Android 16 VPN Bypass via QuicConnectionClosePayload (Tiny UDP Cannon)

Vulnerability Overview Title: The Tiny UDP Cannon: An Android VPN Bypass Core Principle: On Android 16, regular applications can bypass "Always-on VPN" and "Always VPN" settings without special permissions, sending packets directly via the physical Wi-Fi interface and thereby leaking the user's real IP address. Technical Details: 1. Background: Android's holds the permission, allowing it to bypass the firewall and access the physical network directly. 2. Trigger Point: Android 16 introduced a feature for quickly closing QUIC connections ( ). 3. Exploitation: An attacker application calls this hidden API via Binder, passing arbitrary byte payloads. Upon receipt, creates a UDP socket, binds the source address to the device's Wi-Fi IP, and sends the payload to the specified target. 4. Bypass Mechanism: Since this operation is executed by , it is not subject to VPN locking restrictions based on application UID. Packets are sent directly from the physical network interface, bypassing the VPN tunnel. Impact Scope Affected Systems: Android 16 (API 36) and subsequent versions. Affected Devices: Confirmed reproducible on Pixel 8 (Android 16). Affected Scenarios: When the user enables "Always-on VPN" or "Only use VPN for selected apps" and has a VPN active, attacker applications can bypass the VPN to leak the real IP. Permission Requirements: Only and permissions are required (permissions normally granted to standard applications). Remediation Temporary Mitigation: Disable the feature via . Command: Effect: Disables the feature, but requires a restart to take effect. Long-term Fix: It is recommended that the Android Security Team add a caller UID permission check within , or restrict usage to specific system services only. POC Code Extraction 1. Exploitation Code (Java) 2. Mitigation Command

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Android 16 VPN Bypass via QuicConnectionClosePayload (Tiny UDP Cannon)