Storage Proofs

Summary

The contract incorrectly calculates the storage slot for the balanceOf(self) mapping by reversing the order of the key and base slot in the abi.encode function. It also mishandles simple storage variables by hashing their slot numbers unnecessarily. As a result, the contract reads from incorrect storage locations, leading to invalid parameter values that undermine the oracle’s reliability.

Vulnerability Details

https://github.com/CodeHawks-Contests/2025-03-curve/blob/198820f0c30d5080f75073243677ff716429dbfd/contracts/scrvusd/verifiers/ScrvusdVerifierV1.sol#L40C9-L40C71

Affected Component : The PARAM_SLOTS array, specifically the entry for balanceOf(self), and the _extractParametersFromProof function that processes state proofs.

Root Cause:
For balanceOf(self), the slot is calculated as keccak256(abi.encode(18, SCRVUSD)) instead of the correct keccak256(abi.encode(SCRVUSD, 18)).
For simple variables (e.g., total_debt), the slot is hashed (e.g., keccak256(abi.encode(21))) rather than passed directly as 21.

Technical Impact:
The contract retrieves invalid data for balanceOf(self) and potentially other parameters due to accessing incorrect storage slots.
This breaks the functionality of the verifyScrvusdByBlockHash and verifyScrvusdByStateRoot functions, which rely on accurate parameter extraction to update the scrvUSD oracle .

Impact

The incorrect storage slot calculation directly impairs the contract’s core purpose: verifying and updating the scrvUSD oracle with accurate data. Invalid parameter values can lead to:
Incorrect price calculations in the oracle.
Financial losses or miscalculations in systems relying on the oracle.
Erosion of trust in the oracle’s accuracy.
The issue affects all transactions invoking verifyScrvusdByBlockHash or verifyScrvusdByStateRoot, making it a systemic flaw with widespread consequences.
Scope: Impacts the entire oracle update process, affecting downstream applications and users dependent on the scrvUSD oracle.

Tools Used

Manual code review

Recommendations

Correct Mapping Slot Calculation :
Update the balanceOf(self) slot calculation in the PARAM_SLOTS array to :