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

Typecasting from uint256 to uint64 in `selectWinner` may lead to overflow and incorrect fee calculation (locks fees)

hopeh

Description

The intended behavior is that totalFees accurately tracks accumulated 20% fees so the feeAddress can later withdraw them.

The specific issue is that fee is a uint256 but is cast to uint64 when added to totalFees (a uint64). If the fee exceeds type(uint64).max (~1.8e19 wei ~= 18.44 ETH), the cast silently truncates (Solidity ^0.7.6 casts do not revert), so totalFees records far less than collected.

uint64 public totalFees = 0;
uint256 fee = (totalAmountCollected * 20) / 100; // uint256
totalFees = totalFees + uint64(fee); // @> unsafe narrowing cast truncates above uint64 max

Once the fee (or cumulative total) passes ~18.44 ETH, uint64(fee) wraps and the recorded fees undercount reality.

Risk

Likelihood: Medium

  • A popular raffle easily pushes the fee past ~18.44 ETH; no special attacker action is needed.

Impact: High

  • Fees are lost/unaccounted: totalFees undercounts real fees, and because withdrawFees requires balance == totalFees, the mismatch permanently locks the fee funds.

Proof of Concept

// Enough players so fee > type(uint64).max. totalFees = totalFees + uint64(fee) truncates ->
// totalFees << real fees; withdrawFees (balance == totalFees) never passes -> fees stuck.

Recommended Mitigation

Declare uint256 public totalFees; and drop the narrowing cast, or use a checked cast (SafeCast) that reverts on overflow.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge 7 days 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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