Understanding the iOS VPN Bypass Vulnerability and Mitigation Strategies

Overview of the iOS VPN Bypass Issue

A critical vulnerability in Apple’s iOS affects how Virtual Private Networks (VPNs) handle network traffic encryption. Identified in iOS versions up to 16, this flaw prevents VPNs from fully encrypting all connections, potentially exposing user data or IP addresses. This post explores the technical details of this issue, its implications for IT professionals, and practical mitigation steps for advanced users.

How the iOS VPN Bypass Vulnerability Works

Under normal circumstances, a VPN client on a device closes all active internet connections and reroutes them through a secure VPN tunnel. This ensures all traffic is encrypted and the user’s real IP address remains hidden. However, in affected iOS versions, certain pre-existing connections fail to close when the VPN is activated. These connections, which may persist for minutes or hours, bypass the VPN tunnel entirely.

A notable example involves Apple’s push notification service, which maintains persistent connections to Apple servers. Other applications, such as messaging apps or services using web beacons, may also be affected. If these connections lack their own encryption, sensitive data could be exposed. More commonly, this vulnerability leads to IP leaks, revealing the user’s true IP address and the destination server’s IP to potential attackers.

Technical Impact

• IP Exposure: Attackers on the same network (e.g., public Wi-Fi) can identify the user’s real IP and the servers they connect to.
• Data Risk: Unencrypted connections outside the VPN tunnel may expose sensitive information, though most modern services use HTTPS, reducing this risk.
• Targeted Threats: Users in regions with heavy surveillance or restricted internet access face heightened risks due to potential monitoring.

The Common Vulnerability Scoring System (CVSS) rates this issue as medium severity due to its potential for IP leaks and limited data exposure risks.

Investigating the Vulnerability

To analyze this issue, network traffic from an iOS device can be captured using tools like Wireshark. When a VPN is active, only traffic between the device and the VPN server (or local network devices) should be visible. However, captures reveal direct connections to external servers, such as those owned by Apple, bypassing the VPN tunnel.

Example Network Traffic

This confirms that certain connections remain active outside the VPN, undermining its security guarantees.

Mitigation Strategies for IT Professionals

Since iOS restricts VPN applications from terminating existing network connections, no VPN service can fully resolve this issue independently. However, advanced users can adopt workarounds to minimize risks until Apple provides a comprehensive fix.

Recommended Mitigation Steps

• Airplane Mode Toggle:
  1. Connect to a VPN server using a reliable provider. For setup guidance, see our VPN setup guide.
  2. Enable airplane mode to terminate all network connections, including the VPN.
  3. Disable airplane mode to allow the VPN and other connections to reconnect, ideally within the VPN tunnel.

  Note: This method is not foolproof, as some connections may still bypass the VPN upon reconnection.

• Always-On VPN (Enterprise Only):Apple’s Always-On VPN feature, available only on supervised devices enrolled in Mobile Device Management (MDM), ensures all traffic routes through the VPN. This is not viable for most third-party VPN applications or individual users.
• Kill Switch Activation:Since iOS 14, Apple has provided developers with a kill switch feature to block non-VPN traffic. Ensure your VPN provider has implemented this in their app, as it significantly reduces bypass risks.

Choosing a Reliable VPN

When selecting a VPN to mitigate this vulnerability, prioritize services with robust security features. Key attributes include:

• Support for modern protocols like WireGuard or IKEv2.
• A no-logs policy to protect user privacy.
• Features like dedicated IPs and unlimited bandwidth for consistent performance.

For a detailed comparison of plans offering these features, refer to the table below:

All plans include: Dedicated IP, Port Forwarding, Unlimited Bandwidth, No-logs Policy, WireGuard & IKEv2. Learn more about these features at our features page.

Persistent Challenges and Apple’s Response

Apple has acknowledged this vulnerability but has stated that certain Apple services bypassing VPNs is “expected behavior.” Fixes introduced in iOS updates (up to iOS 16) have been incomplete, with some DNS queries and long-lived connections still escaping the VPN tunnel. Apple restricts Always-On VPN to enterprise-managed devices, limiting its accessibility for individual users.

Current Status

As of the latest reports, the issue persists across iOS versions, including 13.5, 13.6, 13.7, and 16. IT professionals should monitor Apple’s release notes for updates addressing this vulnerability and test VPN behavior after each iOS update.

Best Practices for Advanced Users

To enhance security while awaiting a permanent fix:

• Regularly test VPN connections using packet capture tools to identify bypass traffic.
• Use VPN services with a kill switch enabled to block non-VPN traffic.
• Avoid relying on VPNs for sensitive activities on public Wi-Fi until the issue is resolved.
• Check your VPN provider’s client area for updates on iOS compatibility at our client area.

This vulnerability underscores the importance of understanding VPN limitations on iOS. By implementing the outlined mitigations and selecting a robust VPN service, IT professionals can better protect their networks and users.