Canto Dex Oracle contest - linmiaomiao's results

Lines of code

https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L501 https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L505

Vulnerability details

Impact

Hardcoded prices of stablecosins may open some arbitrage opportunities and produce many bad loans in CLM.

Proof of Concept

Hardcoding price of cUSDT and cUSDC as 1 may open some arbitrage opportunities when real price for each token is a little bit different, and user can borrow more than it actual amount in Canto Lending Market . Also, in case of UST-style collapse, there are exist many bad loans in CLM.

Tools Used

Webstorm

Recommended Mitigation Steps

Don't hardcode cUSDT Price to 1.

Lines of code

https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L581-L584

Vulnerability details

Impact

when calculating token0TVL，it first divide the decimal and then multiplty reserve，it will cause loss of precision and will make LP token price wrong.

Proof of Concept

it calculate token0TVL use :

token0TVL = assetReserves[i] * (prices[i] / decimals)

It first divide the decimal and then multiplty reserve ,and it will result in a loss of price decimal.The result is token0TVL will be much less than the actual value, finally it will cause LPtoken price wrong.

Tools Used

Webstorm

Recommended Mitigation Steps

please calculate like this:

token0TVL = assetReserves[i] * prices[i] / decimals

Lines of code

https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L491 https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L498 https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L501 https://github.com/code-423n4/2022-09-canto/blob/65fbb8b9de22cf8f8f3d742b38b4be41ee35c468/src/Swap/BaseV1-periphery.sol#L505

Vulnerability details

Impact

it compare symbol to identify token，it can be exploit to produce fake price of token.

Proof of Concept

attacker can create a token which is like cToken and has symbol of cNOTE .When somebody call comptroller’s liquidateCalculateSeizeTokens ，it will give an unlisted token with other token(it can be unlisted token or listed token) collateral number.If there are other contracts without whitelist of token and use this price oracle, it will be exploit to produce faked price. It produce a not official hardcode token's price is also a wrong logic.

Tools Used

Webstorm

Recommended Mitigation Steps

use address instead of symbol to identify token