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Regnum Aurum Acquisition Corp
HardhatReal World AssetsNFT
77,280 USDC
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Submission Details
Severity: medium
Invalid

M-3 Users Do Not Pay Interest Balance When Minting RToken Again After Initial Mint in `RToken::mint`

0x996

Description

In the mint function, the purpose of balanceIncrease is to calculate the user's balance increase due to changes in the liquidity index. This is because the balance of RToken increases over time as interest accumulates.

However, in RToken::mint, it is not used, so after the user mints RToken for the first time, they do not pay the interest balance when minting again, resulting in an incorrect total minted amount.

Note:

  1. The DebtToken::burn function has a similar issue!

    1. Suggested fix: Add uint256 amountToburn = amount + borrowIndex;, then _burn(from, amountToburn.toUint128());

Impact

Total Minted Amount Calculation: The original minted amount (amountToMint) should be added to the calculated balance increase (balanceIncrease) to determine the actual total amount to mint. Currently, since balanceIncrease is not used, users do not pay the interest balance (balanceIncrease) when minting RToken again after the first mint.

Recommendations

function mint(
address caller,
address onBehalfOf,
uint256 amountToMint,
uint256 index
) external override onlyReservePool returns (bool, uint256, uint256, uint256) {
if (amountToMint == 0) {
return (false, 0, 0, 0);
}
uint256 amountScaled = amountToMint.rayDiv(index);
if (amountScaled == 0) revert InvalidAmount();
​
uint256 scaledBalance = balanceOf(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);
}
​
_userState[onBehalfOf].index = index.toUint128();
- _mint(onBehalfOf, amountToMint.toUint128());
+ uint256 amount = amountToMint + balanceIncrease;
+ _mint(onBehalfOf, amount.toUint128());
​
emit Mint(caller, onBehalfOf, amountToMint, index);
​
return (isFirstMint, amountToMint, totalSupply(), amountScaled);
}
Updates

Lead Judging Commences

inallhonesty Lead Judge 7 months ago
Submission Judgement Published
Invalidated
Reason: Incorrect statement
Assigned finding tags:

DebtToken::burn calculates balanceIncrease (interest) but never applies it, allowing borrowers to repay loans without paying accrued interest

Interest IS applied through the balanceOf() mechanism. The separate balanceIncrease calculation is redundant/wrong. Users pay full debt including interest via userBalance capping.

RToken::mint calculates balanceIncrease (interest accrued since last interaction) but never mints it, causing users to lose earned interest between deposits

The balanceIncrease is the interest that has already accrued on the user's existing scaledBalance since their last interaction. It's not something you mint as new tokens in the _mint function.

inallhonesty Lead Judge 7 months ago
Submission Judgement Published
Invalidated
Reason: Incorrect statement
Assigned finding tags:

DebtToken::burn calculates balanceIncrease (interest) but never applies it, allowing borrowers to repay loans without paying accrued interest

Interest IS applied through the balanceOf() mechanism. The separate balanceIncrease calculation is redundant/wrong. Users pay full debt including interest via userBalance capping.

RToken::mint calculates balanceIncrease (interest accrued since last interaction) but never mints it, causing users to lose earned interest between deposits

The balanceIncrease is the interest that has already accrued on the user's existing scaledBalance since their last interaction. It's not something you mint as new tokens in the _mint function.

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