Reentrancy Demo in Hardhat

Initialize Everything

Follow only if you start from scratch. If you clone this GitHub repo, skip this section.

npm install -g yarn
yarn init --yes
yarn add -D hardhat
npx hardhat init

Deploy and Interact with Vault

// in terminal 1, start a localhost hardhat ethereum node
// if you've done so in the underflow terminal, just skip this
npx hardhat node

// in terminal 2, do
npx hardhat run --network localhost .\scripts\deploy.ts
npx hardhat run --network localhost .\scripts\query.ts
npx hardhat run --network localhost .\scripts\deposit.ts

Deploy the Attack

npx hardhat run --network localhost .\scripts\deploy.attack.ts

Attack the Vault

// then run the full attack script
npx hardhat run --network localhost .\scripts\attack.full.ts

// output
--- operator deposit ---
vault balance:  1000000000000000000n
owner balance:  1000000000000000000n
--- attack contract deposit ---
vault balance:  2000000000000000000n
owner balance:  1000000000000000000n
attack contract balance:  1000000000000000000n
--- attacker contract withdraw ---
vault balance:  0n
owner balance:  1000000000000000000n
// ^^^ The attacker steal owner's balance from the vault
attack contract balance:  0n

BONUS POINTS HERE!

You win bonus points if you are first to finish the following tasks correctly (any).

To claim the bonus and secure your position, submit an issue to THIS repo. Include the link to you solution (in a separate github repo). The repo must come with full hack/defence explaination and step by step tutorial on how to run it. The last commit timestamp to the repo must in PRIOR to your issue timestamp (surely you can continue to work on another branch, I will look at the main branch only). Failures to follow the rules disqualify your submission.

How to defend reentrancy attack for this vault? The submission should come with (1) a secured vault contract source code; (2) a script trying to attack (just like the one i provided) but fails; and (3) explaination on how you do it.
Is there any other vulnerabilities (bug) in the code of Vault.sol and Attack.sol ? The submission should come with (1) a bug report, where is the bug, why it is a bug, what is the consequnece of the bug? (2) a script that exploits the bug; and (3) a secured version of the contract source code.