contracts/InsuranceFund.sol#L56

Vulnerability details

Impact

A user can get a much larger portion of the pool as it recovers from a debt seizure. The intent of the insurance pool seems to be that it could recover from a bad debt event.

Proof of Concept

  1. Alice is the first LP to the insurance pool, and deposits 1e18 shares.
  2. seizeBadDebt is called with 2e18. Now, there are pendingObligations = 1e18, and there is 0 vusd in the insurance fund.
  3. Bob (the attacker) directly transfers 1e18 + 1 vUSD.
  4. Bob calls deposit with 1e18 vUSD. All pending obligations will be settled, but there will only be 1 vUSD left in the pool before Bob's deposit. Bob receives shares = 1e18 * 1e18 / 1. As a result, Bob will get 1e36 shares, diluting Alice's share of the pool. Bob will be able to take a much larger share of all future profits from the insurance fund until more bad debt is seized. Bob only provided 2e18 + 1 liqudiity, but received an exponentially larger number of shares than Alice.

Mitigation

it depends on how you want this to work. You could keep track of the total amount ever contributed by users, and use that for calculations. Or just make staking 1 vUSD = 1 share if the pool total is below the total number of shares.

atvanguard commented 2 years ago

We are still evaluating this. It might be changed to sponsor disputed

atvanguard commented 2 years ago

Disputing this. It is by design. LPs who were in the insurance fund will be burnt during a bad debt settlement.