Puppy Raffle
AI First Flight #1
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EXP
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Submission Details
Severity: high
Valid

`totalFees` is `uint64` and `fee` is unsafely cast — fee accounting overflows/truncates and permanently bricks `withdrawFees`

zanycloud526

Root + Impact

Description

  • Accrued fees should be tracked exactly so the fee address can withdraw them.

  • totalFees is a uint64 and fee (a uint256) is cast to uint64 before adding. Under Solc 0.7.6 there is no overflow check, so a large single fee truncates and repeated rounds wrap, corrupting the fee total.

uint64 public totalFees = 0;
...
uint256 fee = (totalAmountCollected * 20) / 100;
@> totalFees = totalFees + uint64(fee); // uint256 -> uint64 truncation + unchecked add (0.7.6)

Risk

Likelihood:

  • Occurs once cumulative/again single-round fees exceed type(uint64).max (~18.44 ETH), which is reached by a popular raffle with a normal entrance fee and many players.

Impact:

  • totalFees no longer matches the ETH actually held; withdrawFees' check require(address(this).balance == uint256(totalFees)) can never pass, so fees are permanently locked; truncation can also under-count protocol revenue.

Proof of Concept

// With entranceFee and players such that fee = totalAmountCollected*20/100 > type(uint64).max,
// uint64(fee) truncates, e.g. fee = 2^64 + 5 -> uint64(fee) == 5.
// totalFees ends far below the real balance, so withdrawFees() always reverts.

Recommended Mitigation

- uint64 public totalFees = 0;
+ uint256 public totalFees = 0;
...
- totalFees = totalFees + uint64(fee);
+ totalFees = totalFees + fee;
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 6 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-05] Typecasting from uint256 to uint64 in PuppyRaffle.selectWinner() May Lead to Overflow and Incorrect Fee Calculation

## Description ## Vulnerability Details The type conversion from uint256 to uint64 in the expression 'totalFees = totalFees + uint64(fee)' may potentially cause overflow problems if the 'fee' exceeds the maximum value that a uint64 can accommodate (2^64 - 1). ```javascript totalFees = totalFees + uint64(fee); ``` ## POC <details> <summary>Code</summary> ```javascript function testOverflow() public { uint256 initialBalance = address(puppyRaffle).balance; // This value is greater than the maximum value a uint64 can hold uint256 fee = 2**64; // Send ether to the contract (bool success, ) = address(puppyRaffle).call{value: fee}(""); assertTrue(success); uint256 finalBalance = address(puppyRaffle).balance; // Check if the contract's balance increased by the expected amount assertEq(finalBalance, initialBalance + fee); } ``` </details> In this test, assertTrue(success) checks if the ether was successfully sent to the contract, and assertEq(finalBalance, initialBalance + fee) checks if the contract's balance increased by the expected amount. If the balance didn't increase as expected, it could indicate an overflow. ## Impact This could consequently lead to inaccuracies in the computation of 'totalFees'. ## Recommendations To resolve this issue, you should change the data type of `totalFees` from `uint64` to `uint256`. This will prevent any potential overflow issues, as `uint256` can accommodate much larger numbers than `uint64`. Here's how you can do it: Change the declaration of `totalFees` from: ```javascript uint64 public totalFees = 0; ``` to: ```jasvascript uint256 public totalFees = 0; ``` And update the line where `totalFees` is updated from: ```diff - totalFees = totalFees + uint64(fee); + totalFees = totalFees + fee; ``` This way, you ensure that the data types are consistent and can handle the range of values that your contract may encounter.

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