What is a WebRTC Leak?

A WebRTC leak is when a browser reveals IP addresses used for Web Real-Time Communication (WebRTC) signaling, including your true public IP, even if normal HTTP traffic goes through a VPN or privacy tunnel. It happens because ICE (Interactive Connectivity Establishment) gathers connection “candidates” (local and public IPs) to set up peer connections, and scripts can read those candidates.

How WebRTC exposes IPs

WebRTC can use STUN servers to discover the client’s public address. The browser may collect multiple candidates: VPN interface addresses, physical LAN addresses, and the ISP-facing public IP. Malicious or analytics scripts can create a peer connection solely to harvest candidates, not to place a real call.

VPN clients differ: some force WebRTC through the tunnel or block local candidate types; others leave a side path open. Browser extensions and settings (for example, in Firefox’s about:config) can reduce leaks. Users who need strong anonymity often use hardened browsers designed to block or sanitize WebRTC.

Legitimate services (video chat, some CDNs) use WebRTC for real media paths; the issue is silent candidate harvesting on unrelated pages.

Why this matters for fraud, VPNs, and traffic quality

Advertisers and anti-fraud vendors sometimes compare the IP seen on HTTP requests with addresses surfaced via WebRTC. A mismatch can mean VPN use, misconfigured proxy, or spoofed headers. Not every mismatch is fraud, but it is a signal for risk models that already weigh ISP type, datacenter ranges, and velocity.

Click fraud rings may route clicks through cheap proxies while scripts still leak a different egress IP, helping detectors separate disguised automation from typical consumer paths. Understanding WebRTC leaks clarifies why “IP only” blocking is incomplete and why teams layer detection with behavior and device data for click fraud and ad fraud. Operational hardening for marketers appears in resources such as blocking VPN traffic where policy allows.