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

Integer overflow of `PuppyRaffle::totalFees` loses fees

patonguch

Root + Impact

Description

  • Describe the normal behavior in one or more sentences

  • Explain the specific issue or problem in one or more sentences

In solidity versions prior to `0.8.0` integers were subject to integer overflows.
​
```javascript
uint64 myVar = type(uint64).max
// 18446744073709551615
myVar = myVar + 1
// myVar will be 0
```

Risk

Likelihood:

  • Reason 1 // Describe WHEN this will occur (avoid using "if" statements)

  • Reason 2

    *Medium/High*

Impact:

  • Impact 1

    *High*

  • Impact 2

    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:
```javascript
totalFees = totalFees + uint64(fee);
// substituted
totalFees = 800000000000000000 + 17800000000000000000;
// due to overflow, the following is now the case
totalFees = 153255926290448384;
```
4. You will not be able to withdraw due to the line in `PuppyRaffle::withdrawFees`:
​
```javascript
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 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.
​
<details>
<summary>Code</summary>
​
```javascript
function testTotalFeesOverflow() public playersEntered {
// We finish a raffle of 4 to collect some fees
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
puppyRaffle.selectWinner();
uint256 startingTotalFees = puppyRaffle.totalFees();
// startingTotalFees = 800000000000000000
​
// We then have 89 players enter a new raffle
uint256 playersNum = 89;
address[] memory players = new address[](playersNum);
for (uint256 i = 0; i < playersNum; i++) {
players[i] = address(i);
}
puppyRaffle.enterRaffle{value: entranceFee * playersNum}(players);
// We end the raffle
vm.warp(block.timestamp + duration + 1);
vm.roll(block.number + 1);
​
// And here is where the issue occurs
// We will now have fewer fees even though we just finished a second raffle
puppyRaffle.selectWinner();
​
uint256 endingTotalFees = puppyRaffle.totalFees();
console.log("ending total fees", endingTotalFees);
assert(endingTotalFees < startingTotalFees);
​
// We are also unable to withdraw any fees because of the require check
vm.prank(puppyRaffle.feeAddress());
vm.expectRevert("PuppyRaffle: There are currently players active!");
puppyRaffle.withdrawFees();
}
```
</details>

Recommended Mitigation

There are a few recommended mitigations here.
​
1. Use a newer version of Solidity that does not allow integer overflows by default.
```diff
- 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.
​
2. Use a `uint256` instead of a `uint64` for `totalFees`.
```diff
- uint64 public totalFees = 0;
+ uint256 public totalFees = 0;
```
3. Remove the balance check in `PuppyRaffle::withdrawFees`
```diff
- 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 1 hour 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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