Summary

• Incorrect storage slot mapping between the Vyper-based scrvUSD oracle and the Solidity verifier contract.

• This mismatch causes the verifier to read incorrect data from storage, leading to corrupted price calculations.

Vulnerability Details

The Vyper contract (scrvUSD oracle) assigns storage slots sequentially to its variables:

The Solidity verifier (ScrvusdVerifierV1) incorrectly assumes slots for price_params start at Slot 21 instead of Slot 6:

total\_debt is read from Slot 21 (actual: Slot 6).

balance\_of\_self uses keccak256 (wrong; Vyper stores it at Slot 12 directly)

Vyper Storage Layout:

Variable | Slot
last_block_number - 0
last_prices[0] - 1
price_params.total_debt - 6
price_params.balance_of_self- 12

Solidity’s Incorrect Slots:

Parameter | Slot Used | Actual Slot
total_debt | 21 | 6
total_idle | 22 | 7
balance_of_self | keccak(...) | 12\

This mismatch causes the verifier to read unrelated data (e.g., other variables or empty slots), leading to garbage values.

Impact

• Corrupted Price Data: Reading incorrect data, the prices it reports will be wrong and unreliable.

• Broken Integrations: If the oracle is feeding bad data, these integrations will malfunction or break down.

Tools Used

Manual Code Review.

Vyper Storage Analysis.

Recommendations

Update PARAM_SLOTS in ScrvusdVerifierV1 to match Vyper’s actual slots.