jeffwNovel attack against virtually all VPN apps neuters their entire purpose
Postmortal_PopSo I gave the article a glance and it’s a bit beyond me can someone give me an eli5?
BricriuMy understanding is that if you run a rogue discoverable DHCP server in a local network with a particular set of options set and hyper-specific routing rules, you can clobber the routing rules set by the VPN software on any non-Android device, and route all traffic from those devices through arbitrary midpoints that you control.
But IANANE (I am not a network engineer) so please correct my misinterpretations.
this implies physical access or at least access within the network?
SzethFriendOfNimiKeeping in mind that may mean that somebody like a cellular provider could do so. Since your local network in that context would be them.
Exactly. And if your ISP or cellular provider wants, or is forced, to gather information about your internet activities, they can almost certainly find a way. The cheap consumer-grade VPN services most of us use just prevent casual or automated observers from easily detecting your device’s IP address. For most people that just want to torrent casually or use public wifi, it’s enough.
Or to watch porn in one of the states that block porn.
Transient PunkThat, or the ability to spoof it
lemmyngIt has implications on the effectiveness of VPNs on public networks.
Or I expect compromise of anything on the LAN that can create a rogue DNS server that can override the routing table.
But I might be missing something
(obligatory I’m not a network surgeon this is likely not perfectly correct)
The article mentions network interfaces, DHCP and gateways so real quick: a network interface usually represents a physical connection to a network, like an Ethernet port or a WiFi card. DHCP is a protocol that auto configured network routes and addresses once a physical connection is established, like when you jack in via an ethernet cable, it tells you the IP address you should go by, the range of IP address on the network you’ve connected to, where you can resolve domain names to IP addresses. It also tells you the address of a default gateway to route traffic to, if you’re trying to reach something outside of this network.
You can have more than one set of this configuration. Your wired network might tell you that your an address is 10.0.0.34, anything that starts with 10.0.0. is local, and to talk to 10.0.0.254 if you’re trying to get to anything else. If at the same time you also connect to a wireless network, that might tell you that your address is 192.168.0.69, 192.168.0.* is your local network, and 192.168.0.254 is your gateway out. Now your computer wants to talk to 4.2.2.2. Should it use the wireless interface and go via 192.168.0.254? or the wired one and use 10.0.0.254? Your os has a routing table that includes both of those routes, and based on the precedence of the entries in it, it’ll pick one.
VPN software usually works by creating a network interface on your computer, similar to an interface to a WiFi card, but virtual. It then asks the OS to route all network traffic, through the new interface it created. Except of course traffic from the VPN software, because that still needs to get out to the VPN provider (let’s say, at 1.3.3.7) via real Internet.
So if you’re following along at time, your routing table at this point might look like this:
- traffic to 1.3.3.7 should go to 10.0.0.254 via the wired interface
- all traffic should go to the VPN interface
- traffic to 10.0.0.* should go to the wired interface
- all traffic should go to 10.0.0.254 via the wired interface
- traffic to 192.168.0.* should go to the wireless interface
- all traffic should go to 192.168.0.254 via the wireless interface
whenever your os wants to send network packets, it’ll go down this list of rules until one applies. With that VPN turned on, most of the time, only those two first rules will ever apply.
If I’m reading the article correctly, what this attack does, is run a DHCP server, that when handing out routing rules, will send one with a flag that causes, for example, the last two rules to be placed at the top of the list instead of the bottom. Your VPN will still be on, the configuration it’s requested the OS to make would still be in place, and yet all your traffic will be routed out to this insecure wireless network that’s somehow set itself as the priority route over anything else.
Thank you network nurse
That actually lays it out incredibly well for me. So in practice, what would I need to look out for as a wired desktop Ubuntu user with mullvad? It’s sounding like this is going to be an issue on public networks, is this something my isp can do to me at home?
It all depends on how much you trust the devices on your LAN. So your ISP can’t do anything unless they own and control your router, since that is on your LAN. So one concern might be if you connect your PC to coffee shop wifi, since all other devices in the shop are on the same LAN, not to mention the coffee shop owns the wifi router and can also perform the attack. Another concern might be if a family member in your house has a device that got hacked, then all devices in your house are vulnerable.
verity_kindleThank you, you are a surgeon of charity
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.
RimuNo - 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:
By pushing routes that are more specific than a /0 CIDR range that most VPNs use, we can make routing rules that have a higher priority than the routes for the virtual interface the VPN creates.
Most traffic gets sent through a VPN only because of the 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 address space, they would effectively override that default gateway. I believe that’s the scenario described in the article.
Max-PMost 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.
I use option 121 as part of my work, though I am not an expert on DHCP. This attack does make sense to me and it would be hard to work around given the legitimate uses for that option.
What are the legitimate uses of option 121?
Adding routes for other thing on the network the clients can reach directly and remove some load from the router. For example, reaching another office location through a tunnel, you can add a route to 10.2.0.0/16 via 10.1.0.4 and the clients will direct the traffic directly at the appropriate gateway.
Arguably one should design the network such that this is not necessary but it’s useful.
To be fair, any proper VPN setup that only relies on the routing table like this is flawed to begin with.
If the VPN program dies or the network interface disappears, the routes are removed aswell, allowing traffic to leave the machine without the VPN.
So it is already a good practice to block traffic where it shouldnt go (or even better, only allowing it where it should).
If the VPN program dies or the network interface disappears, the routes are removed aswell, allowing traffic to leave the machine without the VPN.
So it is already a good practice to block traffic where it shouldnt go (or even better, only allowing it where it should).
A good reason to never trust in shady VPNs.
This isn’t a problem with the VPN, as the article says.
But that involves clicking the link and reading.
We don’t do that here, we just get angry.
According to the article i suppose the same technique can be implemented by the VPN provider, but if you like to continue using shady VPNs it’s not my business… good luck!! 👍✌️.
A shady vpn provider wouldn’t need to use this technique at all dumbass.
Keep crying LMAO…
Why would someone cry because you’re wrong?
adam_y“There are no ways to prevent such attacks except when the user’s VPN runs on Linux or Android.”
So there are ways.
Common Linux w
Not really, Linux is still vulnerable and there is a mitigation but it opens a side channel attack.
This is the way
Hate to rain on the Linux parade here, but didn’t the article say: “There are no ways to prevent such attacks except when the user’s VPN runs on Android.” and that Linux was just as vulnerable as Windows?
you’re replying to a verbatim quote from the article.
I was going from this: (emphasis mine)
Interestingly, 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.
KairuBytePartial context is a bitch.
0xDIt’s not as vulnerable but it still is.
Interestingly, 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.
But in the details this attack is not that bad. E.g. NordVPN and I guess also other VPNs use firewall rules to drop traffic on normal network interfaces.
Their side channel is still routing traffic away from the VPN channel. Then they can observe that there is no traffic and guess that the user either didn’t make requests in that moment or that he wanted to visit a website in the range covered by the route. They can not spy on the traffic.
Also you can not quickly move into a network and apply this attack, as DHCP leases usually last 1 day or at least 1 hour. Only when they expire you can apply the attack (or you force the user to drop from the network, which is easy if they are using WPA2, but only possible by blocking the wifi signal if they are using WPA3)
It is a serious issue and should be mitigated, but not as huge as news articles make it.
You can also use network namespaces on Linux which Wireguard has a nice explanation and walkthrough on, recommending this as part of setting up wg connections. www.wireguard.com/netns/
I saw that but unfortunately it doesn’t detail how to set it up persistently on every boot. And I also haven’t seen anybody using this method, probably because of the lack of tooling around it. For example afaik the official Mullvad client on linux just uses a firewall.
Wait so the vulnerability exists on macos and iphone even though those are based on bsd (right?)
Edit: and also Windows, forgot about Windows
Hilariously enough, Windows users can use WSL to run a Linux VPN (but only applications running in WSL are safe if I understand the attack right)
True, if you neg a linux dev online enough for two years, you can make your entire infrastructure vulnerable to attack
(…) the entire purpose and selling point of VPNs, which is to encapsulate incoming and outgoing Internet traffic in an encrypted tunnel and to cloak the user’s IP address.
No. That is not the entire point of a VPN. That’s just what a few shady companies are claiming to scam uninformed users into paying for a useless service. The entire point of a VPN is to join a private network (i.e. a network that is not part of the Internet) over the public internet, such as connecting to your company network from home. Hence the name ‘virtual private network’.
There are very little, if any, benefits to using a VPN service to browse the public internet.
Well, for one, using one of those VPN providers has kept DMCA takedown notices away from me or the hosting provider of my seed box. So that is useful.
There are very little, if any, benefits to using a VPN service to browse the public internet.
I’ve run into issues multiple times where a site doesn’t load until I turn on my VPN with an endpoint in the EU
There are very little, if any, benefits to using a VPN service to browse the public internet.
accessing services that are blocked in your region.
that works, but a regular SOCKS proxy should do. for HTTP even a HTTP proxy. many VPN providers offer them too, btw… may help with mitigating this attack vector.
There are very little, if any, benefits to using a VPN service to browse the public internet.
This is why it’s often best to just avoid the comments completely
vext01Come to think of it, why do they even call this use case a VPN? I’d call that a proxy.
there are no ways to prevent such attacks except when the user’s VPN runs on Linux or Android.
So . . . unix? Everything-but-Windows?
Maybe it affects BSD and MacOS.
It also can affect some Linux systems based on configuration. Android doesn’t implement the exploited standard at all and is always immune.
Everything-but-Windows?
No. Any device that implements a certain DHCP feature is vulnerable. Linux doesn’t support it, because the feature is only useful for home computing/office workstations where Linux is rarely used. And Android doesn’t support it because it inherited the Linux network stack.
ElderWendigobecause most Linux systems don’t even use DHCP
This is the dumbest thing I’ve heard all day.
most Linux systems don’t even use DHCP
WTF are you smoking? WTF is wrong with you that you think such a dumb claim would go unscrutinized? I would play Russian roulette on the chances of a random Linux installation on a random network talking DHCP.