How to Resolve the “Host Key Verification Failed” Error in SSH

When working with SSH (Secure Shell), it’s not uncommon to encounter the “Host Key Verification Failed” error. This typically happens when there’s a mismatch between the stored host key for a remote server and the key presented by the server you’re trying to connect to. In this post, we’ll walk through the causes of this error and offer solutions to help you resolve it. Let’s get started by understanding the error itself.

What is the “Host Key Verification Failed” Error?

The “Host Key Verification Failed” error occurs when your SSH client detects a mismatch between the public key of a server and the one stored in your local system. When you first connect to a server via SSH, the server’s public key is saved in a file on your local machine (typically located at ~/.ssh/known_hosts). This key helps verify the identity of the server in future connections. If the server’s key changes, SSH won’t trust the connection and will display this error message.

Possible Causes of the “Host Key Verification Failed” Error

Here are some common reasons this error might occur:

• Server Key Changes: The server’s host key has changed due to a server reinstallation or replacement.

• Man-in-the-Middle Attacks: DNS spoofing or malicious actors intercepting your connection could lead to this error.

• IP or Domain Name Changes: If the server’s IP address or domain name has been modified, the stored key may no longer match.

• Corruption of the known_hosts File: If the known_hosts file becomes corrupted or altered, it can cause mismatches with the stored keys.

Steps to Fix the “Host Key Verification Failed” Error

1. Remove the Old Host Key

If the error is caused by a change in the server’s key, you’ll need to remove the outdated key from your known_hosts file. You can do this manually or use a command to simplify the process.

Manually Edit the known_hosts File

• Open the known_hosts file using a text editor:

  bash

  复制编辑

  nano ~/.ssh/known_hosts


• Locate the line corresponding to the server with the error, delete it, and save the file.

Using ssh-keygen

The ssh-keygen command can also be used to remove the problematic key:

• Find the offending host key with the following command:

  css

  复制编辑

  ssh-keygen -F [hostname]


  Replace [hostname] with the server’s IP address or domain name.

• Remove the key entry for that hostname:

  css

  复制编辑

  ssh-keygen -R [hostname]


  This will delete the key associated with the server.

2. Accept the New Host Key

After removing the old key, reconnect to the server:

You’ll receive a prompt asking if you want to accept the new host key:

Type yes and press Enter. This will add the new host key to your known_hosts file, and the connection will proceed as usual.

3. Check for DNS Spoofing or Man-in-the-Middle Attacks

If you suspect that the change in the host key could be a result of DNS spoofing or a man-in-the-middle attack, it’s essential to verify the server’s authenticity. Contact the server administrator through another secure channel to confirm the server’s new fingerprint before accepting it.

4. Verify the Server’s Host Key

You can verify the server’s key manually using the ssh-keyscan command:

This will print the server’s host key. Compare it with the one provided by the server administrator. If they match, you can add the key to your known_hosts file manually:

This will append the server’s key to your known_hosts file.

Automating Host Key Management

For environments where host keys change frequently, you can automate the process of managing host keys.

1. Using SSH Options

You can bypass host key verification temporarily with the -o StrictHostKeyChecking=no option. However, this is not recommended for regular use due to the security risks it poses:

2. Configuring SSH

For better host key management, you can configure SSH options in your SSH configuration file. Open or create the file at ~/.ssh/config and add the following:

This configuration disables strict host key checking and prevents updates to the known_hosts file for the specified host.

Reinstalling or Regenerating SSH Keys

In rare cases, the error might persist due to corrupted SSH keys or configuration files. Reinstalling or regenerating the SSH keys can help resolve this issue.

1. Regenerate SSH Keys on the Client Side

First, back up your existing SSH keys:

Then, generate a new SSH key pair:

Finally, copy the new public key to the server:

2. Regenerate SSH Keys on the Server Side

Access the server through an alternative method, like console access, and back up the existing SSH keys:

Regenerate the server’s SSH keys:

Restart the SSH service:

Conclusion

The “Host Key Verification Failed” error is a common issue when using SSH, but it can be resolved with a few simple steps. By understanding the causes of this error and following the provided solutions, you can maintain secure and reliable SSH connections to your remote servers. Whether you manually remove the old key, verify the server’s authenticity, or automate host key management, you’ll be able to fix the error and continue working without interruptions.