Tracking code that Meta and Russia-based Yandex embed into millions of websites is de-anonymizing visitors by abusing legitimate Internet protocols, causing Chrome and other browsers to surreptitiously send unique identifiers to native apps installed on a device, researchers have discovered. Google says it's investigating the abuse, which allows Meta and Yandex to convert ephemeral web identifiers into persistent mobile app user identities.

The covert tracking—implemented in the Meta Pixel and Yandex Metrica trackers—allows Meta and Yandex to bypass core security and privacy protections provided by both the Android operating system and browsers that run on it. Android sandboxing, for instance, isolates processes to prevent them from interacting with the OS and any other app installed on the device, cutting off access to sensitive data or privileged system resources. Defenses such as state partitioning and storage partitioning, which are built into all major browsers, store site cookies and other data associated with a website in containers that are unique to every top-level website domain to ensure they're off-limits for every other site.

A blatant violation

“One of the fundamental security principles that exists in the web, as well as the mobile system, is called sandboxing,” Narseo Vallina-Rodriguez, one of the researchers behind the discovery, said in an interview. “You run everything in a sandbox, and there is no interaction within different elements running on it. What this attack vector allows is to break the sandbox that exists between the mobile context and the web context. The channel that exists allowed the Android system to communicate what happens in the browser with the identity running in the mobile app.”

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