Qubit is Mound’s innovative DeFi protocol optimized to deliver “Lending as a utility”. The Qubit protocol was subject to an exploit to our QBridge deposit function.The attacker called the QBridge deposit function on the ethereum network, which calls the deposit function QBridgeHandler. QBridgeHandler should receive the WETH token, which is the original tokenAddress, and if the person who performed the tx does not have a WETH token, the transfer should not occur. tokenAddress.safeTransferFrom(depositer, address(this), amount); In the code, tokenAddress is 0, so safeTransferFrom didn’t fail and the deposit function ended normally regardless of the amount value. Additionally, tokenAddress was the WETH address before depositETH was added, but as depositETH is added, it is replaced with the zero address that is the tokenAddress of ETH. In summary, the deposit function was a function that should not be used after depositETH was newly developed, but it remained in the contract. 77,162 xETH were liquidated.