Delightful Syrup Scorpion - Double Debond Fee Application in _calculateBasePerPTkn()

[sherlock-admin3]

Delightful Syrup Scorpion

High

Double Debond Fee Application in _calculateBasePerPTkn()

Summary

The debond fee is applied twice when calculating _spTknBasePrice18 in the spTknMinimalOracle contract. This causes mispricing of spTkn which is used as collateral in the fraxlend pairs, causing unfair liquidations.

Root Cause

in the spTknMinimalOracle, when getPrices() is called, the _calculateBasePerPTkn function makes two adjustements if BASE_IS_POD. One for the pod CBR, and one for the unwrap fee:

    function _checkAndHandleBaseTokenPodConfig(uint256 _currentPrice18) internal view returns (uint256 _finalPrice18) {
        _finalPrice18 = _accountForCBRInPrice(BASE_TOKEN, address(0), _currentPrice18);
        _finalPrice18 = _accountForUnwrapFeeInPrice(BASE_TOKEN, _finalPrice18);
    }

https://github.com/sherlock-audit/2025-01-peapods-finance/blob/d28eb19f4b39d3db7997477460f9f9c76839cb0c/contracts/contracts/oracle/spTKNMinimalOracle.sol#L213-L216

But when accounting for the CBR, it uses .convertToAssets() on the pod, which already accounts for the unwrap/debond fee:
https://github.com/sherlock-audit/2025-01-peapods-finance/blob/d28eb19f4b39d3db7997477460f9f9c76839cb0c/contracts/contracts/WeightedIndex.sol#L128
So the debond fee is incorrectly applied twice when pricing the spTkn in the oracle.

Internal Pre-conditions

Base token is a pod token

External Pre-conditions

None

Attack Path

None

Impact

spTkn token price is undervalued

Since it is used as collateral in lending pairs, borrowers in the FraxLend pair will be unfairly liquidated.

PoC

No response

Mitigation

Dont apply the debond fee twice