DEF CON 33 - Escaping the Privacy Sandbox with Client Side Deanonymization Attacks - Eugene Lim
Source: YouTube · DEFCONConference · published Oct 10, 2025 · 25:58
Google's Privacy Sandbox contains critical vulnerabilities that undermine its privacy claims, allowing advertisers to deanonymize users and track browsing history despite being designed as a privacy-preserving alternative to third-party cookies.
Key Takeaways:
• The Privacy Sandbox consists of experimental JavaScript APIs added to Chrome that advertisers must apply to access, creating a "walled garden" controlled by Google
• The Attribution Reporting API tracks ad conversions by registering a "source" when a user views an ad, then matching it with a "conversion" when the user visits the advertiser's site
• Debug reports bypass privacy protections like referral headers, leaking information about where conversions were recorded
• A "destination hijacking" vulnerability was found where Google ads inject potentially ownable domains, allowing creation of a boolean oracle to deanonymize users and track browsing history
Privacy-preserving advertising technology remains fundamentally challenging, with the Privacy Sandbox demonstrating how attempts to satisfy both advertisers and privacy needs create new vulnerabilities.
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First 800 characters of the transcript
Okay, so it's 10:00 and I think we're just going to kick it off. So, thank you again everyone. I know it's Sunday morning on DevCon. Um, last day. So, I really appreciate you guys being here and uh I'm hoping this is a useful one for you guys as well. Um, quick um quick introduction. I'm Eugene. Um, I go by Space Raccoon online and this talk is um escaping the privacy sandbox deep dive edition. So uh on Thursday I kind of talked through some of these um findings in the main stage but I thought this was a good opportunity to kind of break it down a bit more deep dive into some of the techniques and the um ideas I had while researching this topic and give you a bit of insight into the privacy sandbox which is Google's um own ad technology that they're trying to use to replace third party coo…