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A Privacy Shield With a Potential Blind Spot
Apple has spent years building a reputation around privacy, and features such as iCloud Private Relay are a major part of that strategy. The service was designed to make it harder for websites and network providers to identify users by hiding their real IP addresses while browsing in Safari.
But a newly disclosed security issue raises an uncomfortable question: what happens when a supposedly private browsing session triggers a request that never passes through Private Relay at all?
Security researchers Tommy Mysk and Talal Haj Bakry say they discovered a series of issues involving Apple’s WebKit browser engine and the way passkeys are handled. According to their research, websites that support—or even pretend to support—passkeys may be able to determine a user’s real IP address despite iCloud Private Relay being enabled.
The finding is particularly concerning because users do not necessarily have to do anything unusual. A person can simply visit a website and interact with what appears to be a normal authentication feature while a separate operating-system-level request potentially bypasses the privacy protection they believed was active.
What iCloud Private Relay Is Supposed to Do
iCloud Private Relay is Apple’s privacy technology for Safari browsing. It was introduced as part of Apple’s broader effort to reduce the amount of information websites and network providers can collect about users.
Private Relay is not a conventional VPN. Instead of creating a traditional system-wide encrypted tunnel for every application, it primarily protects supported Safari web traffic by separating a user’s identity from the destination they are visiting.
The architecture is designed around multiple relays. One party should know who the user is, while another handles the destination request without receiving the user’s original identifying information.
That distinction is important because enabling Private Relay does not automatically mean every connection made by every application on an Apple device is hidden behind the relay.
The Newly Discovered Privacy Problem
According to Mysk and Haj Bakry, the problem appears when websites use passkeys.
Passkeys are intended to replace traditional passwords with a more secure authentication method based on public-key cryptography and standards such as WebAuthn. Instead of repeatedly sending a password to a website, the device uses cryptographic credentials to prove that the user controls an account.
The security model behind passkeys is generally considered much stronger than passwords. However, the researchers found that some of the communication involved in passkey authentication can happen outside the normal Safari networking path.
That creates the critical privacy problem.
The Request That May Escape Private Relay
The researchers explain that certain passkey-related requests are generated by Apple’s credential services rather than directly by Safari.
Because the request originates outside
In practical terms, a website may see two different network identities during what looks like one browsing session.
Safari traffic can appear to originate from Apple’s Private Relay infrastructure, while a separate passkey-related request can potentially reveal the device’s actual public IP address.
This creates a privacy gap between what the user expects Private Relay to protect and what the operating system may actually expose.
Why IP Addresses Matter
An IP address is not the same thing as a complete digital identity, but it can still provide valuable information.
Depending on the network and circumstances, an IP address can help estimate a user’s geographic location, associate activity with a particular network, correlate sessions, and potentially connect otherwise separated pieces of online activity.
For privacy-conscious users, the important issue is not simply whether an IP address reveals an exact home address. The bigger concern is linkability.
If a website can associate a real IP address with activity that the user expected to be anonymized, one of the important privacy properties of Private Relay can be weakened.
The Passkey Paradox
The discovery highlights an unusual security paradox.
Passkeys were created to improve authentication security, eliminate many password-related attacks, and make account takeovers more difficult. Yet the surrounding implementation can potentially create a privacy problem even when the authentication technology itself remains cryptographically secure.
This distinction matters.
A vulnerability does not necessarily mean passkeys are unsafe for authentication. Instead, the concern is that the network behavior surrounding passkey operations may reveal information that users expected Private Relay to conceal.
Security and privacy are related, but they are not identical.
Why Apple’s WebKit Matters
Apple’s WebKit architecture makes the situation even more significant on iPhones and iPads.
In many regions, third-party browsers on iOS have historically been required to use Apple’s WebKit browser engine. That means an issue rooted in WebKit can potentially affect more than Safari itself.
The researchers reportedly found that at least one browser designed around the Tor anonymity network could also be affected by some of the discovered behaviors.
That possibility is particularly serious because users who choose privacy-focused browsers often do so specifically because they want stronger protection against tracking and network-level identification.
The Tor Browser Concern
Tor is designed around a fundamentally different privacy model.
Rather than simply hiding a user’s IP address behind one intermediary, the Tor network routes traffic through multiple relays so that the destination should not directly learn the user’s original network address.
If an operating-system service independently communicates with a website outside the expected anonymization path, however, the protections provided by the browser or anonymity network can potentially be undermined.
That does not mean Tor itself has suddenly become insecure. Instead, it demonstrates an important principle of modern privacy engineering: the strongest browser-level privacy system cannot necessarily protect traffic generated elsewhere by the operating system.
Apple Was Reportedly Warned
Mysk reportedly informed Apple about the issue.
According to the researchers, Apple characterized the problem as “dire,” indicating that the company understood the potential seriousness of the disclosure.
However, the researchers said Apple did not provide a specific timeline for a fix.
The decision to disclose the research despite the lack of a published remediation schedule also puts pressure on Apple to address the underlying architectural behavior quickly and transparently.
A Pattern Worth Watching
The discovery comes after another privacy-related issue involving Apple’s Hide My Email feature.
That earlier problem reportedly allowed access to a user’s real email address and was subsequently fixed by Apple.
The two issues involve different technologies, but together they illustrate a broader challenge for privacy platforms: privacy features are only as strong as the least-protected component that participates in the communication.
A privacy system can be extremely sophisticated and still fail if one overlooked subsystem sends identifying information directly to a website.
Why This Is More Than a Safari Bug
Calling this merely a “Safari bug” risks missing the larger issue.
Modern Apple devices are ecosystems rather than isolated applications. Browsers interact with operating-system services, credential managers, authentication frameworks, networking components, and cloud services.
A request generated by one component can therefore affect the privacy guarantees advertised by another.
That is exactly why security researchers increasingly examine interactions between components instead of looking at individual applications in isolation.
The Architecture Is the Real Story
The most important lesson from this disclosure may not be the specific passkey implementation.
It is the architecture.
When a privacy feature promises to hide a user’s network identity, every network request capable of interacting with a website needs to be considered.
If Safari is protected but an operating-system service can communicate directly with the same website, there is an opportunity for information to escape.
This is a classic example of how security boundaries can become complicated as operating systems become more integrated.
What Users Should Understand
Users should not interpret this discovery as meaning that every website can automatically retrieve their IP address whenever they use a passkey.
The
The practical impact can therefore depend on the operating-system version, browser implementation, website behavior, and the exact authentication flow being triggered.
Nevertheless, the issue deserves attention because it challenges a core expectation: that Private Relay prevents websites from learning the user’s real IP address during protected browsing.
The Risk of Websites Pretending to Support Passkeys
One particularly interesting aspect of the research is the possibility that a website does not necessarily need to be a legitimate passkey provider to take advantage of the relevant behavior.
If a malicious or privacy-invasive website can trigger the same mechanism, the potential attack surface becomes broader.
This creates an important security lesson: browser features should not be trusted solely because they are associated with a legitimate security technology.
Even a strong technology such as passkeys can become part of a privacy problem if surrounding APIs can be abused or triggered unexpectedly.
The Difference Between Authentication and Privacy
Passkeys solve one problem exceptionally well: authentication.
They help prove that a user possesses a cryptographic credential without requiring the traditional exchange of reusable passwords.
But authentication does not automatically provide anonymity.
A user can authenticate securely while still exposing metadata such as an IP address, browser characteristics, device information, or timing information.
The Apple issue demonstrates why security-conscious users need to think about both who can authenticate them and who can observe their activity.
Why iPhone Users Deserve Special Attention
The issue has particular relevance for iPhone and iPad users because Apple’s tightly controlled browser architecture means WebKit sits underneath many browsing experiences.
Even when a user chooses an alternative browser, the underlying browser engine may still be Apple’s technology in affected environments.
That creates a different security model from desktop platforms where independent browsers can use completely different rendering and networking engines.
In other words, one WebKit-level weakness can have a wider ecosystem impact.
Privacy Features Need Independent Verification
Apple’s privacy marketing is built around strong promises.
That makes independent security research especially important.
Users should not have to blindly trust that a feature is working simply because a switch says “Private Relay” is enabled.
Independent testing, responsible disclosure, browser security research, and transparent vulnerability remediation are essential for validating whether privacy technologies behave as advertised.
The Bigger Web Security Problem
The web is becoming increasingly dependent on browser-to-operating-system integration.
Passkeys are one example. Payment systems, biometric authentication, hardware-backed credentials, notifications, media frameworks, and device APIs increasingly involve communication between the browser and the operating system.
Every new integration creates another security boundary.
And every security boundary creates another possibility for information to cross from one privacy domain into another.
Why This Could Become More Important
As passkeys become more common, authentication requests will increasingly involve operating-system credential managers.
That means privacy researchers will likely pay closer attention to the network behavior surrounding these systems.
The question will no longer be simply whether a browser safely handles a webpage.
Researchers will also ask what the operating system does behind the scenes when the browser calls an authentication API.
That shift in perspective is essential for the next generation of privacy engineering.
Apple’s Response Will Matter
The eventual Apple fix will be important not only because it could protect affected users but because it will show how the company chooses to solve the architectural problem.
A superficial patch might address one specific request.
A stronger solution would ensure that operating-system-generated authentication traffic respects the same privacy boundaries expected by users when Private Relay is enabled.
The second approach would be more difficult but potentially much more durable.
Security Researchers Are Filling an Important Gap
Research from independent security investigators often exposes problems that ordinary users would never notice.
A person can enable a privacy feature, visit a website, and assume everything is protected.
Without specialized testing, they may have no way of knowing that another component of the operating system is communicating directly with the destination.
That is why independent research remains one of the most valuable defenses in the modern technology ecosystem.
What Businesses Should Learn
Companies should also pay attention to this disclosure.
Websites increasingly use passkeys, identity providers, fraud detection systems, device fingerprinting, and IP reputation services.
Security teams should understand exactly what information their authentication infrastructure can receive and from which network path it arrives.
A system that unexpectedly receives a
What Developers Should Learn
Developers should avoid assuming that browser privacy protections automatically apply to every API they invoke.
Whenever a website interacts with an operating-system-level credential service, developers need to understand what network requests are generated, where those requests originate, and what metadata the destination can observe.
Privacy should be treated as an end-to-end property rather than a feature attached to one component.
What Apple Needs to Fix
The ideal fix should ensure that privacy-sensitive authentication operations cannot silently escape a user’s configured network privacy protections.
Apple should also clearly document which traffic Private Relay protects and which traffic remains outside its scope.
Clear technical documentation would help users, developers, browser makers, and security researchers understand the actual boundaries of the system.
What Users Can Do Now
Users who rely heavily on iCloud Private Relay should remain aware that it is not equivalent to a system-wide VPN.
They should also keep iOS, iPadOS, macOS, Safari, and related Apple software updated when security patches addressing the issue become available.
Privacy-conscious users can also monitor Apple’s security advisories and the researchers’ testing resources for updates concerning affected configurations.
The most important step, however, is understanding the limitation: turning on Private Relay does not mean every network connection generated by every component of an Apple device is automatically anonymized.
Deep Analysis: How the Privacy Boundary Can Break
Command 1 — Identify the Trust Boundary
The first step in analyzing a privacy system is identifying where protected traffic enters the privacy layer.
For Private Relay, Safari traffic is expected to use Apple’s relay architecture.
The potential problem begins when another component generates a request independently.
That creates two networking paths where the user may assume there is only one.
Command 2 — Follow the Request Origin
Security researchers need to determine which component actually creates the network request.
If Safari creates it, the request can potentially follow Safari’s normal networking architecture.
If an operating-system credential service creates it, the request may follow a completely different path.
This distinction can determine whether the
Command 3 — Compare the Network Paths
A useful privacy audit compares normal browser traffic against authentication-related traffic.
The key questions are simple:
Does the request use the relay?
Does the destination see the relay address or the user’s actual address?
Is the request generated by Safari or another system service?
These questions reveal whether the privacy boundary is functioning as expected.
Command 4 — Test the Authentication Trigger
Researchers can then examine what happens when a passkey-related operation begins.
The objective is not to attack the credential itself.
Instead, the investigation focuses on the network behavior triggered around the credential operation.
That distinction is critical because the cryptographic security of the passkey can remain intact while network privacy is weakened.
Command 5 — Check Multiple Browser Environments
Because WebKit can underpin multiple iOS browsers, testing should not stop with Safari.
Researchers should compare Safari with other affected browsers and privacy-focused applications that rely on WebKit.
The purpose is to determine whether the issue belongs to a single application or a broader platform component.
Command 6 — Check Multiple Operating Systems
A complete investigation should also compare iOS, iPadOS, and macOS.
Different Apple platforms may implement credential services and networking differently.
A vulnerability affecting one operating system does not automatically mean every Apple device is affected in exactly the same way.
Command 7 — Separate Privacy From Authentication Security
The next analytical step is separating two questions:
Can the attacker steal the credential?
and
Can the attacker identify the
These are completely different security outcomes.
A passkey can remain resistant to credential theft while the surrounding authentication process creates an IP privacy leak.
Command 8 — Evaluate the Website Threat Model
Finally, researchers should examine who could exploit the behavior.
A legitimate website might unintentionally receive the IP address.
A privacy-invasive advertiser could potentially attempt to correlate it.
A malicious website could deliberately trigger authentication-related behavior.
The severity therefore depends not only on the technical flaw but also on who can reach the affected functionality and under what conditions.
What Undercode Say:
Privacy Features Must Protect the Entire Journey
A privacy feature is only meaningful when the entire data journey is protected.
Users do not think about individual operating-system services when they enable Private Relay.
They think, “My IP address is hidden.”
If another system component can expose that address, the user’s mental model and the actual architecture are no longer aligned.
Apple’s Privacy Reputation Raises the Stakes
Apple’s privacy reputation makes issues like this more consequential.
The company has positioned privacy as a defining advantage of its ecosystem.
That means users reasonably expect privacy protections to survive complicated interactions between Safari, WebKit, iCloud, authentication services, and the operating system.
This Is an Architecture Problem
The most concerning part of the disclosure is the interaction between components.
A single isolated bug can often be patched quickly.
An architectural mismatch can require deeper changes because developers must decide which subsystem is responsible for enforcing the privacy boundary.
Passkeys Are Not the Villain
It would be misleading to blame passkeys themselves.
Passkeys remain an important technology for reducing password theft and phishing.
The problem described by the researchers is about how authentication-related networking interacts with another privacy technology.
That distinction should remain clear.
Privacy and Security Need Different Testing
Security testing often asks whether an attacker can steal credentials.
Privacy testing asks a different question: what information can be inferred or exposed even when authentication remains secure?
Modern security programs need both forms of testing.
IP Exposure Can Enable Correlation
A leaked IP address can become more significant when combined with other information.
A website may already know a
Adding the real IP address can make correlation easier.
Tor Users Face a Higher-Expectation Problem
People who use Tor or privacy-focused browsers generally have stronger anonymity expectations.
Any unexpected operating-system request that bypasses an anonymity layer therefore deserves particularly serious investigation.
WebKit Creates Platform-Wide Consequences
When many iOS browsers share an underlying engine, vulnerabilities can affect a larger portion of the ecosystem than users might expect.
Browser diversity can be valuable because it limits the blast radius of engine-specific bugs.
Operating-System APIs Are Becoming Security-Critical
Authentication APIs are no longer simple browser features.
They are bridges between websites and operating systems.
Every bridge needs strong isolation, privacy controls, and careful network handling.
Private Relay Is Not a VPN
Users should continue to understand the distinction.
Private Relay is designed primarily around protecting supported Safari browsing traffic.
A traditional VPN operates at a broader networking layer and can protect traffic from applications that Private Relay does not cover.
Marketing and Technical Reality Must Match
Privacy products depend heavily on user expectations.
If a feature is marketed as protecting a particular type of information, its technical implementation should make that guarantee easy to understand.
Ambiguity creates unnecessary risk.
Independent Research Is Essential
Researchers such as Tommy Mysk and Talal Haj Bakry play an important role by testing assumptions that ordinary users cannot easily verify.
Their work demonstrates why privacy claims should be independently tested rather than accepted purely at face value.
Apple’s Patch Strategy Matters
Apple should ideally address the underlying network boundary rather than simply block one known website technique.
Otherwise, another API or authentication flow could potentially create a similar problem.
Responsible Disclosure Helps Everyone
The reported disclosure process also highlights the importance of communication between researchers and vendors.
Security researchers need enough time to investigate and document vulnerabilities.
Vendors need enough time to create and test reliable fixes.
Users ultimately benefit when both sides communicate responsibly.
The Web Is Becoming More Integrated
Modern browsers increasingly depend on operating-system services.
That integration improves usability but creates new security boundaries.
Every additional integration should therefore be evaluated not only for functionality but also for privacy leakage.
Authentication Can Reveal Metadata
Even when authentication is cryptographically secure, the process can reveal metadata.
Network addresses, timing, device information, and connection behavior can all matter.
Security engineers should consider these signals when designing authentication systems.
Privacy Should Be an End-to-End Property
The strongest privacy designs protect information throughout its entire lifecycle.
Protecting the browser while leaving an operating-system service exposed is not enough.
The system must be evaluated as a whole.
Users Need Better Visibility
Apple could improve transparency by explaining exactly which types of traffic Private Relay covers.
A clearer technical model would help users make better decisions about VPNs, browsers, passkeys, and privacy settings.
Developers Need Better Documentation
Developers should know whether an authentication API generates direct network traffic.
They should also understand what privacy protections apply to those requests.
Without that information, applications can unintentionally create privacy problems.
Privacy Bugs Can Be Difficult to Detect
A traditional crash or account takeover is often obvious.
An IP privacy leak can happen silently.
The user may never see an error, warning, or notification.
That makes privacy testing especially important.
The Problem Could Influence Future Browser Design
Browser vendors may increasingly need to coordinate with operating-system vendors to ensure that authentication services respect browser privacy boundaries.
The separation between browser security and operating-system security is becoming increasingly difficult to maintain.
Apple Has an Opportunity
A strong response could turn this incident into a positive example.
If Apple implements a robust fix and clearly documents the change, it can demonstrate that its privacy architecture is designed to evolve when independent researchers uncover weaknesses.
Privacy Claims Must Be Continuously Tested
No privacy technology should be considered permanently secure.
New APIs, authentication methods, browser engines, and operating-system services constantly change the threat landscape.
Privacy protections need continuous testing just like traditional security controls.
The Most Important Lesson
The biggest lesson is simple:
A privacy switch is not the same thing as a privacy guarantee.
The technology behind that switch must protect every relevant pathway.
What This Means for the Future
As passkeys become standard and operating systems take a larger role in web authentication, similar boundary issues will become increasingly important.
Security researchers will need to examine not only browsers but also the invisible services working behind them.
Apple’s Ecosystem Needs Defense in Depth
Apple’s integrated ecosystem can deliver excellent security when its components work together correctly.
But integration also means a mistake in one component can undermine another.
Defense in depth must therefore extend across the entire platform.
Users Should Stay Updated
The most practical response for users is to keep their devices updated and monitor Apple’s security releases for a patch.
Security vulnerabilities rarely remain static after public disclosure.
Once technical details become available, attackers may study them as well.
The Disclosure Is a Warning, Not a Reason to Panic
This discovery should not lead users to abandon passkeys or assume that every Private Relay session is compromised.
Instead, it should encourage a more realistic understanding of privacy technology.
Strong security is not about believing a feature is perfect.
It is about continuously testing whether the feature actually behaves as promised.
Apple’s Next Move Will Be Watched Closely
The real test now is how Apple responds.
A fast, comprehensive fix would reduce the immediate risk and reinforce confidence in Apple’s privacy architecture.
A slow or incomplete response could raise broader questions about how operating-system services interact with Apple’s privacy guarantees.
Privacy Engineering Is Getting Harder
As devices become smarter and authentication becomes more seamless, the invisible network activity behind ordinary actions becomes increasingly complicated.
That complexity creates opportunities for both stronger security and unexpected privacy leaks.
The iCloud Private Relay issue is a reminder that privacy engineering must keep pace with that complexity.
✅ Passkeys Are Designed as a Password Alternative
Passkeys use public-key cryptography and standards such as WebAuthn to provide authentication without relying on traditional reusable passwords. The technology itself is not the same thing as the reported privacy weakness.
✅ iCloud Private Relay Is Not a Traditional System-Wide VPN
Private Relay primarily protects supported Safari browsing traffic and should not be treated as a conventional VPN that automatically tunnels every connection made by every application on an Apple device.
⚠️ The Reported IP Leak Depends on Specific Conditions
The
Prediction
(+1) Apple Will Likely Patch the Underlying Behavior
Given the reported severity of the issue and Apple’s history of addressing publicly disclosed security and privacy vulnerabilities, the most likely outcome is a software update that modifies how passkey-related network requests interact with Private Relay.
(+1) Privacy Testing Will Expand Beyond Browsers
The incident is likely to encourage researchers to examine operating-system authentication services more aggressively, especially as passkeys become a normal part of web browsing.
(+1) Passkeys Will Continue Growing
Despite the privacy concern, passkeys are unlikely to lose momentum. Their benefits against password theft, credential reuse, and phishing remain significant.
(-1) Privacy Expectations Could Take a Hit
If similar issues repeatedly emerge from interactions between Apple’s privacy technologies and system services, privacy-conscious users may become more skeptical of broad privacy claims.
(+1) Independent Researchers Will Keep Finding Cross-Layer Bugs
The next generation of vulnerabilities is increasingly likely to appear where browsers, operating systems, authentication frameworks, and cloud services intersect.
(-1) Attackers May Exploit Public Research Faster
Once technical details become public, malicious websites and threat actors can study the behavior and look for ways to turn theoretical privacy weaknesses into practical tracking mechanisms.
(+1) The Long-Term Outcome Could Be Stronger Privacy Controls
The most positive outcome would be a deeper architectural change in which operating-system authentication requests automatically respect the user’s active privacy protections instead of relying on individual applications to enforce them.
Final Outlook
The iCloud Private Relay disclosure is important because it challenges something users often take for granted: that enabling a privacy feature means the entire experience is private.
The reality is more complicated.
Modern Apple devices are built from dozens of interconnected services, and a request generated behind the scenes can potentially cross a privacy boundary that the user never knew existed.
That is precisely why this research deserves attention.
The future of privacy will not be determined only by encrypted connections, stronger passwords, or better authentication. It will depend on whether every component involved in a digital interaction respects the same privacy expectations.
For Apple, the challenge is now clear: make sure the privacy promised at the browser level is not quietly undone by the operating system working behind it.
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References:
Reported By: 9to5mac.com
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