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I upgraded my Mac to Monterey the other day and all of a sudden all of my SSH connections would not work any more. After some digging, I came across a solution

I upgraded my Mac to Monterey the other day and all of a sudden all of my SSH connections would not work any more. After some digging, I came across a solution where adding Host hostnameOrIPaddress HostKeyAlgorithms +ssh-rsa PubKeyAcceptedKeyTypes +ssh-rsa to ~/.ssh/config fixed the issue. I'm wondering if doing this makes me more vulnerable? Or is bad practice somehow? NB: using iTerm2 3.5.0beta9 and Oh My Zsh master (a1c54e0).

hartmel 4y ago
Edit: my bad, +ssh-rsa refers to a signature algorithm using SHA1, which should not be used anymore. Target server host keys should be renewed, as told by riolu, thanks to him for pointing it. On debian-like, remove host keys and run dpkg-configure openssh-server. On redhat-like, remove host keys and restart sshd. --------------------------------------------- Not vulnerable, not a bad practice. Newer algorithms are faster (in practice not perceptible, people usually don't need state of the art performance for SSH connections), with smaller keys and probably better algorithms (not subject to side channel attacks, which are still hard to abuse) but RSA is not broken. It may be in a few years with quantum computing but it's still far to be sure. https://www.schneier.com/blog/archives/2021/03/no-rsa-is-not-broken.html https://www.schneier.com/blog/archives/2021/03/no-rsa-is-not... updated last december. No need to rekey all accounts or servers, just switch to ecdsa or ed25519 progressively.
- josephcsible 4y ago
  That change isn't actually about RSA vs. ECC. It's about SHA-1 vs. SHA-2. The default configuration still supports using your existing RSA keys, but with a different hashing algorithm (with the options rsa-sha2-256 and rsa-sha2-512). That configuration change allows use of SHA-1 to continue.
riolu 4y ago
That isn't even remotely related the post and Monterey is over a year old. The systems you are trying to SSH to are using outdated host keys, you need to actually update to get security fixes, it will regenerate host keys. You shouldn't be worried about this CVE, it sounds like you have quite a few years of CVE's you've neglected to patch anyways.
- josephcsible 4y ago
  > The systems you are trying to SSH to are using outdated host keys, you need to actually update to get security fixes, it will regenerate host keys. No you don't. rsa-sha2-256 and rsa-sha2-512 are still enabled by default and can use the same key.
- obituary_latte 4y ago
  The reason it triggered my question is they had to do something similar to get the exploit to work (add +ssh-rsa to putty). Thanks, though, for the thoughtful reply.
deleted 4y ago
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hartmel 4y ago

Edit: my bad, +ssh-rsa refers to a signature algorithm using SHA1, which should not be used anymore. Target server host keys should be renewed, as told by riolu, thanks to him for pointing it. On debian-like, remove host keys and run dpkg-configure openssh-server. On redhat-like, remove host keys and restart sshd. --------------------------------------------- Not vulnerable, not a bad practice. Newer algorithms are faster (in practice not perceptible, people usually don't need state of the art performance for SSH connections), with smaller keys and probably better algorithms (not subject to side channel attacks, which are still hard to abuse) but RSA is not broken. It may be in a few years with quantum computing but it's still far to be sure. https://www.schneier.com/blog/archives/2021/03/no-rsa-is-not-broken.html https://www.schneier.com/blog/archives/2021/03/no-rsa-is-not... updated last december. No need to rekey all accounts or servers, just switch to ecdsa or ed25519 progressively.

josephcsible 4y ago
That change isn't actually about RSA vs. ECC. It's about SHA-1 vs. SHA-2. The default configuration still supports using your existing RSA keys, but with a different hashing algorithm (with the options rsa-sha2-256 and rsa-sha2-512). That configuration change allows use of SHA-1 to continue.

riolu 4y ago

That isn't even remotely related the post and Monterey is over a year old. The systems you are trying to SSH to are using outdated host keys, you need to actually update to get security fixes, it will regenerate host keys. You shouldn't be worried about this CVE, it sounds like you have quite a few years of CVE's you've neglected to patch anyways.

josephcsible 4y ago
> The systems you are trying to SSH to are using outdated host keys, you need to actually update to get security fixes, it will regenerate host keys. No you don't. rsa-sha2-256 and rsa-sha2-512 are still enabled by default and can use the same key.
obituary_latte 4y ago
The reason it triggered my question is they had to do something similar to get the exploit to work (add +ssh-rsa to putty). Thanks, though, for the thoughtful reply.

deleted 4y ago

[deleted]