this post was submitted on 06 May 2024
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So if they are changing routes by using DHCP options, perhaps this could be exploited by telecom insiders when you are using mobile data, because your mobile data IP could be assigned by a DHCP server on the telecom network. If you're at home on wifi, then you can control your own DHCP server to prevent that.
No - the VPN provider has another DHCP server for use 'inside' the VPN.
Except this bypasses that I believe.
The attack vector described in the article uses the VPN client machine's host network, i.e. the local network the device is attached to. They don't discuss the DHCP server of the VPN provider.
Read this part more carefully:
Most traffic gets sent through a VPN only because of a default gateway (set by the VPN) in the client's routing table. If the client's ISP were to have their DHCP server set one or more specific routes that are broad enough to cover most of the global address space, they would effectively override that default gateway. I believe that's the scenario described in the article.
Note that the "ISP" here could be a mobile operator, an internet cafe, an airport, someone running a wifi access point that looks like the airport's, or a guest on the same local network running an unauthorized DHCP server.
Most VPN providers don't use DHCP. OpenVPN emulates and hooks DHCP requests client-side to hand the OS the IP it got over the OpenVPN protocol in a more standard way (unless you use Layer 2 tunnels which VPN providers don't because it's useless for that use case). WireGuard doesn't support DHCP at all and it always comes from configuration.
The attack vector here seems to be public WiFi like coffee shops, airports, hotels and whatnot. The places you kinda do want to use a VPN.
On those, if they're not configured well such as coffee shops using consumer grade WiFi routers, an attacker on the same WiFi can respond to the DHCP request faster than the router or do an ARP spoof attack. The attacker can proxy the DHCP request to make sure you get a valid IP but add extra routes on top.