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

Integer overflow of `PuppyRaffle::totalFees` loses fees

hmpippo

Integer overflow of PuppyRaffle::totalFees loses fees

Description

  • In solidity versions prior to 0.8.0 integers were subject to integer overflows.

uint64 myVar = type(uint64).max
// 18446744073709551615
myVar = myVar + 1
// myVar will be 0

Risk

Likelihood: High

  • In PuppyRaffle::selectWinner, totalFees are accumulated for the feeAddress to collect later in PuppyRaffle::withdrawFees. However, if the totalFees variable overflows, the feeAddress may not collect the correct amount of fees, leaving fees permanently stuck in the contract

Impact: High

  • In PuppyRaffle::selectWinner, totalFees are accumulated for the feeAddress to collect later in PuppyRaffle::withdrawFees. However, if the totalFees variable overflows, the feeAddress may not collect the correct amount of fees, leaving fees permanently stuck in the contract

Proof of Concept

  1. We conclude a raffle of 4 players

  2. After many rounds of raffles, the totalFees reach a value close to type(uint64).max

  3. We do another round of raffle, and the totalFees decrease(wrap around) instead of increase

Proof of Code:

Code
function test_totalFeesOverflow() public {
uint256 maxUint = type(uint64).max;
uint256 feeAmount = (entranceFee * 4) * 20 / 100;
uint256 numOfRaffles = (maxUint / feeAmount);
​
for (uint256 i; i < numOfRaffles; ++i) {
address[] memory players = new address[](4);
players[0] = playerOne;
players[1] = playerTwo;
players[2] = playerThree;
players[3] = playerFour;
puppyRaffle.enterRaffle{value: entranceFee * 4}(players);
​
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
​
puppyRaffle.selectWinner();
}
​
address[] memory players = new address[](4);
players[0] = playerOne;
players[1] = playerTwo;
players[2] = playerThree;
players[3] = playerFour;
puppyRaffle.enterRaffle{value: entranceFee * 4}(players);
​
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
​
uint256 prevTotalFees = puppyRaffle.totalFees();
puppyRaffle.selectWinner();
console.log("Total fees before overflow: ", prevTotalFees);
console.log("Total fees after overflow: ", puppyRaffle.totalFees());
assert(puppyRaffle.totalFees() < prevTotalFees);
}

Recommended Mitigation

There are a few recommended mitigations here.
​

  1. Use a newer version of Solidity that does not allow integer overflows by default.

- pragma solidity ^0.7.6;
+ pragma solidity ^0.8.18;

Alternatively, if you want to use an older version of Solidity, you can use a library like OpenZeppelin's SafeMath to prevent integer overflows.
​

  1. Use a uint256 instead of a uint64 for totalFees.

- uint64 public totalFees = 0;
+ uint256 public totalFees = 0;

  1. Remove/Alter the balance check in PuppyRaffle::withdrawFees

- require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!");

We additionally want to bring your attention to another attack vector as a result of this line in a future finding.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 8 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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