They have posted on Reddit that if you have kill switch and wireguard you are safe on every platform except Linux. A fix is being worked on for linux, no ETA.
Hi!
Our engineers have conducted a thorough analysis of this threat, reconstructed it experimentally, and tested it on Proton VPN.
We concluded that:
the attack can only be carried out if the local network itself is compromised
our Windows and Android apps are fully protected against it
for iOS and macOS apps, you are completely protected from this as long as you're using a Kill Switch and a WireGuard-based protocol (our apps use WireGuard by default, and if a user wants to use something other than WireGuard derivates, they'd have to manually set it up). Note that Stealth, WireGuard TCP, and our Smart protocol on iOS/macOS are all WireGuard-based.
for our Linux app, we're working on a fix that would provide full protection against it.
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.
Interestingly, Android is the only operating system that fully immunizes VPN apps from the attack because it doesn't implement option 121. For all other OSes, there are no complete fixes. When apps run on Linux there’s a setting that minimizes the effects, but even then TunnelVision can be used to exploit a side channel that can be used to de-anonymize destination traffic and perform targeted denial-of-service attacks.
I did not look into that setting that minimises the effect but from the way it's written it sounds like this isn't used by default, so by default you're still vulnerable. Add even if it's on, there's still a side vulnerability.
well, im not as im not using interfaces that are affected by the vulnerability (im using named, containerized network interfaces), but i appreciate the info!
it was initially reported as 'linux & android' were not affected.
i stand by my statement that this isnt about the VPN provider, its a client problem. so the question about Proton is moot.
I think by client you mean the device and operating system, which is correct to my understanding, but it's confusing because 'client' can also mean the VPN client software which is often supplied by the VPN provider, and that's what I first think when you say client. So with that in mind it sounds like you're saying "it's not about the VPN but the VPN software" which obviously comes from the same provider.
I have not looked into it so you probably understand this more than I, but from the sound of it the VPN software can be built to detect, prevent or counteract the exploit even on affected systems? In which case, even though it's an environment issue it can still be resolved by the VPN provider.
Yes, client network configuration problem, across all platforms.
I'm actually wrong saying "all VPN alternatives" - because this goes even further than that. It can be an issue for all network interfaces, regardless of VPN or not.
That we haven't heard anything from proton regarding this vulnerability is not a good sign. Article came out on May 6th and proton has only published basic privacy guides.