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points

by raggi5 days ago |

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by sph4 days ago|

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Acronyms are supposed to be capitalised. I do not belive you are talking about the soy product.

https://en.wikipedia.org/wiki/Man-in-the-middle_attack

https://en.wikipedia.org/wiki/Trust_on_first_use

by kro5 days ago|

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I understand that most people don't use it and indeed rely on tofu, but the statement is not absolutely correct.

ssh server keys can be authenticated using (the DNSSEC "CA" system and) SSHFP, and it's possible to setup a signing CA for the host key (similar to ssh certificates, however not applicable for foreign servers). And of course, the fingerprint could be advertised out of band e.g. on the homepage with tls

by raggi4 days ago|

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sshfp is not PKI. It's an option and it is off by default in ssh(1). In practice no one actually deploys it, exe.dev, terminal.shop, jobs.{whoever.com}, etc. I've yet to see an in the wild deployment. The aforementioned sites let you perform electronic payment transactions over ssh without it, which is probably a PCI violation tbh, but auditors aren't good enough.

webpki is on by default.

by rvz4 days ago|

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Agreed. Amid all this hype, once again we continue to see such disregard for basic security implications and using ssh outside it's intended use-case; especially sshing into random servers.

Now we wait for the discovery of an RCE, key leakage vulnerability or a security bypass that leads to a trivial mitm attack to magnify why ssh apps make no sense security wise.

by tptacek4 days ago|

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SSH does in fact have a PKI, just not a global one. Large-fleet SSH installs all tend to use certificate authorities, for this reason (and to simplify SSO).

by raggi3 days ago|

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Fair!

When I last harassed Crawshaw about this and we discussed bits, he submitted https://github.com/C2SP/C2SP/blob/main/well-known-ssh-hosts....

Unfortunately neither of us has taken time (AFAIK) to go back and implement it anywhere.

by tptacek3 days ago|

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I don't understand the impulse behind these things --- this is a bootstrap mechanism for a global PKI for SSH. But cold introductions to SSH hosts (that is, first connections to hosts you have no business or technical relationship with) virtually never happen. What problem does it solve?

by raggi3 days ago|

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When you see people advertising a coffee shop at a conference and people TOFU'ing on conference wifi then plugging in credit card numbers, the picture gets a little more clear.

by tptacek2 days ago|

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Right, I mean, I see the problem for browsers! Just not for SSH servers. (Capturing sessions like this used to be a contest at Usenix Security).

by raggi2 days ago|

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So really the trend I'm talking about here is people turning SSH into a browser, hosting apps behind SSH that expect a much higher volume of TOFU happening, which is a departure from the "first time i setup my vps" kind of case.

Honestly at this point I'd be kind of happy if we could just use an x.509 cert from a webpki acme provider in the sshd and be done with it, for the host identity part.

by edmccard2 days ago|

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Do people at conferences buy coffee by SSH'ing into coffee shop servers?

by raggi2 days ago|

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i've seen it, so the answer is non-zero

by pzacik5 days ago|

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Yes, but what exactly would an attacker achieve by doing mitm here?

by raggi4 days ago|

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here, less than most, but look for ssh agents

on terminal.shop, steal credit cards on jobs endpoints, perform identity theft on exe.dev, whatever you put on there