Beedle - Oracle free perpetual lending

Summary

WETH fees sent to the staking contract, if there are no tokens staked, will be lost forever.

Vulnerability Details

Consider the following POC:

import "forge-std/Test.sol";
import "../src/Staking.sol";

import {ERC20, WETH} from "solady/src/tokens/WETH.sol";

contract TERC20 is ERC20 {
    function name() public pure override returns (string memory) {
        return "Test ERC20";
    }
    function symbol() public pure override returns (string memory) {
        return "TERC20";
    }
    function mint(address _to, uint256 _amount) public {
        _mint(_to, _amount);
    }
}

contract StakingTest is Test {

    Staking public staking;

    WETH public wethToken;
    TERC20 public stakingToken;

    address public staker1 = address(0x1);
    address public owner = address(0x3);

    function setUp() public {
        stakingToken = new TERC20();
        wethToken = new WETH();
        vm.deal(owner, 1000 ether);
        vm.startPrank(owner);
        staking = new Staking(address(stakingToken), address(wethToken));
        stakingToken.mint(owner, 100 ether);
        wethToken.deposit{value: 50 ether}();
    }

    function test_rewardsNoTokenStaked() public {
        vm.startPrank(owner);
        stakingToken.transfer(staker1, 20 ether);
        //deposit 10 weth with no token staked.
        wethToken.transfer(address(staking), 10 ether);

        // users stake the tokens
        vm.startPrank(staker1);
        stakingToken.approve(address(staking), 20 ether);
        staking.deposit(20 ether);

        // claim the weth rewards
        vm.startPrank(staker1);
        staking.claim();

        assertEq(wethToken.balanceOf(address(staking)) / 1 ether, 10);
        assertEq(wethToken.balanceOf(address(staker1)) / 1 ether, 0);

        // the first 10 weth are forever stuck on the contract
        console.log("staking contract weth balance", wethToken.balanceOf(address(staking)) / 1 ether);
        console.log("staker 1 eth balance", wethToken.balanceOf(staker1)/ 1 ether);
    }

Impact

Permanent loss of WETH in this specific circumstance.

Tools Used

Foundry

Recommendations

Make sure there is always a small amount of token staked on the staking contract.