Apple’s iCloud Private Relay, a privacy feature designed to hide users’ IP addresses while browsing in Safari, can be bypassed through several WebKit features that send traffic outside the relay. Security researchers Talal Haj Bakry and Tommy Mysk found that the issue can reveal a user’s real network address even when Private Relay is enabled.
The researchers also created a test website that demonstrates the leak. TechCrunch and 404 Media independently confirmed that the site could reveal their real IP addresses while Private Relay was active.
Three WebKit Features Bypass the Proxy
The problem affects WebKit, Apple’s browser engine used by Safari and all browsers on iOS. The researchers identified three features that can bypass configured proxy connections: DNS prefetching, WebAuthn Related Origin Requests and WebTransport.
Instead of sending all relevant traffic through the proxy, these features can connect directly from the device. That direct connection exposes the user’s real network and therefore the IP address that Private Relay is intended to conceal.
The same weaknesses also affect third-party browsers that use WebKit with proxy systems. Bakry and Mysk discovered the issue while working on Psylo, their own privacy-focused browser.
Private Relay Is Different From a VPN
Private Relay is available to iCloud+ subscribers and primarily protects Safari browsing. Apple says the service sends web requests through two separate internet relays so that no single party can see both the user’s identity and the websites they visit.
The first relay, operated by Apple, can see the user’s IP address but not the destination website. A second relay operated by another provider assigns a temporary IP address and connects to the requested site.
Unlike a conventional VPN, Private Relay does not protect every connection made by the device. Apple describes it primarily as a Safari browsing privacy feature, although it also covers DNS requests.
Researchers Did Not Report the Issue to Apple
Mysk said the researchers chose not to privately disclose the vulnerabilities to Apple before publishing them. He cited previous experiences involving long delays, inconsistent communication and disagreements over the effect of reported issues.
Apple had not publicly responded to the findings when the reports were published. The company’s support documentation continues to state that Private Relay prevents websites from seeing a user’s real IP address and exact location during protected browsing.
The researchers have added mitigations to Psylo version 1.3.1 to prevent the three WebKit features from exposing users’ network addresses through its proxy system.
Featured image credits: Pickpik
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