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

Integer overflow of `PuppyRaffle::totalFees` loses fees

joevly

Root + Impact

Description

In solidity versions especially for 0.8.x integers were subject to integer overflow.

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

Risk

Impact:

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. We then have 89 players enter a new raffle and conclude the raffle

  3. totalFees will be:

totalFees = totalFees + uint64(fee);
// Also known as
totalFees = 800000000000000000 + 17800000000000000000
// And this will overflow!
totalFees = 153255926290448384

  1. You will not be able to withdraw, due to the line in PuppyRaffle::withdrawFees:

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

Although you could use selfdestruct to send ETH to this contract in order to for the values to match and withdraw the fees, this is clearly not the intended design of the protocol. At some point, there will be too much balance in the contract that the above require will be impossible to hit.

function testTotalFeesOverflow() public playersEntered {
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
puppyRaffle.selectWinner();
uint256 startingTotalFees = puppyRaffle.totalFees();
// startingTotalFees = 0.8 ETH -> 800000000000000000
​
// We then have 89 players enter a new raffle
uint256 numPlayers = 89;
address[] memory players = new address[](numPlayers);
for (uint256 i; i < numPlayers; i++) {
players[i] = address(i);
}
puppyRaffle.enterRaffle{value: entranceFee * numPlayers}(players);
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
puppyRaffle.selectWinner();
​
uint256 endingTotalFees = puppyRaffle.totalFees();
console.log("starting total fees: ", startingTotalFees);
console.log("ending total fees: ", endingTotalFees);
assert(endingTotalFees < startingTotalFees);
​
// We are also unable to withdraw any fees because of the require check
vm.expectRevert("PuppyRaffle: There are currently players active!");
puppyRaffle.withdrawFees();
}

Recommended Mitigation

There are a few possible mitigations.

  1. Use a newer version of solidity 0.8.x and a uint256 instead of uint64 for PuppyRaffle::totalFees

- pragma solidity ^0.7.6;
+ pragma solidity ^0.8.20;
.
.
.
- uint64 public totalFees = 0;
+ uint256 public totalFees = 0;

  1. You could also use the SafeMath library of OpenZeppelin for version 0.7.6 of solidity. However you would still have a hard time with the uint64 type if too many fees are collected.

  2. Remove the balance check from PuppyRaffle::withdrawFees

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

There are more attack vectors with that final require, so we recommend removing it regardless.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 13 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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