What technical vulnerabilities exist in iCloud Private Relay that could allow third-party tracking?
Executive summary
Researchers and vendors have identified several technical pathways by which iCloud Private Relay may fail to fully hide a user’s IP or be bypassed for tracking: WebRTC/STUN leaks that expose real IPs in Safari’s JavaScript environment, shared egress IPs that create false-positives for IP-based controls, and the practical limits of Private Relay’s Safari-only, dual-relay design compared with a full VPN (researchers and vendors) [1][2][3]. Reporting and community posts also note operational issues — outages, incompatibilities with site functions, and impacts on local network monitoring — which can reduce the feature’s effectiveness [4][5][6].
1. WebRTC/STUN leaks: a browser-level leak that defeats the relay
Security researchers found that Safari did not proxy STUN requests through iCloud Private Relay, so STUN servers could learn a device’s real IP; because Safari exposes ICE (candidate) information to JavaScript, a web page can parse those ICE candidates and recover the real IP address, de-anonymizing the user despite Private Relay [1]. The write-up describes this as present in a specific iOS 15 stable build, meaning the bug is at the intersection of browser behavior and the relay design rather than the two-relay protocol itself [1].
2. Shared egress IPs: anonymity can create collective fingerprinting or blocking
Apple’s model uses shared egress IP addresses representing regions rather than one-to-one addresses. That design prevents simple correlation of IP to an individual user, but it also means many users appear to come from the same exit IPs. Operators report mass traffic from Cloudflare IPs used by Private Relay that can trigger rate limits, WAF bans, or risk-based authentication failures — effectively creating a tracking/identification problem for services that treat IP as an identity or signal [2][7][8]. Those operational side effects can push sites to adopt heuristics that might re-identify or block users in ways that weaken privacy in practice [7][8].
3. Scope limits: Safari-only coverage and DNS nuances
Apple’s documentation and third‑party guides make clear that Private Relay primarily protects Safari browsing (and DNS name resolution) rather than all device traffic; it is not a full-system VPN and will not encrypt non‑Safari app traffic, so trackers embedded in apps or other browsers remain outside its protection [9][3]. Third‑party comparisons explicitly warn consumers that Private Relay is not a substitute for a VPN’s broader protections, leaving other vectors available to trackers [3].
4. Network visibility and enterprise monitoring blindspots
Operational security groups highlight that Private Relay can bypass local network monitoring and protections, meaning institutional defenders lose DNS and browsing telemetry for devices using the feature. REN-ISAC’s advisory recommends organizations decide whether to allow or block Private Relay because it can hide traffic from local security tools [6]. That lack of visibility can indirectly enable tracking by reducing defenders’ ability to detect abuse or anomalous client behavior on their networks [6].
5. Compatibility, outages, and device-level bugs that reduce effectiveness
User communities and troubleshooting guides document repeated outages, “Private Relay not working” errors, and compatibility problems that leave users exposed or force them to disable the feature [4][5]. Separate write-ups note that some sites may not function properly when Private Relay is active, which can push users toward disabling it — a human-factor vulnerability that undermines intended protections [10][2].
6. Where design limits are intentional vs. where bugs are corrective
Apple’s two‑relay design intentionally splits knowledge between an Apple‑run ingress and a third‑party egress so no single party can both see a user’s identity and their destination [9][2]. That architecture limits some attack classes, but browser bugs (e.g., STUN handling) and scope limits are not design drivers and have been exploited or noted by researchers and vendors; fixes for browser-level leaks or policy changes about which traffic is covered require software patches and configuration changes [1][2].
7. Practical takeaways and competing perspectives
Security researchers warn of concrete technical leaks like the WebRTC/STUN issue and browser interactions that can reveal IPs [1]. Industry guides and reviewers emphasize Private Relay’s value as a lightweight Safari privacy layer but stress it is not a VPN substitute and note operational tradeoffs like shared egress IPs, site incompatibilities, and reduced enterprise visibility [3][2][11]. Apple’s documentation presents the dual-relay model as a structural protection preventing any single party from correlating identity and browsing [9]. If you need browser-only privacy for everyday surfing, Private Relay can help; if you need cross-app, system-wide protection or rigorous audit/SLA guarantees, available reporting suggests a VPN or additional controls are the safer choice [3][11].
Limitations: available sources do not provide full patch timelines or confirm whether Apple has fixed each reported leak; for claims about fixed vulnerabilities or current patch status, not found in current reporting.