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Submission Details
Severity: medium
Invalid

Erroneous double hashing of the mapping slot (such as balanceOf(self))

libaier1997

Summary

The contract ScrvusdVerifierV1 contains an error in computing storage slot hashes for mapping-type slots in the _extractParametersFromProof function. Specifically, the storage position for mapping-type slots (e.g., balanceOf(address)) has already been correctly computed in the storage definition, yet the extractSlotValueFromProof function call incorrectly performs an extra hashing operation, causing an incorrect slot position computation:

/// @dev Extract parameters from the state proof using the given state root.
function _extractParametersFromProof(
bytes32 stateRoot,// blockNumber
bytes memory proofRlp
) internal view returns (uint256[PARAM_CNT] memory) {
........
// Extract slot values
uint256[PARAM_CNT] memory params;
for (uint256 i = 1; i < PROOF_CNT; i++) {
Verifier.SlotValue memory slot = Verifier.extractSlotValueFromProof(
keccak256(abi.encode(PARAM_SLOTS[i])),//<-@ extra hashing operation
account.storageRoot,
proofs[i].toList()
);
// Slots might not exist, but typically we just read them.
params[i - 1] = slot.value;
}
​
return params;
}

For the mapping slots, the position was already pre-hashed correctly:

// Storage slots of parameters
uint256[PROOF_CNT] internal PARAM_SLOTS = [
uint256(0), // filler for account proof
uint256(21), // total_debt
uint256(22), // total_idle
uint256(20), // totalSupply
uint256(38), // full_profit_unlock_date
uint256(39), // profit_unlocking_rate
uint256(40), // last_profit_update
uint256(keccak256(abi.encode(18, SCRVUSD))) // <-@ For the mapping slots, the position was already pre-hashed correctly
];

Applying an additional hash is incorrect and it creates an inconsistency with the expected behavior.

Vulnerability Details

Root Cause：The contract does not differentiate clearly between static and mapping slots. Although static slots must be hashed once during verification, the mapping-type slots have been hashed correctly beforehand and must not be hashed again. The incorrect additional hashing of the mapping slot leads to an incorrect storage slot calculation, resulting in a failure to verify the state proof properly.

Impact

This vulnerability causes the contract to incorrectly verify or fail to verify real data stored in mapping slots (balanceOf(self)).

Tools Used

N/A

Recommendations

  1. Explicitly distinguish between static and mapping storage slots by modifying the verification logic to correctly handle hashing

Updates

Lead Judging Commences

0xnevi Lead Judge
3 months ago
0xnevi Lead Judge 3 months ago
Submission Judgement Published
Invalidated
Reason: Incorrect statement
Assigned finding tags:

[invalid] finding-storage-key-compute-wrong

See primary comments in issue #23

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