Better link? https://arstechnica.com/security/2025/06/meta-and-yandex-are-de-anonymizing-android-users-web-browsing-identifiers/

Meta and Yandex achieve the bypass by abusing basic functionality built into modern mobile browsers that allows browser-to-native app communications. The functionality lets browsers send web requests to local Android ports to establish various services, including media connections through the RTC protocol, file sharing, and developer debugging.

While the technical underpinnings differ, both Meta Pixel and Yandex Metrica are performing a “weird protocol misuse” to gain unvetted access that Android provides to localhost ports on the 127.0.0.1 IP address. Browsers access these ports without user notification. Facebook, Instagram, and Yandex native apps silently listen on those ports, copy identifiers in real time, and link them to the user logged into the app.