jtesta
Update Hardening guide (Terrapin)
The Hardening guide needs to be updated to remove [email protected], that is - if removal of that cipher is the suggested solution for the time being.
https://www.ssh-audit.com/hardening_guides.html
I can't see any reference for the removal of [email protected] in the OpenSSH release notes, @keteague why do you think it is necessary to remove it?
According to the site for the Terrapin Attack noted in the subject, from the first entry in the FAQ: https://terrapin-attack.com/index.html#question-answer
If you feel uncomfortable waiting for your SSH implementation to provide a patch, you can workaround this vulnerability by temporarily disabling the affected [email protected] encryption and [email protected] MAC algorithms in the configuration of your SSH server (or client), and use unaffected algorithms like AES-GCM instead.
The floating quick patch for this is to place the following in a file in the /etc/ssh/sshd_config.d/ folder:
Ciphers [email protected]
MACs -*[email protected]
@keteague : it seems that all supported platforms issued patches to include the [email protected] key exchange marker. This marker signifies that the Terrapin vulnerability is fixed (that is, as long as all clients also support it). Hence, I think its generally safe enough to keep the chacha20-poly1305 cipher enabled, though for any admins wanting to disable it in their environment, they can certainly do so. In that case, they can also create a custom policy based on their updated config as well.
I suppose I'll mark this issue as complete, as no other replies have come after almost a week.