Storage Proofs

Summary

The ScrvusdVerifierV1 contract incorrectly calculates the storage slot for the balanceOf mapping, causing it to read from the wrong location in the scrvUSD contract's storage. This results in the oracle using an incorrect (likely zero) value for balance_of_self, which affects price calculations.

Vulnerability Details

In Ethereum's storage layout, the correct way to calculate a storage slot for a mapping at position p with key k is:

However, in ScrvusdVerifierV1, the contract reverses this order when calculating the slot for balanceOf:

The comment indicates that slot 18 is the balanceOf mapping and SCRVUSD is the address whose balance we want to read. The correct calculation should be:

Since the parameters are reversed in the calculation, the verifier will read from an entirely different storage slot than intended. This slot is likely to contain zero or some unrelated value.

Impact

This vulnerability impacts the accuracy of price calculations in the oracle system:

The balance_of_self parameter is used in several critical calculations:

• In _obtain_price_params to calculate gain:

• In _unlocked_shares to determine unlocked shares when all profits are unlocked:

2. These calculations directly influence the price of scrvUSD on the target chain.

3. Using an incorrect (likely zero) balance_of_self value would:

• Underestimate the calculated gain per period

• Incorrectly report unlocked shares

• Eventually lead to undercalculation of the scrvUSD price
  This results in a lower-than-actual price for scrvUSD on the target chain, potentially allowing users to buy scrvUSD at a discount compared to its true value.

Tools Used

Manual code review

Recommendations

Correct the storage slot calculation by reversing the parameter order: