Security researchers have uncovered a problem that affects the privacy of millions of Apple users: three features of the WebKit engine, the heart of Safari and of every iOS browser, are capable of leaking the device’s real IP address and DNS queries even when browsing with iCloud Private Relay active or through a proxy browser. The finding, published on August 4 by the Mysk team, shows that the anonymity promise of some of these tools is more fragile than it seems.
Three leaks in Apple’s engine
Researchers Tommy Mysk and Talal Haj Bakry detected the problem almost by chance: a user of Psylo, their privacy-focused browser, warned them that some websites were leaking DNS queries despite browsing through a proxy. Upon investigating, they found not one but three WebKit features that bypass the proxy configuration set by the application and send traffic directly from the device.
1. DNS prefetching: the quietest leak
DNS prefetching is an optimization technique through which a page asks the browser to resolve a domain before it needs it, via a <link rel="dns-prefetch"> tag. The problem is that WebKit carries out that resolution through the device’s normal DNS path, completely ignoring the configured proxy. A malicious page can embed unique domain names per visitor in those tags and watch how the queries arrive from the user’s real network instead of from the proxy. This feature arrived on iOS with version 26.0, in September 2025.
2. WebAuthn Related Origin Requests
Passkeys rely on WebAuthn, and its related-origins variant allows a single credential to work across several domains of the same organization. To validate it, the browser must query a JSON file on the server… but that query is not made by the browser engine, but by the operating system’s credential service, which launches the request directly from the device, without going through any proxy. The receiving server sees the user’s real IP, and all of this can happen without user interaction. Available since iOS 18.0.
3. WebTransport: the connection that slips away
WebTransport, the modern, low-latency alternative to WebSocket that runs over HTTP/3 and QUIC, opens the connection directly from the device with its own network parameters, ignoring the session proxy. Any WebTransport server sees the user’s real IP even with iCloud Private Relay active. The API was publicly enabled in iOS 26.4, in March 2026.
iCloud Private Relay is not spared either
The most delicate point is that these three leaks also affect iCloud Private Relay, the privacy service included in iCloud+ that routes Safari traffic through a two-hop relay designed so that not even Apple can see both who you are and which sites you visit. The three leaks occur outside WebKit’s standard page-loading process, so the private relay does not intercept them. The researchers stress that VPNs are not affected: by tunneling all network traffic at the system level, none of these leaks get through them.
The scope is broad. Because App Store policy forces all iOS browsers to use WebKit, any proxy browser on the platform — including Tor browsers for iOS — is vulnerable. Only Onion Browser’s “Silver” security level, which activates Lockdown Mode and disables WebTransport entirely, is safe from this last leak.
Is there real risk?
To date there is no public evidence of active exploitation of these vulnerabilities, and both Apple and security firms classify them as theoretical risk. But the context invites caution: in 2025, Apple fixed two WebKit zero-days that were indeed actively exploited in espionage campaigns against journalists and high-value profiles. A DNS leak allows an attacker to infer what services a person or company uses, a classic first step for targeted phishing attacks.
Mysk has already applied mitigations in Psylo 1.3.1: it blocks DNS prefetching hints and disables WebTransport and WebAuthn by default, with options to re-enable them site by site. Apple, for its part, has fixed part of the problem through background security updates in Safari 26 and the recent versions of its systems, although the researchers warn that the complete solution requires deeper changes in the state handling of WebKit itself.
What you can do
Until a definitive patch arrives, the experts’ recommendation is clear: update your Apple devices to the latest versions of iOS and macOS, do not rely on iCloud Private Relay as your only barrier for truly sensitive tasks and, if you really need to protect your identity, resort to a system-level VPN, which is indeed safe from these leaks. Privacy, once again, proves to be a long-distance race: every new layer of protection brings with it a new way to breach it.
