Question about Security concern for the smart contract

I am working on a project where I have already built a simple smart contract for Auctions. Ps. I am new to smart contract and the only reason I am building this is for a project.

I have built the whole project in Solidity programming language and compiled it using Remix. The Front end is: vue.js, web 3 , bootstrap.

I read a number of articles and now I am confused on how can I show a security breach in my contract.

Auction.sol

I need to demonstrate the security breach or show that my smart contract can break with a line of code or so?