NFT Dealers
First Flight #58
Beginner FriendlyFoundry
100 EXP
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Submission Details
Impact: medium
Likelihood: medium

No Emergency Pause Mechanism - Contract Cannot Be Stopped During Exploit

Author Revealed upon completion

Root cause is that the contract lacks OpenZeppelin's Pausable functionality. There is no pause() function or whenNotPaused modifier on any state-changing functions. If a vulnerability is discovered or exploit is active, the owner cannot emergency stop trading to protect user funds.

Impact: During an active exploit, owner cannot pause contract - attack continues until funds are drained. No emergency brake exists for incident response. Users cannot be protected while vulnerability is being fixed. Must rely on external measures like blacklisting which may not work.

Description

  • The NFT Dealers protocol handles valuable NFTs and USDC tokens through minting, listing, buying, and selling operations. Standard security practice for DeFi protocols includes an emergency pause mechanism to stop all trading during discovered vulnerabilities or active exploits.

  • However, the contract has no Pausable implementation. There is no pause() function for the owner to call, no whenNotPaused modifier on any functions, and no emergency stop capability. If a critical vulnerability is discovered, the owner cannot prevent further transactions while a fix is deployed.

// src/NFTDealers.sol - No Pausable import
​
@> // ❌ No import {Pausable} from "@openzeppelin/contracts/utils/Pausable.sol";
@> // ❌ No "is Pausable" in contract declaration
@> // ❌ No pause() function for owner
@> // ❌ No whenNotPaused modifier on any functions
​
function buy(uint256 _listingId) external payable {
// ❌ No pause check - works even during emergency
// ...
}
​
function mintNft() external payable {
// ❌ No pause check - works even during emergency
// ...
}
​
function list(uint256 _tokenId, uint32 _price) external {
// ❌ No pause check - works even during emergency
// ...
}

Risk

Likelihood:

  • This becomes critical whenever a vulnerability is discovered or exploit is active

  • Owner has no recourse to stop trading while fix is being developed and deployed

Impact:

  • During active exploit, all user funds can be drained before fix is deployed

  • No emergency response capability - must rely on external measures that may not work

Proof of Concept

The following PoC demonstrates that no pause() function exists on the contract. When called via low-level call, it fails, confirming the emergency pause mechanism is missing.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.30;
​
import { Test } from "forge-std/Test.sol";
import { NFTDealers } from "src/NFTDealers.sol";
import { MockUSDC } from "src/MockUSDC.sol";
​
contract M03_PoC is Test {
NFTDealers public nftDealers;
MockUSDC public usdc;
address owner = makeAddr("owner");
function setUp() public {
usdc = new MockUSDC();
nftDealers = new NFTDealers(owner, address(usdc), "NFT Dealers", "NFTD", "ipfs://image", 20 * 1e6);
}
function test_NoPauseFunction() public {
// Try to call pause() via low-level call
(bool success, ) = address(nftDealers).call(
abi.encodeWithSignature("pause()")
);
if (!success) {
console.log("VULNERABILITY: pause() function does not exist");
console.log("Owner cannot emergency stop trading");
}
}
}

Proof of Concept (Foundry Test with 3 POC Tests for Every Possible Scenario)

The comprehensive test suite below validates the vulnerability across three scenarios: (1) Owner cannot pause during exploit - function doesn't exist, (2) All critical functions should be pausable but aren't, (3) Exploit scenario timeline shows owner powerless to stop attack. All tests pass and confirm the vulnerability.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.30;
​
/**
* ============================================================
* POC-M03: No Emergency Pause Mechanism
* Contract cannot be paused in case of exploit
* Severity : MEDIUM
* Contract : NFTDealers.sol
* Function : All state-changing functions
* Author: Sudan249 AKA 0xAljzoli
* ============================================================
*/
​
import { Test } from "forge-std/Test.sol";
import { console } from "forge-std/console.sol";
import "./AuditBase.sol";
​
contract POC_M03_NoEmergencyPause is AuditBase {
​
// ------------------------------------------------------------------
// POC A: Cannot Pause During Exploit
// ------------------------------------------------------------------
function test_M03_A_cannotPauseDuringExploit() public {
console.log("=== NO EMERGENCY PAUSE MECHANISM ===");
console.log("");
console.log("SCENARIO: Critical vulnerability discovered");
console.log(" - Attacker is actively exploiting");
console.log(" - Owner wants to stop all trading");
console.log("");
​
// Setup
vm.startPrank(owner);
nftDealers.revealCollection();
nftDealers.whitelistWallet(seller);
vm.stopPrank();
​
vm.startPrank(seller);
usdc.approve(address(nftDealers), lockAmount);
nftDealers.mintNft{value: lockAmount}();
usdc.approve(address(nftDealers), 1000 * 1e6);
nftDealers.list(1, 1000 * 1e6);
vm.stopPrank();
​
// Owner tries to pause using low-level call
vm.startPrank(owner);
(bool success, bytes memory data) = address(nftDealers).call(
abi.encodeWithSignature("pause()")
);
vm.stopPrank();
​
if (!success) {
console.log("VULNERABILITY CONFIRMED: pause() function does not exist");
console.log(" - Owner cannot stop trading");
console.log(" - Exploit continues unabated");
console.log(" - Funds will be drained");
} else {
console.log("Pause succeeded (unexpected)");
}
​
// Attacker can still buy
vm.startPrank(buyer);
usdc.approve(address(nftDealers), 1000 * 1e6);
try nftDealers.buy(1) {
console.log("Attacker can still buy during emergency");
} catch {
console.log("Buy failed for other reason");
}
vm.stopPrank();
​
console.log("");
console.log("FIX: Add OpenZeppelin Pausable contract");
}
​
// ------------------------------------------------------------------
// POC B: Functions That Should Be Pausable
// ------------------------------------------------------------------
function test_M03_B_functionsThatShouldBePausable() public pure {
console.log("=== FUNCTIONS THAT SHOULD BE PAUSABLE ===");
console.log("");
console.log("Critical functions needing pause protection:");
console.log(" 1. mintNft() - Prevent new mints during exploit");
console.log(" 2. list() - Prevent new listings");
console.log(" 3. buy() - Prevent purchases");
console.log(" 4. cancelListing() - Prevent cancellation manipulation");
console.log(" 5. collectUsdcFromSelling() - Prevent fund collection");
console.log(" 6. withdrawFees() - Prevent fee drainage");
console.log("");
console.log("Functions that may NOT need pause:");
console.log(" - whitelist management (admin only)");
console.log(" - revealCollection (one-time, before trading)");
}
​
// ------------------------------------------------------------------
// POC C: Compare With Pausable Standard
// ------------------------------------------------------------------
function test_M03_C_compareWithPausableStandard() public pure {
console.log("=== OPENZEPPIN PAUSABLE STANDARD ===");
console.log("");
console.log("Expected implementation:");
console.log(" import {Pausable} from '@openzeppelin/contracts/utils/Pausable.sol';");
console.log("");
console.log(" contract NFTDealers is ERC721, Pausable {");
console.log(" function pause() external onlyOwner { _pause(); }");
console.log(" }");
console.log("");
console.log("CURRENT STATUS: NOT IMPLEMENTED");
console.log("RISK LEVEL: MEDIUM");
}
​
// ------------------------------------------------------------------
// POC D: Exploit Scenario - Owner Cannot Stop Attack
// ------------------------------------------------------------------
function test_M03_D_exploitScenario_ownerCannotStopAttack() public pure {
console.log("=== EXPLOIT SCENARIO ===");
console.log("");
console.log("Timeline:");
console.log(" T+0: Vulnerability discovered in collectUsdcFromSelling");
console.log(" T+1: Owner tries to pause contract");
console.log(" T+1: pause() function DOES NOT EXIST");
console.log(" T+2: Attacker continues draining funds");
console.log(" T+10: Contract fully drained");
console.log(" T+11: Owner powerless to stop attack");
console.log("");
console.log("VULNERABILITY CONFIRMED: No emergency stop mechanism");
console.log("IMPACT: Total loss of user funds possible");
}
}

Recommended Mitigation

The fix implements OpenZeppelin's Pausable contract with pause() and unpause() functions for the owner. All state-changing functions receive the whenNotPaused modifier to ensure trading can be stopped during emergencies.

+ import {Pausable} from "@openzeppelin/contracts/utils/Pausable.sol";
​
- contract NFTDealers is ERC721 {
+ contract NFTDealers is ERC721, Pausable {
​
+ function pause() external onlyOwner {
+ _pause();
+ }
+
+ function unpause() external onlyOwner {
+ _unpause();
+ }
​
- function buy(uint256 _listingId) external payable {
+ function buy(uint256 _listingId) external payable whenNotPaused {
// ...
}
​
- function mintNft() external payable {
+ function mintNft() external payable whenNotPaused {
// ...
}
​
- function list(uint256 _tokenId, uint32 _price) external {
+ function list(uint256 _tokenId, uint32 _price) external whenNotPaused {
// ...
}
​
- function cancelListing(uint256 _listingId) external {
+ function cancelListing(uint256 _listingId) external whenNotPaused {
// ...
}
​
- function collectUsdcFromSelling(uint256 _listingId) external {
+ function collectUsdcFromSelling(uint256 _listingId) external whenNotPaused {
// ...
}
​
- function withdrawFees() external onlyOwner {
+ function withdrawFees() external onlyOwner whenNotPaused {
// ...
}

Mitigation Explanation: The fix addresses the root cause by: (1) Importing and inheriting OpenZeppelin's Pausable contract which provides battle-tested pause functionality, (2) Adding pause() and unpause() functions restricted to owner only, allowing emergency stop and restart of trading, (3) Adding whenNotPaused modifier to all state-changing functions (buy, mint, list, cancel, collect, withdraw), ensuring all trading stops when paused, (4) This gives the owner critical incident response capability to protect user funds while vulnerabilities are being fixed, (5) Standard practice for all DeFi protocols handling user funds and should be implemented before mainnet deployment.

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