Sandclock contest - Tomio's results

Handle

Tomio

Vulnerability details

Impact

The implementation for the _transferAndCheckUnderlying function can revert the transaction if the underlying token is implementing a fee on the transfer and transferFrom function, this can happen because when a token implementing a fee on transfer, it actually transfer _amount - fee when doing the transfer. therefore the contract will receive less balance than the amount that was inputted.

Proof of Concept

https://github.com/code-423n4/2022-01-sandclock/blob/main/sandclock/contracts/Vault.sol#L588

Tools Used

Recommended Mitigation Steps

uint256 balanceAfter = totalUnderlying() - balanceBefore;