GrapheneOS before 2026050400 allows attackers to discover the real IP address of a VPN user as a consequence of a registerQuicConnectionClosePayload optimization, because an application can let system_server transmit UDP traffic on its behalf. This occurs when the "Block connections without VPN" and "Always-on VPN" settings are enabled.
https://lowlevel.fun/posts/tiny-udp-cannon-android-vpn-bypass/
https://grapheneos.org/releases#2026050400
https://cyberinsider.com/grapheneos-fixes-android-vpn-leak-google-refused-to-patch/