| Summary: | Confusing error "host key ... has changed" when connecting to a server not offering matching host key types | ||||||
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| Product: | Portable OpenSSH | Reporter: | jatjasjem | ||||
| Component: | ssh | Assignee: | Damien Miller <djm> | ||||
| Status: | CLOSED FIXED | ||||||
| Severity: | minor | CC: | djm, dtucker | ||||
| Priority: | P5 | ||||||
| Version: | 7.9p1 | ||||||
| Hardware: | ARM64 | ||||||
| OS: | Linux | ||||||
| Bug Depends on: | |||||||
| Bug Blocks: | 3217 | ||||||
| Attachments: |
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Created attachment 3455 [details]
Do not prefix "host key changed" message with potentially incorrect key type
Yes, the key type in that error should not be there.
This has been committed and will be in OpenSSH 8.5 close bugs that were resolved in OpenSSH 8.5 release cycle |
I'm trying to connect to a server that I previously connected to. The last time I connected to it, ssh used its ECDSA key for host verification. This is the only key in my known hosts file: $ cat ~/.ssh/known_hosts | awk '{print $2}' | uniq ecdsa-sha2-nistp256 The server is no longer offering this key. This is what I get when I try to connect now: $ ssh user@host -p 23 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has just been changed. The fingerprint for the RSA key sent by the remote host is SHA256:VzEhMh3aw2lqAsZSdLbYJAhwW4yIgUxCRotrMoWqzT9. Please contact your system administrator. Add correct host key in /home/user/.ssh/known_hosts to get rid of this message. Offending ECDSA key in /home/user/.ssh/known_hosts:1 remove with: ssh-keygen -f "/home/user/.ssh/known_hosts" -R "[host]:23" RSA host key for [host]:23 has changed and you have requested strict checking. Host key verification failed. I am expecting to get this warning, but the penultimate line sounds wrong to me. From the point of view of ssh, "RSA host key" shouldn't appear changed; it didn't know anything about it at all. In fact, the actual RSA key on the server never changed. What changed was the type of key offered by the server. I think the error message should reflect that. To reproduce, run /usr/sbin/sshd -ddd -p 23 -oHostKeyAlgorithms=ecdsa-sha2-nistp256 Connect to let ssh remember the key, then run /usr/sbin/sshd -ddd -p 23 -oHostKeyAlgorithms=rsa-sha2-256 Connect again and observe the error