Summary

Vulnerability Details

stETH token is given unlimited approval to the unstETH contract. This means that the unstETH contract can transfer an arbitrary amount of stETH tokens from the BridgeSteth contract at any time. If the unstETH contract is compromised, this could lead to a loss of all stETH tokens held in the BridgeSteth contract.

Impact

It could potentially lead to a significant financial loss.

Tools Used

Manual Review

Recommendations

It is recommended to implement a function that only approves the necessary amount of stETH tokens to the unstETH contract when a deposit or unstake operation is about to be performed. This function should be called before each transfer operation, and it should revoke the previous approval (if any) and set a new one for the exact amount to be transferred.