Beanstalk: The Finale

Summary

Detect when msg.sender is not used as from in transferFrom.

Vulnerability Details

• ReseedBean::mintAndSync(BeanstalkERC20,address,uint256,uint256) (contracts/beanstalk/init/reseed/L2/ReseedBean.sol#213-224) uses arbitrary from in transferFrom: IERC20(nonBeanToken).safeTransferFrom(OWNER,address(well),tokenAmount) (contracts/beanstalk/init/reseed/L2/ReseedBean.sol#221)

• LibTransfer::transferToken(IERC20,address,address,uint256,LibTransfer.From,LibTransfer.To) (contracts/beanstalk/migration/L1Libraries/LibTransfer.sol#32-48) uses arbitrary from in transferFrom: token.safeTransferFrom(sender,recipient,amount) (contracts/beanstalk/migration/L1Libraries/LibTransfer.sol#42)

• LibTransfer::receiveToken(IERC20,uint256,address,LibTransfer.From) (contracts/beanstalk/migration/L1Libraries/LibTransfer.sol#50-69) uses arbitrary from in transferFrom: token.safeTransferFrom(sender,address(this),amount - receivedAmount) (contracts/beanstalk/migration/L1Libraries/LibTransfer.sol#67)

• LibFertilizer::addUnderlying(uint256,uint256,uint256) (contracts/libraries/LibFertilizer.sol#85-143) uses arbitrary from in transferFrom: IERC20(barnRaiseToken).transferFrom(LibTractor._user(),address(this),uint256(tokenAmountIn)) (contracts/libraries/LibFertilizer.sol#116-120)

• LibTransfer::transferToken(IERC20,address,address,uint256,LibTransfer.From,LibTransfer.To) (contracts/libraries/Token/LibTransfer.sol#29-45) uses arbitrary from in transferFrom: token.safeTransferFrom(sender,recipient,amount) (contracts/libraries/Token/LibTransfer.sol#39)

• LibTransfer::receiveToken(IERC20,uint256,address,LibTransfer.From) (contracts/libraries/Token/LibTransfer.sol#47-66) uses arbitrary from in transferFrom: token.safeTransferFrom(sender,address(this),amount - receivedAmount) (contracts/libraries/Token/LibTransfer.sol#64)

• UnripeFacet::addMigratedUnderlying(address,uint256) (contracts/beanstalk/barn/UnripeFacet.sol#284-295) uses arbitrary from in transferFrom: IERC20(s.sys.silo.unripeSettings[unripeToken].underlyingToken).safeTransferFrom(LibTractor._user(),address(this),amount) (contracts/beanstalk/barn/UnripeFacet.sol#289-293)

In each scenario, the attacker can call the function and specify the user's address as from in transferFrom allowing the attacker to transfer the user's funds to himself.

Impact

Funds can be stolen if the attacker calls the function and specifies the user's address

Tools Used

Slither

Recommendations

Use msg.sender as from in transferFrom.

For example: