Miscalculation of `_supplyCreditUni` allows undercollateralized loan

[code423n4]

Handle

WatchPug

Vulnerability details

https://github.com/code-423n4/2021-09-wildcredit/blob/c48235289a25b2134bb16530185483e8c85507f8/contracts/LendingPair.sol#L660-L684

In _supplyCreditUni(), the calculation of the collateral value of tokenB supply is using _priceB instead of _priceA, which can lead to undercollateralized loans.

  function _supplyCreditUni(
    address _account,
    address _returnToken,
    uint    _priceA,
    uint    _priceB,
    uint    _colFactorA,
    uint    _colFactorB
  ) internal view returns(uint) {

    if (uniPosition[_account] > 0) {

      (uint amountA, uint amountB) = uniV3Helper.positionAmounts(uniPosition[_account], _priceA, _priceB);

      uint supplyA = _convertTokenValues(tokenA, _returnToken, amountA, _priceA, _priceB);
      uint supplyB = _convertTokenValues(tokenB, _returnToken, amountB, _priceB, _priceB);

      uint creditA = supplyA * _colFactorA / 100e18;
      uint creditB = supplyB * _colFactorB / 100e18;

      return (creditA + creditB);

    } else {
      return 0;
    }
  }

Impact

Undercollateralized debts cannot be liquidated and it leads to bad debts to the protocol.

An attacker can deposit a small sum of collateral asset and borrow a rather large amount of asset, essentially steal funds from the protocol.

Proof of Concept

Given:

• tokenA is BTC, tokenB is USDC;
• Price of BTC is 5000 USDC;
• The collateral factor is 80%.

An attacker can:

1. Deposit a Uni v3 position of 0 BTC and 500 USDC;
2. The miscalculation made the protocol believes that the attacker has 500 BTC worth of collateral;
3. Borrow 400 BTC.

The attacker steals ~399.9 BTC from the protocol.

Recommendation

Consider changing to:

uint supplyB = _convertTokenValues(tokenB, _returnToken, amountB, _priceB, _priceA);

[talegift]

Duplicate #70