⚔️Stopping the Unstoppable Vault

The learning process will be more beneficial for you if you will avoid the hints.

However, if you are frustrated, open these by order of frustration:

Hint 1

The intended issue resides within the UnstoppableVault::flashLoan function.

Read the whole code, including documentation of functions and inner workings, until you properly understand the function.

Hint 2

Try to scrape clues from the success condition on the challenge's prepared test:

after(async function () {
    /** SUCCESS CONDITIONS - NO NEED TO CHANGE ANYTHING HERE */

    // It is no longer possible to execute flash loans
    await expect(
        receiverContract.executeFlashLoan(100n * 10n ** 18n)
    ).to.be.reverted;
});

The test expects the contract to be reverted upon call, what logic triggers the revert method under the UnstoppableVault::flashLoan function?

Although that in a real scenario the tests might not be as indicative of the flaws, they do provide an insight towards the contract developer's mindset.

Hint 3

The goal is to try to transfer funds to the contract directly, affecting the bad-practice balance check it does when calling UnstoppableVault::flashLoan.

You can see in the tests that these too lines are ready for you:

token = await(await ethers.getContractFactory('DamnValuableToken', deployer)).deploy();
vault = await(await ethers.getContractFactory('UnstoppableVault', deployer)).deploy(
    token.address,
    deployer.address, // owner
    deployer.address // fee recipient
);

You need to interact with the token contract through the token variable, and use ERC20 standard to transfer funds directly to the UnstoppableVault contract, accessible through the vault variable.