25 Aug 2022 Cyber Networking

Fix SSH WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED

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Run `ssh-keygen -R hostname` to remove only the outdated key for the specific host from your known_hosts file, then reconnect and accept the new fingerprint. Alternatively, open `~/.ssh/known_hosts`, find the line matching the host, delete it manually, and save. This avoids removing all trusted hosts while resolving the mismatch error immediately.

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1.
What it is
This article explains how to resolve the SSH warning that appears when a remote server's fingerprint has changed, indicating a potential security issue or server change.
2.
Why it matters
This error blocks SSH connections and needs immediate attention since it could indicate a security breach or legitimate server update that requires user verification.
3.
Key takeaway
The quickest fix is deleting the known_hosts file, though this removes all stored server fingerprints and requires re-accepting them.

~1 min read

If the fingerprint of your remote host changes you will see the following error message appear:

 ~ % ssh -i "mykey.pem" [email protected]
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    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 ED25519 key sent by the remote host is
SHA256:S60CvpE17ri+E594StxXBQcNIrga4Nb7uX4s7BPr3dw.
Please contact your system administrator.
Add correct host key in /Users/user_id/.ssh/known_hosts to get rid of this message.
Offending ED25519 key in /Users/user_id/.ssh/known_hosts:2
Host key for my_host.af-south-1.compute.amazonaws.com has changed and you have requested strict checking.
Host key verification failed.

There are many ways to fix this. The easiest of which is simply to delete your “known_hosts” file. This will mean you just need to accept new finger prints on all your SSH hosts. Yes, this is very lazy…

rm ~/.ssh/known_hosts