Security researchers have identified multiple behaviors in Apple’s WebKit browser engine that can reveal a user’s real IP address even when traffic is routed through privacy-focused proxy services. The findings suggest that certain browser features may bypass configured proxies, potentially undermining anonymity for people relying on tools such as iCloud Private Relay or proxy-based privacy browsers.
The research was conducted by Talal Haj Bakry and Tommy Mysk, the developers behind Mysk, a company focused on privacy software for Apple platforms. According to their report, they began investigating after users of their own privacy-oriented browser, Psylo, reported unexpected DNS requests that appeared to bypass the application’s proxy configuration.
Their analysis identified three separate WebKit components that can communicate directly over the internet instead of following the browser’s configured proxy path. As a result, websites or network observers may be able to determine a visitor’s actual IP address under certain circumstances.
One issue involves DNS prefetching, a performance feature that resolves domain names before a user actually visits linked resources. Researchers found that these lookups can use the device’s standard DNS configuration rather than the proxy, potentially exposing information about the user’s network.
The second behavior affects WebAuthn Related Origin Requests, a mechanism designed to support passkey authentication across related websites. According to the researchers, these requests originate from Apple’s credential management service instead of the browser itself, allowing them to bypass proxy settings. They warn that a specially crafted website could exploit this behavior to trigger requests revealing the visitor’s actual IP address.
The third issue concerns WebTransport, a modern communication protocol supported by recent WebKit releases. The researchers say WebTransport connections can establish direct HTTP/3 sessions that ignore configured proxy routes, again exposing the originating device’s network address. They noted that browsers with WebTransport disabled, including some Tor-based implementations, are not affected by this specific behavior.
The findings have broader implications because every browser available on iOS is required to use Apple’s WebKit rendering engine. As a result, developers cannot replace the underlying networking behavior with an alternative browser engine, meaning the observed issues may affect multiple browsers built for Apple’s mobile platform.
The researchers also reported that Apple’s iCloud Private Relay can be affected because the identified requests may occur outside the proxy mechanism intended to conceal users’ IP addresses. Private Relay is designed to improve privacy by encrypting DNS traffic and routing internet requests through separate relay servers so that neither Apple nor websites receive a complete picture of a user’s browsing activity. If certain requests bypass that routing process, the intended privacy protections may not apply in those cases.
To reduce the risk, the Mysk team updated its Psylo browser by disabling DNS prefetching, WebTransport, and WebAuthn by default. The developers said these changes eliminate the observed leaks, although some browser functionality may be reduced. Users who require the affected features can enable them individually if needed.
The researchers have also shared their findings with the Tor Project and the developers of Onion Browser, who are expected to evaluate whether similar mitigations are appropriate for their software. At the time the report was published, Apple had not publicly responded to the findings.