Web Real-Time Communication (WebRTC) enables real-time peer-to-peer communication, but its Interactive Connectivity Establishment (ICE) process can unintentionally expose internal and public IP addresses as metadata. This paper presents a cross-platform measurement study of WebRTC metadata leakage using current (2025) builds of Chrome, Brave, Firefox, and Tor on desktop and mobile platforms. Experiments were conducted across semi-trusted Wi-Fi and untrusted mobile carrier networks. Results show that Chrome remains the most leakage-prone, disclosing LAN or Carrier-Grade NAT (CGNAT) addresses on mobile and metadata on desktop; Brave avoids direct IP leaks but exposes session-stable mDNS identifiers; Firefox provides strong protection on desktop but leaks internal IPs on Android; and Tor consistently prevents all forms of leakage. We introduce a structured threat model for semi-trusted environments and evaluate the limitations of mDNS obfuscation. Finally, we propose layered mitigation strategies combining browser defaults, institutional safeguards, and user controls. Findings demonstrate that while direct LAN leakage is declining, emerging vectors such as mDNS and CGNAT create persistent privacy risks requiring protocol-level redesign and policy action.

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