TunnelCrack: Widespread design flaws in VPN clients
tunnelcrack.mathyvanhoef.com
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We present two widespread design flaws in VPN client. These can be abused to make a victim leak traffic in plaintext outside the protected VPN tunnel.

Tests indicate that every VPN product is vulnerable on at least one device, the researchers say. VPNs for iPhones, iPads, MacBooks, and macOS are extremely likely to be vulnerable, that a majority of VPNs on Windows and Linux are vulnerable, and that Android is the most secure with roughly one-quarter of VPN apps being vulnerable.

I wish they’d been more specific in the general description; this is a local routing attack that can be applied against clients of public VPN services.

For a moment I was worried about my personal VPN, which is not configured in a way that this abuse could happen.

@jet@hackertalks.com
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7
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1Y

Traffic leaking has always been a concern when sitting up a VPN or any network infrastructure. Especially when you’re dealing with sensitive data. These concerns are old, and not sensational, new traffic leak discovered in local routing configuration of some VPN clients.

The truly paranoid would have a always-on VPN, no traffic may go outside the VPN, defense in depth. A VM that can only talk to the VPN endpoint. You could use qubes to configure something bulletproof, mullvad even has an article explaining how to do this yourself.

Just out of good hygiene I have leak checks in my computing systems. If they succeed it shuts everything down. Like if you open a browser it checks your external facing IP address. Imagine it’s pretty common for people.

Em Adespoton
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31Y

Very few people have functional leak checking set up; personally, I think it should be a built-in OS level function.

@jet@hackertalks.com
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21Y

It would be nice. But it’s a hard problem to solve. To figure out somebody’s intense by running a VPN or having certain IP routing rules.

https://mullvad.net/en/help/qubes-os-4-and-mullvad-vpn/

I do like in this guy day emphasize setting up routing rules so the VPN can only route traffic to VPN endpoints. It’s a nice fail safe

@jet@hackertalks.com
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901Y
"Both attacks manipulate the victim's routing table to trick the victim into sending traffic outside the protected VPN tunnel, allowing an adversary to read and intercept transmitted traffic. "

I hate clickbait titles. A better title for this would be, local routing attack may expose some VPN traffic. It’s pretty esoteric, not seen in the wild, and requires your adversary to have control of your local network and exposes traffic of a very particular kind. These panic inducing headlines are just annoying and they desensitize us

Cynber
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51Y

have control of your local network

traffic of a particular kind

Could you give an example of what this looks like? I’m sure I’ll have friends sending me similar articles / YouTube videos. Would be nice to have a simple and accurate analogy

Well, depending what your local network is, this could be a problem. I imagine cellphone networks i.e. could be affected.

ADHDefy
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111Y

It’s too bad they don’t offer a complete list of known patched VPNs. They just give like 5 example ones. It’d be really helpful to know if my service has patched already or not.

unsure about patches applied since writing, but near the ending pages in the original paper theres a more exhaustive list of the state of vpns

https://mullvad.net/en/blog/2023/8/9/response-to-tunnelcrack-vulnerability-disclosure/ is Mullvad’s response to this topic. TLDR not a concern other than possibly for IOS.

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