Mullvad warns of Android VPN leak that bypasses kill switch

Mullvad VPN AB said a newly found leak in the Android network stack lets a malicious app send traffic outside the VPN tunnel even when "Block all connections without VPN" is on. The 10 September 2026 privacy blog says that path exposes the device's real IP. Mullvad frames the issue as sitting in Android itself, so it can hit any VPN that relies on that kill-switch toggle, not only Mullvad.

The company published a vendor privacy advisory, not a CVE assignment, a Google security bulletin, or a CISA Known Exploited Vulnerabilities listing. The app needs no special permission. The technique tells Android to create a NAT traversal keep-alive UDP connection offloaded to the Wi-Fi or cellular chip, then misuses that path to send UDP packets on port 4500 to any Internet server. Those packets leave from the network hardware, so they skip the check that all traffic must go through the VPN.

The researcher reported the issue to the Android Vulnerability Reward Program. Mullvad, citing that researcher, says the report was closed without action, the issue is not public, and Mullvad judges Google unlikely to act. CyberInsider, reading the researcher's timeline, says Google marked the submission as a duplicate. Either way, Mullvad's post does not name a public CVE id.

GrapheneOS is aware and working on a fix. Mullvad does not confirm a ship date.

A theoretical mitigation would saturate the limited hardware keep-alive slots so a later malicious app cannot open its own. Mullvad will not ship that workaround. It would still send packets outside the tunnel, and it can lose a race if malware starts first.

Mullvad's guidance is to install only trusted apps, and to prefer a privacy-focused Android fork such as GrapheneOS when that is possible.

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