Summary

According to the contest details, any token that follows the ERC20 standard can be whitelisted as collateral, Fee on Transfer Tokens are ERC20 tokens that charge a fee on every transfer so, the total amount received is less than the amount transferred.

Vulnerability Details

The transfer functions checked that the from balance after the transfer must be equal to fromBalanceAft != fromBalanceBef - _amount)and the to the balance should be equal to toBalanceAft != toBalanceBef + _amount , if they are not equal it is going to revert the transaction. For the fee on transfer token, the balance of the receiver is always less than the sent amount.

Impact

It is not going to work the transaction will revert.

Tools Used

Manual Analysis

Recommendations

1. Don't Whitelist fees on transfer tokens

2. Modify the transfer function to this.

   function _transfer(

   address _token,

   address _from,

   address _to,

   uint256 _amount,

   address _capitalPoolAddr

   - ) internal {

   + ) internal returns(uint256) {

   uint256 fromBalanceBef = IERC20(_token).balanceOf(_from);

   uint256 toBalanceBef = IERC20(_token).balanceOf(_to);

   ​

   if (

   _from == _capitalPoolAddr &&

   IERC20(_token).allowance(_from, address(this)) == 0x0

   ) {

   ICapitalPool(_capitalPoolAddr).approve(address(this));

   }

   ​

   _safe_transfer_from(_token, _from, _to, _amount);

   ​

   uint256 fromBalanceAft = IERC20(_token).balanceOf(_from);

   uint256 toBalanceAft = IERC20(_token).balanceOf(_to);

   ​

   - if (fromBalanceAft != fromBalanceBef - _amount) {

   - revert TransferFailed();

   - }

   ​

   - if (toBalanceAft != toBalanceBef + _amount) {

   - revert TransferFailed();

   - }

   + return toBalanceBef - toBalanceAft;

   }