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.
The ability to set static routes via DHCP server or for that matter the ability to remote boot systems via DHCP server which has similar problems if you can’t trust the DHCP server.
I see what you mean now. I wouldn’t advocate for people to disable DHCP features either. It should be the VPN provider’s responsibility to provide a proper VPN client that mitigates attacks like these.