[rahimnathwani]

> can cause traffic to go over those routes instead of the VPN

AIUI the vulnerability is more about forcing traffic via a specific interface than it is about the setting the route. The host's routing table contains at least these fields:

A) destination (IP or subnet)

B) gateway (aka route, aka next hop)

C) interface

The article says that when the route is set using DHCP Option 21, the interface field is set to the interface on which the DHCP response was received. So, if I've understood the article correctly, even if the route/gateway address is correct and not malicious, the host will send out packets for that destination via the regular (wifi or ethernet) interface, instead of the VPN interface.

Imagine a coffee shop scenario: a malicious DHCP server responds to your DHCP request. It includes Option 121, making certain traffic go to the 10.0.0.1 (the coffee shop router address). Now, even though that gateway isn't malicious, the fact that the traffic is now going over the wifi interface instead of VPN, means someone can snoop on it.