Asymmetry contest - sashik_eth's results

Lines of code

https://github.com/code-423n4/2023-03-asymmetry/blob/main/contracts/SafEth/SafEth.sol#L63

Vulnerability details

Impact

First staker can inflate the rate of minting SafEth token per deposited ETH, leading to the loss of next stakers funds.

It's a well-known attack vector, explained for example here.

Proof of Concept

Next scenario possible:

1. Attacker stake 1 wei of ETH on newly deployed SafETH.sol contract, minting 1 wei of SafETH token.
2. Attacker sends 1 WST_ETH token to WstETH derivative address.
3. Next user stake 0.5 ETH, but since the current underlyingValue is 1 ETH (from WST_ETH sent by the attacker) and totalSupply of SafETH is 1 wei - preDepositPrice is overinflated and user mints 0 wei of SafETH, while the attacker could withdraw all staked 1.5 ETH.

Recommended Mitigation Steps

Consider adding a restriction to mint more than 0 wei of SafETH token on stake() function call or sending the first 1000 wei of token to a zero address.