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

Incorrect Burn Amount in the `RToken.burn()` Function

kupiasec

Summary

The RToken.burn() function burns an amount using amount instead of a scaled amount. Here, amount represents the quantity of reserve tokens being withdrawn, and burning RToken at this value implies an exchange rate of 1:1. This is incorrect.

Vulnerability Details

The RToken.burn() function burns an amount using amount.

Since amount represents the amount of reserve tokens being withdrawn, burning RToken at this value means that the exchange rate is 1:1, which is incorrect.

Instead, the burn amount should be a scaled value according to the exchange rate index.

As a result, the withdrawer burns more RTokens than they should.

function burn(
address from,
address receiverOfUnderlying,
uint256 amount,
uint256 index
) external override onlyReservePool returns (uint256, uint256, uint256) {
if (amount == 0) {
return (0, totalSupply(), 0);
}
​
uint256 userBalance = balanceOf(from);
​
_userState[from].index = index.toUint128();
​
if(amount > userBalance){
amount = userBalance;
}
​
uint256 amountScaled = amount.rayMul(index);
​
_userState[from].index = index.toUint128();
​
176 _burn(from, amount.toUint128());
​
if (receiverOfUnderlying != address(this)) {
IERC20(_assetAddress).safeTransfer(receiverOfUnderlying, amount);
}
​
emit Burn(from, receiverOfUnderlying, amount, index);
​
return (amount, totalSupply(), amount);
}

Impact

Withdrawers burn more RTokens than they should.

Tools Used

Manual review

Recommendations

The burn amount should be scaled.

function burn(
address from,
address receiverOfUnderlying,
uint256 amount,
uint256 index
) external override onlyReservePool returns (uint256, uint256, uint256) {
if (amount == 0) {
return (0, totalSupply(), 0);
}
​
uint256 userBalance = balanceOf(from);
​
_userState[from].index = index.toUint128();
​
if(amount > userBalance){
amount = userBalance;
}
​
uint256 amountScaled = amount.rayMul(index);
​
_userState[from].index = index.toUint128();
​
- _burn(from, amount.toUint128());
+ _burn(from, amount.rayDiv(index).toUint128());
​
if (receiverOfUnderlying != address(this)) {
IERC20(_assetAddress).safeTransfer(receiverOfUnderlying, amount);
}
​
emit Burn(from, receiverOfUnderlying, amount, index);
​
- return (amount, totalSupply(), amount);
+ return (amount.rayDiv(index), totalSupply(), amount);
}
Updates

Lead Judging Commences

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

RToken::burn returns incorrect underlying asset amount (amount instead of amountScaled), leading to wrong interest rate calculations

RToken::burn incorrectly burns amount (asset units) instead of amountScaled (token units), breaking token economics and interest-accrual mechanism

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

RToken::burn returns incorrect underlying asset amount (amount instead of amountScaled), leading to wrong interest rate calculations

RToken::burn incorrectly burns amount (asset units) instead of amountScaled (token units), breaking token economics and interest-accrual mechanism

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