Volt Protocol contest - defsec's results

C4-001 : Incompatibility With Rebasing/Deflationary/Inflationary tokens

Impact - LOW

PrePo protocol do not appear to support rebasing/deflationary/inflationary tokens whose balance changes during transfers or over time. The necessary checks include at least verifying the amount of tokens transferred to contracts before and after the actual transfer to infer any fees/interest.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/pcv/PCVDeposit.sol#L30
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L206
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L293
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L242
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L280

Tools Used

Manual Code Review

Recommended Mitigation Steps

• Ensure that to check previous balance/after balance equals to amount for any rebasing/inflation/deflation
• Add support in contracts for such tokens before accepting user-supplied tokens
• Consider supporting deflationary / rebasing / etc tokens by extra checking the balances before/after or strictly inform your users not to use such tokens if they don't want to lose them.

C4-002 : Missing zero-address check in constructors and the setter functions

Impact - LOW

Missing checks for zero-addresses may lead to infunctional protocol, if the variable addresses are updated incorrectly.

Proof of Concept

1. Navigate to the following all contract functions.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L85

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/pcv/compound/ERC20CompoundPCVDeposit.sol#L22

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/pcv/compound/CompoundPCVDepositBase.sol#L31

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/oracle/ScalingPriceOracle.sol#L71

Tools Used

Code Review

Recommended Mitigation Steps

Consider adding zero-address checks in the discussed constructors: require(newAddr != address(0));.

C4-003 : transferOwnership should be two step process

Impact - LOW

The current ownership transfer process involves the current owner calling Unlock.transferOwnership(). This function checks the new owner is not the zero address and proceeds to write the new owner's address into the owner's state variable. If the nominated EOA account is not a valid account, it is entirely possible the owner may accidentally transfer ownership to an uncontrolled account, breaking all functions with the onlyOwner() modifier. Lack of two-step procedure for critical operations leaves them error-prone if the address is incorrect, the new address will take on the functionality of the new role immediately

for Ex : -Alice deploys a new version of the whitehack group address. When she invokes the whitehack group address setter to replace the address, she accidentally enters the wrong address. The new address now has access to the role immediately and is too late to revert

Proof of Concept

1. https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/oracle/OraclePassThrough.sol#L14.
2. The contracts have many onlyOwner function.
3. The contract is inherited from the Ownable which includes transferOwnership.

Tools Used

None

Recommended Mitigation Steps

Implement zero address check and Consider implementing a two step process where the owner nominates an account and the nominated account needs to call an acceptOwnership() function for the transfer of ownership to fully succeed. This ensures the nominated EOA account is a valid and active account.

C4-004 : Consider making contracts Pausable

Impact - LOW

There are many external risks so my suggestion is that you should consider making the contracts pausable, so in case of an unexpected event, the admin can pause transfers.

Tools Used

Code Review

Recommended Mitigation Steps

Consider making contracts Pausable https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/security/Pausable.sol.

C4-005 : Critical changes should use two-step procedure

Impact - NON CRITICAL

The critical procedures should be two step process.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L157
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L167
https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/peg/NonCustodialPSM.sol#L182

Tools Used

Code Review

Recommended Mitigation Steps

Lack of two-step procedure for critical operations leaves them error-prone. Consider adding two step procedure on the critical functions.

C4-006 : Front-runnable Initializers

Impact - LOW

All contract initializers were missing access controls, allowing any user to initialize the contract. By front-running the contract deployers to initialize the contract, the incorrect parameters may be supplied, leaving the contract needing to be redeployed.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Core.sol#L20

2. initialize functions does not have access control. They are vulnerable to front-running.

Tools Used

Manual Code Review

Recommended Mitigation Steps

While the code that can be run in contract constructors is limited, setting the owner in the contract's constructor to the msg.sender and adding the onlyOwner modifier to all initializers would be a sufficient level of access control.

C4-007 : Missing events for only functions that change critical parameters

Impact - Non critical

The afunctions that change critical parameters should emit events. Events allow capturing the changed parameters so that off-chain tools/interfaces can register such changes with timelocks that allow users to evaluate them and consider if they would like to engage/exit based on how they perceive the changes as affecting the trustworthiness of the protocol or profitability of the implemented financial services. The alternative of directly querying on-chain contract state for such changes is not considered practical for most users/usages.

Missing events and timelocks do not promote transparency and if such changes immediately affect users’ perception of fairness or trustworthiness, they could exit the protocol causing a reduction in liquidity which could negatively impact protocol TVL and reputation.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/oracle/ScalingPriceOracle.sol#L218

See similar High-severity H03 finding OpenZeppelin’s Audit of Audius (https://blog.openzeppelin.com/audius-contracts-audit/#high) and Medium-severity M01 finding OpenZeppelin’s Audit of UMA Phase 4 (https://blog.openzeppelin.com/uma-audit-phase-4/)

Tools Used

None

Recommended Mitigation Steps

Add events to all functions that change critical parameters.

C4-008 : Upgrade Pragma To solidity 0.8.10+

Impact

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

Proof of Concept

Solidity 0.8.10 has a useful change which reduced gas costs of external calls which expect a return value: https://blog.soliditylang.org/2021/11/09/solidity-0.8.10-release-announcement/

Code Generator: Skip existence check for external contract if return data is expected. In this case, the ABI decoder will revert if the contract does not exist

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.10.

C4-001: Revert String Size Optimization

Impact

Shortening revert strings to fit in 32 bytes will decrease deploy time gas and will decrease runtime gas when the revert condition has been met.

Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Proof of Concept

Revert strings > 32 bytes are here:

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/oracle/ScalingPriceOracle.sol#L140

  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/CoreRef.sol::48 => "CoreRef: Caller is not a PCV controller"
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/CoreRef.sol::56 => "CoreRef: Caller is not a governor or contract admin"
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/CoreRef.sol::64 => "CoreRef: Caller is not a governor"
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/CoreRef.sol::72 => "CoreRef: Caller is not a guardian or governor"
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/CoreRef.sol::82 => "CoreRef: Caller is not governor or guardian or admin"

Tools Used

Manual Review

Recommended Mitigation Steps

Shorten the revert strings to fit in 32 bytes. That will affect gas optimization.

C4-002 : Adding unchecked directive can save gas

Impact

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

Proof of Concept

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/volt/Volt.sol#L83

Tools Used

None

Recommended Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible.

C4-003 : Free gas savings for using solidity 0.8.10+

Impact

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

Proof of Concept

Solidity 0.8.10 has a useful change which reduced gas costs of external calls which expect a return value: https://blog.soliditylang.org/2021/11/09/solidity-0.8.10-release-announcement/

Code Generator: Skip existence check for external contract if return data is expected. In this case, the ABI decoder will revert if the contract does not exist

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.10.

C4-004 : Use calldata instead of memory for function parameters

Impact

In some cases, having function arguments in calldata instead of memory is more optimal.

Consider the following generic example:

contract C {
function add(uint[] memory arr) external returns (uint sum) {
uint length = arr.length;
for (uint i = 0; i < arr.length; i++) {
sum += arr[i];
}
}
}

In the above example, the dynamic array arr has the storage location memory. When the function gets called externally, the array values are kept in calldata and copied to memory during ABI decoding (using the opcode calldataload and mstore). And during the for loop, arr[i] accesses the value in memory using a mload. However, for the above example this is inefficient. Consider the following snippet instead:

contract C {
function add(uint[] calldata arr) external returns (uint sum) {
uint length = arr.length;
for (uint i = 0; i < arr.length; i++) {
sum += arr[i];
}
}
}

In the above snippet, instead of going via memory, the value is directly read from calldata using calldataload. That is, there are no intermediate memory operations that carries this value.

Gas savings: In the former example, the ABI decoding begins with copying value from calldata to memory in a for loop. Each iteration would cost at least 60 gas. In the latter example, this can be completely avoided. This will also reduce the number of instructions and therefore reduces the deploy time cost of the contract.

In short, use calldata instead of memory if the function argument is only read.

Note that in older Solidity versions, changing some function arguments from memory to calldata may cause "unimplemented feature error". This can be avoided by using a newer (0.8.*) Solidity compiler.

Examples Note: The following pattern is prevalent in the codebase:

function f(bytes memory data) external {
(...) = abi.decode(data, (..., types, ...));
}

Here, changing to bytes calldata will decrease the gas. The total savings for this change across all such uses would be quite significant.

Proof Of Concept

Examples:

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/refs/OracleRef.sol#L84

Tools Used

None

Recommended Mitigation Steps

Change memory definition with calldata.

C4-005 : Non-strict inequalities are cheaper than strict ones

Impact

Strict inequalities add a check of non equality which costs around 3 gas.

Proof of Concept

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/oracle/ScalingPriceOracle.sol#L140

Tools Used

Code Review

Recommended Mitigation Steps

Use >= or <= instead of > and < when possible.

C4-006: Use of constant keccak variables results in extra hashing (and so gas).

Impact

That would Increase gas costs on all privileged operations.

Proof of Concept

The following role variables are marked as constant.

  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Permissions.sol::10 => bytes32 public constant override BURNER_ROLE = keccak256("BURNER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Permissions.sol::11 => bytes32 public constant override MINTER_ROLE = keccak256("MINTER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Permissions.sol::13 => keccak256("PCV_CONTROLLER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Permissions.sol::14 => bytes32 public constant override GOVERN_ROLE = keccak256("GOVERN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/Permissions.sol::15 => bytes32 public constant override GUARDIAN_ROLE = keccak256("GUARDIAN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::18 => bytes32 internal constant GOVERNOR = keccak256("GOVERN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::21 => bytes32 internal constant GUARDIAN = keccak256("GUARDIAN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::24 => bytes32 internal constant PCV_CONTROLLER = keccak256("PCV_CONTROLLER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::27 => bytes32 internal constant MINTER = keccak256("MINTER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::34 => bytes32 internal constant PARAMETER_ADMIN = keccak256("PARAMETER_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::37 => bytes32 internal constant ORACLE_ADMIN = keccak256("ORACLE_ADMIN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::41 => keccak256("TRIBAL_CHIEF_ADMIN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::45 => keccak256("PCV_GUARDIAN_ADMIN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::48 => bytes32 internal constant MINOR_ROLE_ADMIN = keccak256("MINOR_ROLE_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::51 => bytes32 internal constant FUSE_ADMIN = keccak256("FUSE_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::54 => bytes32 internal constant VETO_ADMIN = keccak256("VETO_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::57 => bytes32 internal constant MINTER_ADMIN = keccak256("MINTER_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::60 => bytes32 internal constant OPTIMISTIC_ADMIN = keccak256("OPTIMISTIC_ADMIN");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::67 => bytes32 internal constant LBP_SWAP_ROLE = keccak256("SWAP_ADMIN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::70 => bytes32 internal constant VOTIUM_ROLE = keccak256("VOTIUM_ADMIN_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::73 => bytes32 internal constant MINOR_PARAM_ROLE = keccak256("MINOR_PARAM_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::76 => bytes32 internal constant ADD_MINTER_ROLE = keccak256("ADD_MINTER_ROLE");
  2022-03-volt-cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/core/TribeRoles.sol::79 => bytes32 internal constant PSM_ADMIN_ROLE = keccak256("PSM_ADMIN_ROLE");

This results in the keccak operation being performed whenever the variable is used, increasing gas costs relative to just storing the output hash. Changing to immutable will only perform hashing on contract deployment which will save gas.

See: ethereum/solidity#9232 (https://github.com/ethereum/solidity/issues/9232#issuecomment-646131646)

Tools Used

Code Review

Recommended Mitigation Steps

Consider to change the variable to be immutable rather than constant.

C4-007: ERC20 approve method missing return value check

Impact

The following contract functions performs an ERC20.approve() call but does not check the success return value. Some tokens do not revert if the approval failed but return false instead.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2022-03-volt/blob/cec24b859c69d1397ce4048b6e9b8e96410b31dd/contracts/pcv/compound/ERC20CompoundPCVDeposit.sol#L31

2. Tokens that don't actually perform the approve and return false are still counted as a correct approve.

Tools Used

None

Recommended Mitigation Steps

Its recommend to using OpenZeppelin’s SafeERC20 versions with the safeApprove function that handles the return value check as well as non-standard-compliant tokens.

Reference : https://github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.1/contracts/token/ERC20/utils/SafeERC20.sol#L74