Yeti Finance contest - defsec's results

Handle

defsec

Vulnerability details

Impact

the teamWallet parameter are used for the onlyTeam modifier. In the state variable , proper check up should be done , other wise error in these state variable can lead to redeployment of contract. If the zero address is assigned to rebalanceManager parameter, that will fail all onlyTeam functions.

Proof of Concept

1. Navigate to the following contract functions.

"https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YetiFinanceTreasury.sol#L29"

2. Adding zero address into the teamWallet leads to failure of onlyTeam only functions.

Tools Used

Code Review

Recommended Mitigation Steps

Add proper zero address validation.

Handle

defsec

Vulnerability details

Impact

++i is more gas efficient than i++ in loops forwarding.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/Dependencies/YetiCustomBase.sol#L36

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/BoringCrypto/BoringERC20.sol#L24

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/TeamAllocation.sol#L66

Tools Used

Code Review

Recommended Mitigation Steps

It is recommend to use unchecked{++i} and change i declaration to uint256.

Handle

defsec

Vulnerability details

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-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/LPRewards/Dependencies/SafeERC20.sol#L72

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/LPRewards/Dependencies/Address.sol#L58

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/LPRewards/Pool2Unipool.sol#L169

Tools Used

Manual Review

Recommended Mitigation Steps

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

Handle

defsec

Vulnerability details

Impact

Yeti protocol allows different tokens to be used as output token. The contracts do not appear to support rebasing/deflationary/inflationary tokens whose balance changes during transfers or over time for the collateral. 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

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L731

Tools Used

Code Review

Recommended Mitigation Steps

Make sure output token for any rebasing/inflation/deflation Add support in contracts for such tokens before accepting user-supplied tokens.

uint256 balanceBefore = getOwnBalance(outputToken);
require(outputToken.safeTransfer(assetId, router, address(this), amount, "Transfer ERC20_TRANSFER_FAILED");
uint256 receivedAmount = getOwnBalance(outputToken) - balanceBefore;

Handle

defsec

Vulnerability details

Vulnerability details

Impact

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

The advantages of versions 0.8.* over <0.8.0 are:

• Safemath by default from 0.8.0 (can be more gas efficient than library based safemath.)
• Low level inliner : from 0.8.2, leads to cheaper runtime gas. Especially relevant when the contract has small functions. For example, OpenZeppelin libraries typically have a lot of small helper functions and if they are not inlined, they cost an additional 20 to 40 gas because of 2 extra jump instructions and additional stack operations needed for function calls.
• Optimizer improvements in packed structs: Before 0.8.3, storing packed structs, in some cases used an additional storage read operation. After EIP-2929, if the slot was already cold, this means unnecessary stack operations and extra deploy time costs. However, if the slot was already warm, this means additional cost of 100 gas alongside the same unnecessary stack operations and extra deploy time costs.
• Custom errors from 0.8.4, leads to cheaper deploy time cost and run time cost. Note: the run time cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.

Proof of Concept

1. The contest repository contracts contain different pragma versions. The contracts pragma version can be updated to 0.8.4 for the gas optimization.

• Affected Contracts

"All Contracts" - Pragma version 0.6.12 is used in the all contracts. (https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/sYETIToken.sol#L2)

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.4.

Handle

defsec

Vulnerability details

Impact

Lower than uint256 size storage instance variables are actually less gas efficient. E.g. using uint8 does not give any efficiency, actually, it is the opposite as EVM operates on default of 256-bit values so uint8 is more expensive in this case as it needs a conversion. It only gives improvements in cases where you can pack variables together, e.g. structs.

Proof of Concept

1. Navigate to the following contracts.

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/AssetWrappers/WJLP/ERC20_8.sol#L11

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/sYETIToken.sol#L37

Tools Used

None

Recommended Mitigation Steps

Consider to review all uint types. Change them with uint256 If the integer is not necessary to present with 8.

Handle

defsec

Vulnerability details

Impact

From Pragma 0.8.0, ABI coder v2 is activated by default. The pragma abicoder v2 can be deleted from the repository. That will provide gas optimization.

Proof of Concept

1. The following contract is using ABI coder v2.

"https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/sYETIToken.sol#L3"

Tools Used

None

Recommended Mitigation Steps

Upgrade pragma to 0.8.0 and After the 0.8.0, ABI coder v2 is activated by default. Upgrade pragma to 0.8.0 version. It is recommended to delete redundant codes.

From Solidity v0.8.0 Breaking Changes https://docs.soliditylang.org/en/v0.8.0/080-breaking-changes.html

Handle

defsec

Vulnerability details

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-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L890

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L699

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L873

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L920

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L929

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/ActivePool.sol#L167

Tools Used

None

Recommended Mitigation Steps

Change memory definition with calldata.

Handle

defsec

Vulnerability details

Impact

!= 0 is a cheaper operation compared to > 0, when dealing with uint.

Proof of Concept

1. Navigate to the following contract sections.

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/BorrowerOperations.sol#L165

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/BorrowerOperations.sol#L290

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/BorrowerOperations.sol#L566

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/BorrowerOperations.sol#L572

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/BorrowerOperations.sol#L913


https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/StabilityPool.sol#L656

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/StabilityPool.sol#L1090

https://github.com/code-423n4/2021-12-yetifinance/blob/main/packages/contracts/contracts/StabilityPool.sol#L1099

Tools Used

None

Recommended Mitigation Steps

Consider to replace > 0 with != 0 for gas optimization.

Handle

defsec

Vulnerability details

Impact

When doing swaps with a Uniswap router from within a contract, there's no need to compute any offset from the current block for the deadline parameter. The router just checks if deadline >= block.timestamp.

Proof of Concept

1. Navigate to the following contract.

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/sYETIToken.sol#L231

Tools Used

None

Recommended Mitigation Steps

The most efficient way to provide deadlines for a router swap is to use a hardcoded value that is far in the future, for example, 1e10.

Handle

defsec

Vulnerability details

Impact

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Proof of Concept

1. Navigate to the following smart contract line.

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L699

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L873

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L920

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/BorrowerOperations.sol#L929

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/ActivePool.sol#L167

Tools Used

None

Recommended Mitigation Steps

Consider to cache array length.

Handle

defsec

Vulnerability details

Impact

It is good to add a require() statement that checks the return value of token transfers or to use something like OpenZeppelin’s safeTransfer/safeTransferFrom unless one is sure the given token reverts in case of a failure. Failure to do so will cause silent failures of transfers and affect token accounting in contract.

Reference: This similar medium-severity finding from Consensys Diligence Audit of Fei Protocol: https://consensys.net/diligence/audits/2021/01/fei-protocol/#unchecked-return-value-for-iweth-transfer-call

Proof of Concept

1. Navigate to the following contracts.
2. transfer/transferFrom functions are used instead of safe transfer/transferFrom on the following contracts.

https://github.com/code-423n4/2021-12-yetifinance/blob/96d3e9a046e3d5fd12decc23c79defdc413cf8a1/packages/contracts/contracts/TroveManagerRedemptions.sol#L229

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/StabilityPool.sol#L947

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/ActivePool.sol#L156

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/DefaultPool.sol#L121

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YETI/CommunityIssuance.sol#L125

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/TeamAllocation.sol#L77

https://github.com/code-423n4/2021-12-yetifinance/blob/1da782328ce4067f9654c3594a34014b0329130a/packages/contracts/contracts/YetiFinanceTreasury.sol#L25

Tools Used

Code Review

Recommended Mitigation Steps

Consider using safeTransfer/safeTransferFrom or require() consistently.