WebKit IP Leaks Can Expose iOS and macOS Users Behind Private Relay and Tor

Security researchers have found WebKit IP leaks that can reveal the real network addresses of iOS and macOS users, even when they use browser-level proxies, iCloud Private Relay, or some Tor-based browsers.

The findings come from Mysk, a privacy-focused development team that investigated reports of DNS leaks in its Psylo browser.

According to the researchers, several WebKit features can bypass a browser’s configured proxy and connect directly from the device. This may expose a user’s IP address or normal DNS infrastructure to websites and other online services.

Device-level VPNs are not affected by the reported issue.

Three WebKit features can bypass proxies

Mysk identified three features that may bypass proxy settings in WebKit, Apple’s browser engine.

The first issue involves DNS prefetching. Websites can use this feature to resolve domain names before a visitor actively opens a link. However, WebKit may send those DNS requests through the device’s normal DNS path instead of through the configured proxy.

That can reveal the DNS servers a person normally uses and potentially disclose information about their network connection.

The second issue involves WebAuthn Related Origin Requests. WebAuthn supports passkeys and other modern authentication methods. Related Origin Requests can allow a passkey to work across connected domains.

However, Mysk said these requests come from the system credential service rather than the browser itself. As a result, they may connect directly to a server without using the configured proxy.

The third issue concerns WebTransport, a newer web communication protocol available from iOS 26.4. The researchers said WebTransport can establish a direct HTTP/3 connection and reveal the device’s real IP address.

Private Relay and Tor browser users may be affected

WebKit IP leaks can affect more than standard Safari users.

Mysk said the problems also affect Apple’s iCloud Private Relay, which is designed to conceal a user’s IP address by routing traffic through two relay servers. The system also encrypts DNS requests so that no single party should see both the user’s identity and the websites they visit.

However, a direct request that bypasses the relay may defeat those protections.

The issue may also affect Tor-based browsers on Apple platforms. Every browser on iOS must use WebKit, which means alternative browsers cannot rely on their own browser engines in the same way they can on desktop operating systems.

Onion browsers are not affected by the WebTransport issue because they have that protocol disabled, according to the researchers.

Risks for users who rely on anonymity

The findings could have serious consequences for people who depend on browser proxies for privacy and safety.

Journalists, activists, politicians, researchers, and people in high-risk environments may use these tools to avoid exposing their home, workplace, or travel-related IP addresses.

A malicious website could potentially trigger a request to an attacker-controlled server. If the request bypasses the proxy, the server could identify the visitor’s real IP address.

An IP address does not always reveal a person’s exact location. Still, it can identify an internet provider, country, city, organisation, or network, depending on the connection.

Psylo blocks risky features by default

Mysk updated its Psylo browser to block DNS prefetch hints and disable WebTransport and WebAuthn by default.

Those changes limit some browser features, but the team said they prevent the identified leak paths. Users can re-enable passkeys and WebTransport through per-silo settings when needed.

The researchers also notified the Tor Project and the developers of Onion Browser about the findings.

Apple had not publicly commented on the report at the time of publication. Until a broader fix becomes available, users who need stronger anonymity should consider a device-level VPN rather than relying only on browser-level proxy protections.