A browser can fake its WebRTC address — it can't fake the packet
Every WebRTC leak check reads a value the browser reports, and an anti-detect browser reports whatever keeps you happy. So I stopped reading its answer and started checking mine: run the STUN server yourself, and whether a packet actually arrived becomes the one thing the browser can’t forge. Here’s the idea, a widget to test your own browser, and an honest tour of everywhere it fails.