Part 2

1. Summary

The load() function incorrectly computes storage slots for vaults using keccak256(abi.encode(VAULT_LOCATION, vaultId)), reversing the standard Solidity mapping slot order. This violates Solidity’s storage layout rules, creating risks of key collision and data corruption where multiple vaults/mappings could overwrite each other’s storage slots.

2. Vulnerability Details

Faulty Code

Technical Breakdown

1. Solidity Storage Rules:
   For mappings and dynamic storage, slots are calculated as:

   slot = keccak256(abi.encode(key, base_slot))

   • key: Unique identifier (e.g., vaultId)

   • base_slot: Precomputed namespace (e.g., VAULT_LOCATION)

2. Incorrect Implementation:
   The code reverses the order:

   slot = keccak256(abi.encode(VAULT_LOCATION, vaultId)) // (base_slot, key)

   This causes:

   • All vaults to share a linear sequence of slots starting from keccak256(VAULT_LOCATION)

   • High probability of slot collisions between vaults with sequential IDs

3. Collision Example:
   For VAULT_LOCATION = 0x123... and vaultId = 1:

   • Correct Slot: keccak256(abi.encode(1, 0x123...))

   • Actual Slot: keccak256(abi.encode(0x123..., 1))
     These produce entirely different (and non-isolated) storage locations.

3. Impact

• Mapping Overlap: Other mappings using keccak256(key, base_slot) could overwrite vault data
• Protocol-Wide Instability: Financial accounting errors in debt/collateral tracking
• Exploit Potential: Attackers could deliberately collide slots to manipulate balances

Example Scenario:

1. Vault #1 uses slot keccak256(VAULT_LOCATION || 1)

2. Another mapping uses slot keccak256(1 || OTHER_BASE_SLOT)

3. If VAULT_LOCATION = OTHER_BASE_SLOT, these slots collide, causing silent data overwrites.

4. Recommendations

Immediate Fix

Correct the slot calculation order:

Preventative Measures

1. Storage Layout Tests:
   Add Foundry tests to verify slot isolation:

   function test_SlotIsolation() public {

   uint128 vaultA = 1;

   uint128 vaultB = 2;

   bytes32 slotA = keccak256(abi.encode(vaultA, VAULT_LOCATION));

   bytes32 slotB = keccak256(abi.encode(vaultB, VAULT_LOCATION));

   // Ensure slots are non-sequential and isolated

   assertTrue(uint256(slotB) - uint256(slotA) > 1);

   }

2. Static Analysis Rule:
   Implement a Slither custom detector to flag reversed abi.encode orders in keccak256 calls:

   detectors:

   - name: "reversed-slot-order"

   description: "Detect keccak256(abi.encode(base_slot, key)) patterns"

   regex: "keccak256\(abi\.encode\(.*,\s*.*key.*\)\)"

3. Documentation Update:
   Explicitly document storage slot conventions in the codebase:

   "For namespaced storage, always use keccak256(abi.encode(key, base_slot))."