code423n4 commented 2 years ago

Lines of code

https://github.com/code-423n4/2022-08-frax/blob/d968f256462469239ec7394171409ed76dab03e1/src/contracts/FraxlendPair.sol#L261 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L651 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L728 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L819 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L574 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L777 https://github.com/code-423n4/2022-08-frax/blob/b58c9b72f5fe8fab81f7436504e7daf60fd124e3/src/contracts/FraxlendPairCore.sol#L872

Vulnerability details

Use of transfer() instead of call() to send eth

Impact

OZSafeERC20.safeTransfer() relies on transfer() at the end, but with a check of the returning value. Same happens with OZSafeERC20.safeTransferFrom() and transferFrom().

However, the use of transfer() might render ETH impossible to withdraw because after istanbul hardfork, there is increases in the gas cost of the SLOAD operation and therefore breaks some existing smart contracts.Those contracts will break because their fallback functions used to consume less than 2300 gas, and they’ll now consume more, since 2300 the amount of gas a contract’s fallback function receives if it’s called via Solidity’s transfer() or send() methods.

Any smart contract that uses transfer() or send() is taking a hard dependency on gas costs by forwarding a fixed amount of gas: 2300.

References

https://consensys.net/diligence/blog/2019/09/stop-using-soliditys-transfer-now/ https://blog.openzeppelin.com/opyn-gamma-protocol-audit/

Proof of Concept

https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/utils/SafeERC20.sol

library SafeERC20 {
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }