Core Contracts
Regnum Aurum Acquisition Corp
HardhatReal World AssetsNFT
77,280 USDC
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Submission Details
Severity: high
Valid

Incorrect balance calculation in `DebtToken.sol` will cause inflated debt positions for users due to double scaling of balances during the mint operation.

rampage

Root Cause

In DebtToken.sol the mint() function incorrectly uses balanceOf() instead of scaledBalanceOf() when calculating balance increases, leading to double scaling of balances.

Impact

Users will have incorrectly calculated debt positions due to the double scaling issue. This impacts both:

  1. The recorded debt amount (amountToMint)

  2. The emitted events with wrong balanceIncrease values

Technical Details

The vulnerability exists in the mint() function where:

  1. scaledBalance is fetched using balanceOf() which returns an already scaled value

  2. This scaled value is then scaled again in the balanceIncrease calculation:

function mint(
address user,
address onBehalfOf,
uint256 amount,
uint256 index
) external override onlyReservePool returns (bool, uint256, uint256) {
if (user == address(0) || onBehalfOf == address(0)) revert InvalidAddress();
if (amount == 0) {
return (false, 0, totalSupply());
}
​
uint256 amountScaled = amount.rayDiv(index);
if (amountScaled == 0) revert InvalidAmount();
​
150-> uint256 scaledBalance = balanceOf(onBehalfOf);
bool isFirstMint = scaledBalance == 0;
​
uint256 balanceIncrease = 0;
if (_userState[onBehalfOf].index != 0 && _userState[onBehalfOf].index < index) {
155-> balanceIncrease = scaledBalance.rayMul(index) - scaledBalance.rayMul(_userState[onBehalfOf].index);
}
​
_userState[onBehalfOf].index = index.toUint128();
​
-> uint256 amountToMint = amount + balanceIncrease;
​
_mint(onBehalfOf, amountToMint.toUint128());
​
emit Transfer(address(0), onBehalfOf, amountToMint);
-> emit Mint(user, onBehalfOf, amountToMint, balanceIncrease, index);
​
return (scaledBalance == 0, amountToMint, totalSupply());
}

Mitigation

Replace balanceOf() with scaledBalanceOf() to prevent double scaling of balances:

function mint(
address user,
address onBehalfOf,
uint256 amount,
uint256 index
) external override onlyReservePool returns (bool, uint256, uint256) {
if (user == address(0) || onBehalfOf == address(0)) revert InvalidAddress();
if (amount == 0) {
return (false, 0, totalSupply());
}
​
uint256 amountScaled = amount.rayDiv(index);
if (amountScaled == 0) revert InvalidAmount();
​
- uint256 scaledBalance = balanceOf(onBehalfOf);
+ uint256 scaledBalance = scaledBalanceOf(onBehalfOf);
bool isFirstMint = scaledBalance == 0;
uint256 balanceIncrease = 0;
if (_userState[onBehalfOf].index != 0 && _userState[onBehalfOf].index < index) {
balanceIncrease = scaledBalance.rayMul(index) - scaledBalance.rayMul(_userState[onBehalfOf].index);
}
.........................
​
return (scaledBalance == 0, amountToMint, totalSupply());
}
Updates

Lead Judging Commences

inallhonesty Lead Judge 7 months ago
Submission Judgement Published
Validated
Assigned finding tags:

DebtToken::mint miscalculates debt by applying interest twice, inflating borrow amounts and risking premature liquidations

inallhonesty Lead Judge 7 months ago
Submission Judgement Published
Validated
Assigned finding tags:

DebtToken::mint miscalculates debt by applying interest twice, inflating borrow amounts and risking premature liquidations

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