The deprecation of third-party cookies is reshaping the adtech landscape, with a proliferation of alternative solutions promising privacy-preserving audience targeting and measurement. However, our research reveals that many of these approaches introduce subtle yet significant privacy risks that may undermine compliance with regulations like GDPR and CCPA.Through systematic analysis of leading post-cookie adtech solutions, we demonstrate novel techniques to unmask individual users and correlate their behavior across platforms, despite purported anonymization. We show how vulnerabilities in hashed email-based IDs, clean room data matching, and cohort algorithms can be exploited to re-identify users at scale and assemble invasive profiles.We also explore the privacy pitfalls of server-side tracking, where first-party data collection exposes users to backdoor third-party sharing without transparency or control. Drawing on case studies, we illustrate how design flaws in consent management platforms can be subverted to manufacture misleading compliance while enabling unauthorized data processing.Attendees will come away with a clear understanding of the evolving privacy threat landscape in adtech, along with a framework to assess and mitigate risks when implementing new solutions. We'll provide guidance to navigate technical trade-offs and strengthen privacy defenses in a post-cookie world.