In light of the recent TunnelVision vulnerability I wanted to share a simple firewall that I wrote for wireguard VPNs.
https://codeberg.org/xabadak/wg-lockdown
If you use a fancy official VPN client from Mullvad, PIA, etc, you won’t need this since most clients already have a kill switch built in (also called Lockdown Mode in Mullvad). This is if you use a barebones wireguard VPN like me, or if your VPN client has a poorly-designed kill switch (like NordVPN, more info here).
A firewall should mitigate the vulnerability, though it does create a side-channel that can be exploited in extremely unlikely circumstances, so a better solution would be to use network namespaces (more info here). Unfortunately I’m a noob and I couldn’t find any scripts or tools to do it that way.
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The vulnerability doesn’t work on LinuxUnfortunately Linux is affected https://github.com/leviathansecurity/TunnelVision
TunnelVision appears to work on any operating system that has a DHCP client that implements support for DHCP option 121. Most modern operating systems support this such as Linux, Windows, iOS and MacOS. Notably, Android does not appear to have support for option 121 and remains unaffected.
A fix is available on Linux when configuring the VPN users host to utilize network namespaces.
I read the Arstechnica article too where they say Linux isn’t affected then link to the researchers video where they show Linux being affected…
Oh. It doesn’t work with WireGuard then. It probably works with garbage. Thank you.
I am afraid you are still a bit misled; WireGuard is exactly what they use for the demo video. In general the underlying protocol does not matter, since the vulnerability is about telling the system to direct the packages to the attacker, completely bypassing the VPN.
That “vulnerability” seems more like a case of “people who use hostile networks have not considered which features that work as designed should be disabled in their use case”.
Does it matter?
This is a vulnerability anyway and we should be take care of.
It does matter if people now advocate to routinely disable useful features by default because they are a problem for their particular use case.
what features are you talking about?
Using untrusted networks is quite common, like coffee shop wifi or airport wifi.
You’re still right in 99% of all use cases.
Nobody operates VPNs for privacy in split tunnel. So everyone running Linux that would be concerned about this is unaffected.
I thought TunnelVision applies to all VPN users that don’t use firewall / network namespaces
It doesn’t apply to Linux unless you do split tunnel, which no commercial VPN configs use, because it doesn’t make sense to
why is a split tunnel relevant? I thought all VPNs are vulnerable unless they use a firewall like I do, or network namespaces.
At least the way I understand it, a normal VPN redirects your internet traffic to instead go through a virtual network interface, which then encrypts and sends your traffic through the VPN. This attack uses a malicious DHCP server to inject routes into your system, redirecting traffic to the attacker instead of towards the virtual network interface.
A separate routing table that takes precedence over the one modified by DHCP should works as well I think. Oh, and of course you have to use a vpn that forces its own nameserver or set one manually to prevent redirections.
