Evaluating the impact of TunnelVision

We evaluated the impact of the latest TunnelVision attack (CVE-2024-3661) and have found it to be very similar to TunnelCrack LocalNet (CVE-2023-36672 and CVE-2023-35838).

We have determined that from a security and privacy standpoint in relation to the Mullvad VPN app they are virtually identical. Both attacks rely on the attacker being on the same local network as the victim, and in one way or another being able to act as the victim's DHCP server and tell the victim that some public IP range(s) should be routed via the attacker instead of via the VPN tunnel.

The desktop versions (Windows, macOS and Linux) of Mullvad's VPN app have firewall rules in place to block any traffic to public IPs outside the VPN tunnel. These effectively prevent both LocalNet and TunnelVision from allowing the attacker to get hold of plaintext traffic from the victim.

Android is not vulnerable to TunnelVision simply because it does not implement DHCP option 121, as explained in the original article about TunnelVision.

iOS is unfortunately vulnerable to TunnelVision, for the same reason it is vulnerable to LocalNet, as we outlined in our blog post about TunnelCrack. The fix for TunnelVision is probably the same as for LocalNet, but we have not yet been able to integrate and ship that to production.