"Meta and Yandex are de-anonymizing Android users’ web browsing identifiers", 3 June 2025

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. ...

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.”

The bypass—which Yandex began in 2017 and Meta started last September—allows the companies to pass cookies or other identifiers from Firefox and Chromium-based browsers to native Android apps for Facebook, Instagram, and various Yandex apps. The companies can then tie that vast browsing history to the account holder logged into the app.

This abuse has been observed only in Android, and evidence suggests that the Meta Pixel and Yandex Metrica target only Android users. The researchers say it may be technically feasible to target iOS because browsers on that platform allow developers to programmatically establish localhost connections that apps can monitor on local ports.

In contrast to iOS, however, Android imposes fewer controls on local host communications and background executions of mobile apps, the researchers said, while also implementing stricter controls in app store vetting processes to limit such abuses. This overly permissive design allows Meta Pixel and Yandex Metrica to send web requests with web tracking identifiers to specific local ports that are continuously monitored by the Facebook, Instagram, and Yandex apps. These apps can then link pseudonymous web identities with actual user identities, even in private browsing modes, effectively de-anonymizing users’ browsing habits on sites containing these trackers.

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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.

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A representative for Google said the behavior violates the terms of service for its Play marketplace and the privacy expectations of Android users.

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Meta didn't answer emailed questions for this article, but provided the following statement: "We are in discussions with Google to address a potential miscommunication regarding the application of their policies. Upon becoming aware of the concerns, we decided to pause the feature while we work with Google to resolve the issue."

In an email, Yandex said it was discontinuing the practice and was also in touch with Google.

"Yandex strictly complies with data protection standards and does not de-anonymize user data," the statement added. "The feature in question does not collect any sensitive information and is solely intended to improve personalization within our apps."

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There’s got to be a better way

The various remedies DuckDuckGo, Brave, Vivaldi, and Chrome have put in place are working as intended, but the researchers caution they could become ineffective at any time.

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The researchers warn that the current fixes are so specific to the code in the Meta and Yandex trackers that it would be easy to bypass them with a simple update.

Got consent?

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There's no indication that Meta or Yandex has disclosed the tracking to either websites hosting the trackers or end users who visit those sites. Developer forums show that many websites using Meta Pixel were caught off guard when the scripts began connecting to local ports.

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So far, Google has provided no indication that it plans to redesign the way Android handles local port access. For now, the most comprehensive protection against Meta Pixel and Yandex Metrica tracking is to refrain from installing the Facebook, Instagram, or Yandex apps on Android devices.