Submission Details
Severity:
debtToken incorrectly scales indexes
Within debtToken balance of accounts are scaled to normalize debt usage index. This is used to determine the balanceIncrease to be added to the minted debt position.
https://github.com/Cyfrin/2025-02-raac/blob/main/contracts/core/tokens/DebtToken.sol#L150
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);
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();
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());
}
function burn(
address from,
uint256 amount,
uint256 index
) external override onlyReservePool returns (uint256, uint256, uint256, uint256) {
if (from == address(0)) revert InvalidAddress();
if (amount == 0) {
return (0, totalSupply(), 0, 0);
}
uint256 userBalance = balanceOf(from);
uint256 balanceIncrease = 0;
if (_userState[from].index != 0 && _userState[from].index < index) {
uint256 borrowIndex = ILendingPool(_reservePool).getNormalizedDebt();
@> balanceIncrease = userBalance.rayMul(borrowIndex) - userBalance.rayMul(_userState[from].index);
amount = amount;
}
_userState[from].index = index.toUint128();
if(amount > userBalance){
amount = userBalance;
}
uint256 amountScaled = amount.rayDiv(index);
if (amountScaled == 0) revert InvalidAmount();
_burn(from, amount.toUint128());
emit Burn(from, amountScaled, index);
return (amount, totalSupply(), amountScaled, balanceIncrease);
}
function balanceOf(address account) public view override(ERC20, IERC20) returns (uint256) {
uint256 scaledBalance = super.balanceOf(account);
return scaledBalance.rayMul(ILendingPool(_reservePool).getNormalizedDebt());//@audit-info already scaled through rayMul
}
The issue is that when determining scaledbalance that would be used to determine the balanceIncreasewithin mint it uses balanceOf which has already been scaled by the debt index also within the burn function.
Impact
Incorrect scaling result to erroneous calculation and loss of funds
Recommendation
function burn(
address from,
uint256 amount,
uint256 index
) external override onlyReservePool returns (uint256, uint256, uint256, uint256) {
if (from == address(0)) revert InvalidAddress();
if (amount == 0) {
return (0, totalSupply(), 0, 0);
}
uint256 userBalance = balanceOf(from);
+ uint256 scaledBalance = scaledBalanceOf(from);
uint256 balanceIncrease = 0;
if (_userState[from].index != 0 && _userState[from].index < index) {
uint256 borrowIndex = ILendingPool(_reservePool).getNormalizedDebt();
- balanceIncrease = userBalance.rayMul(borrowIndex) - userBalance.rayMul(_userState[from].index);
+ balanceIncrease = scaledBalance.rayMul(borrowIndex) - scaledBalance.rayMul(_userState[from].index);
- amount = amount;
+ amount = amount + balanceIncrease;
}
_userState[from].index = index.toUint128();
if(amount > userBalance){
amount = userBalance;
}
uint256 amountScaled = amount.rayDiv(index);
if (amountScaled == 0) revert InvalidAmount();
_burn(from, amount.toUint128());
emit Burn(from, amountScaled, index);
return (amount, totalSupply(), amountScaled, balanceIncrease);
}
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);
}
_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());
}
Updates
Lead Judging Commences
inallhonesty 7 months ago
Submission Judgement Published Assigned finding tags:
DebtToken::mint miscalculates debt by applying interest twice, inflating borrow amounts and risking premature liquidations
Prize pool breakdown
Total prize
77,280 USDC
nSLOC
3,86420
USDC / LOC
74,000
3,280
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