Accrued Interest Is Lost When Minting Due to Missing balanceIncrease Adjustment in `RToken` contract
Summary
The _mint() function in RToken contract, does not account for balanceIncrease, causing accrued interest to be lost when updating _userState[onBehalfOf].index.
Vulnerability Details
In the mint() function, the accrued interest (balanceIncrease) is calculated as:
However, balanceIncrease is not added to amountToMint when calling _mint():
Since _userState[onBehalfOf].index is updated right after:
This means that any previously accrued interest (balanceIncrease) is effectively reset and lost, leading to incorrect interest calculations for users.
Impact
Users will lose the interest accrued before the current minting transaction, leading to an underestimation of their balance and overall yield loss.
Tools Used
Manual Review
Recommendations
Update _mint() to include balanceIncrease, ensuring users receive their full entitled interest before resetting _userState[onBehalfOf].index.
Lead Judging Commences
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.
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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