[mertcano]

Summary of Changes

Addresses Critical, High, and Medium findings from the workspace security audit in stablecoin-evm[cite: 27, 32, 37]:

1. Migration Initializer Access Control (FiatTokenV2, FiatTokenV2_1, FiatTokenV2_2 - Critical): Added onlyOwner access control, zero-address validation, and strict version monotonicity checks to prevent unauthorized re-initialization, balance sweeping, and EIP-712 domain corruption[cite: 32, 59, 60, 61].
2. Native-Fiat Blocklist Modifier Enforcement (NativeFiatTokenV2_2 - High): Restored notBlacklisted modifiers across transfer, transferFrom, and all authorization overloads ((v, r, s) and (bytes signature)), closing blocklist bypass vectors[cite: 32, 62].
3. Celo Fee Caller Zero-Address Guard (FiatTokenCeloV2_2 - Medium): Restricted updateFeeCaller against address(0) to protect the Celo gas lifecycle and added FeeCallerChanged event emission for auditability[cite: 37, 58].
4. UpgradeabilityProxy Architectural Documentation (Reviewed & Dismissed): Added explicit architectural notes recording why transparent proxies omit on-chain proxiableUUID() checks[cite: 44, 63].

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Vulnerability Analysis

• Unprotected Initializers (Critical - Cat 2):

  • initializeV2, initializeV2_1, and initializeV2_2 relied strictly on _initializedVersion without caller authorization[cite: 32].
  • Following proxy upgrade, an attacker could call initializeV2_1 to drain contract-held USDC to an arbitrary lostAndFound address, or invoke initializeV2_2 to modify the token symbol (corrupting EIP-712 domain separators) and freeze victim accounts[cite: 32].

• Dropped Blocklist Modifiers (High - Cat 14):

  • Overrides in NativeFiatTokenV2_2 dropped parent notBlacklisted modifiers, allowing blocklisted accounts to transfer native-fiat tokens directly or through signed authorizations[cite: 32].

• Zero-Address Fee Caller (Medium - Cat 8):

  • Passing address(0) to updateFeeCaller permanently broke debitGasFees/creditGasFees, bricking gas fee payments for Celo transactions[cite: 37, 58].

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Key Remediations

• contracts/v2/FiatTokenV2.sol:
  • Added onlyOwner and require(initialized && _initializedVersion == 0, ...) to initializeV2[cite: 59].
• contracts/v2/FiatTokenV2_1.sol:
  • Added onlyOwner, require(_initializedVersion == 1, ...), and require(lostAndFound != address(0), ...) to initializeV2_1[cite: 60].
• contracts/v2/FiatTokenV2_2.sol:
  • Added onlyOwner and require(_initializedVersion == 2, ...) to initializeV2_2[cite: 61].
• contracts/v2/NativeFiatTokenV2_2.sol:
  • Restored notBlacklisted(msg.sender) notBlacklisted(to) on transfer.
  • Restored notBlacklisted(from) notBlacklisted(to) on transferFrom and all transferWithAuthorization / receiveWithAuthorization variants[cite: 62].
• contracts/v2/celo/FiatTokenCeloV2_2.sol:
  • Added require(_newFeeCaller != address(0), "FiatTokenCeloV2_2: zero fee caller") and emitted FeeCallerChanged(_newFeeCaller).

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Verification

• Compiled with pinned solc 0.6.12 via standard-JSON: 0 errors, 0 warnings across all 7 targets (FiatTokenV2, V2_1, V2_2, NativeFiatTokenV2_2, FiatTokenCeloV2_2, FiatTokenV1, FiatTokenProxy).