5

I bought a proxy service. In order to setup my browser I have to establish a SSH tunnel to their server. Since I do not want to observe it permanently, I want to setup autossh for it.

But what I wonder: If the server of the proxy service is hacked or if another customer, who also connects to the SSH tunnel, is infected: Can they damage my machine in any way? Steal data, connect to my computer or what ever...

Is this a legitimate worry or totally impossible?

4

There were such examples if you were using X11 forwarding, for example as described in this report:

https://thejh.net/written-stuff/openssh-6.8-xsecurity

Similar issue was published many years ago:

http://www.giac.org/paper/gcih/571/x11-forwarding-ssh-considered-harmful/104780

All these should be fixed now, but using -X forwarding to untrusted machines can still be potentially dangerous.

2

Can someone crawl back down your SSH connection and infect your computer? No. Can they see there's a connection from your external IP address then scan/enumerate/potentially exploit your gateway (e.g. router)? Yes.

What you should really be concerned with is if the proxy provider is worth trusting with your web traffic. By proxying your traffic through their network you give them direct access to sniff your traffic, whether it's in the fine print or not. The traffic will be encapsulated by the SSH tunnel and obfuscated from your ISP, but once it is egressing from the proxy provider it's fair game.

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