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Last updated: September 03, 2025

SCWE-096: Missing Token Burn on During Cross-Chain NFT Withdrawal

Stable Version v0.0.1

This content is in the version-(v0.0.1) and still under active development, so it is subject to change any time (e.g. structure, IDs, content, URLs, etc.).

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Relationships

  • CWE-345: Insufficient Verification of Data Authenticity
    CWE-345 Link
  • CWE-664: Improper Control of a Resource Through Its Lifetime
    CWE-664 Link

Description

This weakness occurs when a cross-chain bridge allows withdrawals from Chain B to Chain A without properly burning or locking the corresponding token on the source chain (Chain B) before initiating the cross-chain transaction.

As a result, the same token can exist simultaneously on both chains, enabling a double-spend scenario where malicious actors can sell, transfer, or use the same token on multiple chains.

Remediation

  1. Burn the NFT

    • Call the burn(tokenId) function on the L2 NFT contract before sending the cross-chain withdrawal request.
    • This ensures that the NFT no longer exists on L2 and cannot be reused, transferred, or sold.

  2. Alternatively, Lock the NFT (if burning isn’t possible)

    • If NFTs are not meant to be permanently destroyed, implement a lock mechanism to freeze the token on L2 until the cross-chain withdrawal is completed successfully.

  3. Update Cross-Chain Workflow

    • Enforce the burn/lock operation as part of the withdrawal process.
    • Revert the entire transaction if the burn/lock fails.

Examples

  • Vulnerable Code (Not Burning Token Before Sending Cross Chain Message)

    // SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract SourceChainNFTGateway {
    mapping(address => mapping(uint256 => address)) public ownerOf;

    function withdrawNFT(address l2Token, uint256 tokenId) external {
        require(ownerOf[l2Token][tokenId] == msg.sender, "Not the owner");

        // ❌ Send cross-chain message to Destination Chain (omitted for simplicity)
        // NFT is still available on Source Chain → double-spend possible
    }
}

  • Safe Code (Burning Token Before Sending Cross Chain Message) 

    // SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

interface IL2NFT {
    function burn(uint256 tokenId) external;
}

contract SourceChainNFTGateway {
    mapping(address => mapping(uint256 => address)) public ownerOf;

    function withdrawNFT(address l2Token, uint256 tokenId) external {
        require(ownerOf[l2Token][tokenId] == msg.sender, "Not the owner");

        // ✅ Burn the NFT on Source Chain to prevent double-spend
        IL2NFT(l2Token).burn(tokenId);

        // Send cross-chain message to Destination Chain (omitted for simplicity)
    }
}