WebRTC Fingerprinting: Why Your Local IP Address Is Leaking Even With a VPN

Most developers know about IP addresses, but WebRTC introduces a subtler privacy problem: your local network IP address can leak even when you're using a VPN . This isn't just a theoretical concern — it's one of the fingerprinting vectors that makes multi-account detection possible. The WebRTC IP Leak Problem WebRTC (Web Real-Time Communication) was designed for peer-to-peer connections like video calls. To establish these connections, browsers need to discover local network interfaces. The problem: browsers expose this information through JavaScript APIs, and it happens even when you're behind a VPN. Basic Detection Code // This reveals local IPs even behind a VPN async function getLocalIPs () { const ips = []; const pc = new RTCPeerConnection ({ iceServers : [{ urls : ' stun:stun.l.google.com:19302 ' }] }); pc . createDataChannel ( '' ); await pc . createOffer (). then ( offer => pc . setLocalDescription ( offer )); return new Promise ( resolve => { pc . onicecandidate = event => { i