VPNs are critical tools for online privacy and security. However, recent research by Leviathan Security has uncovered a new technique known as TunnelVision that can bypass VPN encryption without breaking it. TunnelVision exploits DHCP option 121 configurations, enabling an attacker to direct traffic outside of the VPN tunnel. This technique may have been possible since 2002, but it does not compromise VPN encryption and does not violate any of the fundamental security properties of VPNs.

Not all operating systems are equally susceptible to TunnelVision. Android is not vulnerable due to its different handling of DHCP options, while Windows, Linux, macOS, and iOS are all vulnerable.

For VPN users, the situation may seem daunting. However, in the absence of comprehensive fixes from VPN providers, there are practical steps that users can take to mitigate the risk posed by TunnelVision.

Mitigate and enhance your security:

1. Configure Firewall Rules: Users can configure firewall rules on their devices to drop outbound packets that attempt to bypass the VPN tunnel. This proactive measure adds an extra layer of protection against potential TunnelVision attacks.

2. Run VPN on a Virtual Machine: Running a VPN within a virtual machine with a network adapter, not in bridged mode can isolate VPN traffic from the underlying host system, making it more resilient to routing manipulation.

3. Connect to VPN on Cellular Data: Leveraging cellular data connections instead of Wi-Fi networks can mitigate the risk of TunnelVision attacks, as cellular networks typically do not rely on DHCP for configuration.

Conclusion:

TunnelVision presents a potential threat to VPN security, but it is not an insurmountable one. By understanding the underlying vulnerabilities and taking proactive measures to address them, users can continue to enjoy the benefits of VPNs while minimizing the risk of exploitation. However, it is crucial for VPN providers to step up and prioritize the implementation of robust security features to ensure the integrity of their services in the face of evolving threats such as TunnelVision.

References:

TunnelVision (CVE-2024-3661) https://www.leviathansecurity.com/blog/tunnelvision

NVD https://nvd.nist.gov/vuln/detail/CVE-2024-3661

DHCP option 121 https://datatracker.ietf.org/doc/html/rfc3442