Tor, Private Relay, and other browser-level proxies don’t protect iOS and macOS users

Modern browsers on iOS and macOS were found to leak real user IPs despite the use of built-in proxy configurations. Users of Apple iCloud Private Relay and even Tor browsers are affected, according to a report by Mysk.

WebKit, the core rendering engine for browsers in the Apple ecosystem, disregards proxy configurations and often sends requests to DNS servers or websites directly, revealing real users’ IPs and jeopardizing any efforts to stay private online. Only device-level VPNs are unaffected.

The startling discovery was made by Mysk, a team of two developers, Talal Haj Bakry and Tommy Mysk, building privacy-preserving apps for Apple platforms.

“Three WebKit features – DNS prefetching, WebAuthn Related Origin Requests, and WebTransport – that bypass the configured proxy and send traffic directly from the device, which exposes the user’s real network. The same leaks also affect Apple’s iCloud Private Relay,” the Mysk report warns.

The team found issues with WebKit after their own Psylo browser was reported by users to leak DNS while visiting certain websites.

We immediately started looking into it.

Mysk

Privacy relays protect users by proxying their traffic through a network of servers that hide the users' real IP addresses.

Every browser on iOS is required by Apple to use WebKit. However, this engine leaks user information in 3 ways:

• DNS prefetching: lets websites resolve domains in advance of when they're actually needed, but uses the device’s normal DNS path, revealing the user’s real DNS servers instead of the proxy’s. If a website includes HTML tag, WebKit skips proxy configuration and goes directly.
• WebAuthn Related Origin Requests: are issued directly from the device. WebAuthn is the standard for passkey authentication, and “Related Origin Requests” allow reusing the same passkey across multiple domains. The problem – these requests are issued by the system’s credential service rather than Safari or other WebKit browsers, bypassing proxy configuration. A malicious website can exploit this by tricking the system into visiting an attacker-controlled server, exposing the real IP address.
• WebTransport: the new communication protocol available since iOS 26.4, also opens an HTTP/3 connection directly and bypasses the proxy, exposing the device’s real IP address. Onion browsers aren’t affected because they have WebTransport disabled.

The potential implications are massive because many journalists, politicians, activists, and others who rely on browser-built-in proxies to protect their privacy weren’t truly private online, and their IP addresses were potentially visible.

Cybernews has reached out to Apple for a comment and will update this story with its response.

Mysk team said they updated their Psylo privacy browser to block DNS prefetch hints, disable WebTransport, and WebAuth by default. This limits some browser functionality but makes the browser leak-free.

“Passkeys and WebTransport have legitimate uses, so both can be re-enabled at any time through per-silo toggles,” Mysk said.

The team also alerted the Tor Project and the developers of Onion Browser on iOS, who will likely release their own fixes soon.

According to Apple documentation, iCloud Private Relay, part of an iCloud+ subscription, is designed to protect user privacy by ensuring that no single party, including Apple, can see what users are doing or what they’re visiting.

Private Relay is supposed to encrypt DNS records and requests, and hide IP addresses by routing traffic through two intermediate relay servers before connecting users to the actual website.