“Animation” URL in NFT marketplaces considered harmful for privacy

Abstract

Non-Fungible Tokens (NFTs) are becoming increasingly popular as a way to represent and own digital property. However, the usage of NFTs also prompts questions about privacy. In this work, we show that it is possible to use NFTs to retrieve enough information to fingerprint users. By doing so, we can uniquely associate users with blockchain accounts. This would allow linking several blockchain accounts to the same user. This work focuses on the vulnerabilities presented by some popular NFT marketplaces. Since NFTs may have HTML files embedded, they allow the use of fingerprinting techniques if not handled carefully. Finally, we provide recommendations and countermeasures for the different actors in this ecosystem to avoid these kinds of tracking methods and, in doing so, safeguard user privacy.