Really interesting. Dhcp optional routes overriding VPN tunnel routing rules.
The researchers believe it affects all VPN applications when they’re connected to a hostile network and that there are no ways to prevent such attacks except when the user’s VPN runs on Linux or Android.
Once again, Linux with a win!
Partially. The summary isn’t quite in line with the detail:
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 disagree with one of their points
Network firewalls can also be configured to deny inbound and outbound traffic to and from the physical interface. This remedy is problematic for two reasons: (1) a VPN user connecting to an untrusted network has no ability to control the firewall and (2) it opens the same side channel present with the Linux mitigation.
Sure, they can’t control the network firewall, but why would you do that when you can change your local firewall? Set an iptables rule to drop all traffic going out the physical interface that isn’t destined for the VPN server. I’m 70% sure some vpn clients do this automatically.
Why doesn’t my internet look like that stock image tunnel of 1 and 0?
Dang option 121.
I told him 120 options was enough, but he just had to keep adding options.
Any vpn solution that uses a TCP/IP shim in full tunnel mode will ignore option 121 or any other routing options (static routes, etc). Most corporate VPNs like Global Protect/Cisco Any Connect, Appgate, etc will enforce full-tunnel. Any user who is using a VPN for privacy reasons should also use a full tunnel as well especially when connecting to an untrusted networks.