Skip to content
Request an audit

‹ All findings

TOFT removeCollateral can be used to steal all the balance

Crit/HighTapioca DAO·Code4rena · Omnichain money market · 5th July 2023H-12

Source

removeCollateral -> remove message pathway can be used to steal all the balance of the TapiocaOFT and mTapiocaOFT tokens in case when their underlying tokens is native. TOFTs that hold native tokens are deployed with erc20 address set to address zero, so while minting you need to transfer value.

Proof of Concept

The attack needs to be executed by invoking the removeCollateral function from any chain to chain on which the underlying balance resides, e.g. host chain of the TOFT. When the message is received on the remote chain, I have placed in the comments below what are the params that need to be passed to execute the attack.

solidity
    function remove(bytes memory _payload) public {
    (
        ,
        ,
        address to,
        ,
        ITapiocaOFT.IRemoveParams memory removeParams,
        ICommonData.IWithdrawParams memory withdrawParams,
        ICommonData.IApproval[] memory approvals
    ) = abi.decode(
        _payload,
        (
            uint16,
            address,
            address,
            bytes32,
            ITapiocaOFT.IRemoveParams,
            ICommonData.IWithdrawParams,
            ICommonData.IApproval[]
        )
    );
    // approvals can be an empty array so this is skipped
    if (approvals.length > 0) {
        _callApproval(approvals);
    }

    // removeParams.market and removeParams.share don't matter 
    approve(removeParams.market, removeParams.share);
    // removeParams.market just needs to be deployed by the attacker and do nothing, it is enough to implement IMarket interface
    IMarket(removeParams.market).removeCollateral(
        to,
        to,
        removeParams.share
    );
    
    // withdrawParams.withdraw =  true to enter the if block
    if (withdrawParams.withdraw) {
        // Attackers removeParams.market contract needs to have yieldBox() function and it can return any address
        address ybAddress = IMarket(removeParams.market).yieldBox();
        // Attackers removeParams.market needs to have collateralId() function and it can return any uint256
        uint256 assetId = IMarket(removeParams.market).collateralId();
        
        // removeParams.marketHelper is a malicious contract deployed by the attacker which is being transferred all the balance
        // withdrawParams.withdrawLzFeeAmount needs to be precomputed by the attacker to match the balance of TapiocaOFT
        IMagnetar(removeParams.marketHelper).withdrawToChain{
                value: withdrawParams.withdrawLzFeeAmount // This is not validated on the sending side so it can be any value
            }(
            ybAddress,
            to,
            assetId,
            withdrawParams.withdrawLzChainId,
            LzLib.addressToBytes32(to),
            IYieldBoxBase(ybAddress).toAmount(
                assetId,
                removeParams.share,
                false
            ),
            removeParams.share,
            withdrawParams.withdrawAdapterParams,
            payable(to),
            withdrawParams.withdrawLzFeeAmount
        );
    }
}

Neither removeParams.marketHelper or withdrawParams.withdrawLzFeeAmount are validated on the sending side so the former can be the address of a malicious contract and the latter can be the TOFT's balance of gas token.

This type of attack is possible because the msg.sender in IMagnetar(removeParams.marketHelper).withdrawToChain is the address of the TOFT contract which holds all the balances.

This is because:

  1. Relayer submits the message to lzReceive so he is the msg.sender.
  2. Inside the _blockingLzReceive there is a call into its own public function so the msg.sender is the address of the contract.
  3. Inside the _nonBlockingLzReceive there is delegatecall into a corresponding module which preserves the msg.sender which is the address of the TOFT.
  4. Inside the module there is a call to withdrawToChain and here the msg.sender is the address of the TOFT contract, so we can maliciously transfer all the balance of the TOFT.

Tools Used

Foundry

Recommended Mitigation Steps

It's hard to recommend a simple fix since as I pointed out in my other issues the airdropping logic has many flaws. One of the ways of tackling this issue is during the removeCollateral to:

  • Do not allow adapterParams params to be passed as bytes but rather as gasLimit and airdroppedAmount, from which you would encode either adapterParamsV1 or adapterParamsV2.
  • And then on the receiving side check and send with value only the amount the user has airdropped.