Canto Dex Oracle contest - SinceJuly's results

Lines of code

https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L582

Vulnerability details

Impact

When calculating token0TVL, the devision of decimal and price is before the multiplication of reserve, which will cause loss of precision and will make LP token price wrong.

Proof of Concept

The token0TVL is calculated using
token0TVL = assetReserves[i] * (prices[i] / decimals)
Solidity operates only with integers. Thus, if the division is done before the multiplication, the rounding errors can increase dramatically, resulting in the wrong LP Token price.

Tools Used

Visual Studio Code

Recommended Mitigation Steps

It is recommended to perform multiplication before division to avoid precision loss. token0TVL = assetReserves[i] * prices[i] / decimals

Lines of code

https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L490-#L509

Vulnerability details

Impact

Proof of Concept

An exploiter may create a fake tokens whose symbols are cNOTE, cUSDT or cUSDC. When somebody call computrolle’s liquidateCalculateSeizeTokens ，it will give an unlisted token with other token's (it can be unlisted token or listed token) collateral number. If there are other contracts without whitelist of tokens and use Canto as its price oracle, getUnderlyingPrice will be exploited to produce fake price.

Tools Used

Visual Studio Code

Recommended Mitigation Steps

Consider using the address instead of symbol to identify them.

UNUSED INTERNAL FUNCTION

• Position: https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L600-L611
• Description: The function _returnStableBooleans is internal and not used in the contract, it is recommended to remove the function.

HARDCODED PRICES FOR STABLECOINS

• Position: https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L501-L508
• Description: Hardcoding price of cUSDT and cUSDC as 1 may open some arbitrage opportunities when real price for each token is a little bit different. Also, in case of UST-style collapse, the protocol will not be able to liquidate bad loans.