How does browser WebRTC leak a user's real IP address even when a VPN is active?

THROUGH DIRECT BROWSER STUN REQUESTS BYPASSING THE TUNNEL'S SYSTEM NETWORK INTERFACE.

The WebRTC protocol is built into all modern browsers for voice calls and video conferences without plugins. A script on an open site can request the network address directly, forcing the browser to send packets past the security gateway.

Hidden Leaks of Local and External Interfaces

To establish a direct P2P connection, WebRTC sends requests to STUN servers to determine the client's real network topology. If the browser or VPN client doesn't block these requests at the socket level, the browser exposes both the local home network IP and the external ISP address, nullifying anonymity.

How to Disable or Shield WebRTC

Disable WebRTC in advanced browser settings (e.g., about:config in Firefox).
Install protective extensions that forcibly block direct STUN packet transmission.
Use VPN clients with a built-in WebRTC Leak protection switch at the driver level.
Test your configuration via specialized online network interface leak scanners.