keyboard interactive authentication with ssh2 server failed

3 min read 01-10-2024

keyboard interactive authentication with ssh2 server failed

When working with secure shell (SSH) protocols, one may encounter various authentication issues. One common error that can arise is the "Keyboard Interactive Authentication with SSH2 Server Failed." This article delves into this issue, offering insights into its causes, how to resolve it, and best practices for smooth SSH authentication.

What is Keyboard Interactive Authentication?

Keyboard Interactive Authentication is an SSH authentication method that allows the server to request additional information, often in the form of prompts that a user must answer. This method can include multifactor authentication (MFA) or other custom prompts which enhance security beyond just the username and password.

Common Causes of Authentication Failure

Several factors can contribute to keyboard interactive authentication failures with an SSH2 server:

Misconfiguration of SSHD: The SSH server may not be configured to accept keyboard-interactive authentication. This is often found in the SSH daemon configuration file (/etc/ssh/sshd_config).
Lack of Required PAM Modules: If the server relies on Pluggable Authentication Modules (PAM) and the necessary PAM modules are not installed or configured correctly, the authentication will fail.
Network Issues: If there are network disruptions, packets may not be sent or received properly, leading to authentication problems.
User Issues: The user credentials may be incorrect, or the user might not have permission to log in.
SSH Client Errors: Sometimes the client configuration or version may not be compatible with the server's settings, leading to failed authentication attempts.

Troubleshooting Steps

Here’s a guide on how to troubleshoot keyboard interactive authentication failures:

1. Check SSH Configuration

Ensure that the server's SSH configuration file (/etc/ssh/sshd_config) has the following settings enabled:

ChallengeResponseAuthentication yes
UsePAM yes

After making changes, restart the SSH service:

sudo systemctl restart sshd

2. Verify PAM Configuration

Check if the necessary PAM modules are installed. In many cases, you need to ensure that the appropriate PAM service files are configured properly in /etc/pam.d/.

3. Test with Verbose Mode

You can use SSH in verbose mode to get more detailed error messages:

ssh -vvv user@hostname

This will give you detailed logs that might help pinpoint the failure.

4. Inspect Logs

Check the server logs for any specific error messages related to authentication. The logs can usually be found in /var/log/auth.log or /var/log/secure.

5. User Credential Verification

Double-check the username and password, ensuring the account is not locked or expired. Use the passwd command to reset the user password if necessary.

Practical Example of a Keyboard Interactive Setup

Here’s a simple setup example using SSH with keyboard interactive authentication.

Step 1: Configure SSH Server

Edit /etc/ssh/sshd_config:

ChallengeResponseAuthentication yes
UsePAM yes

Step 2: Install and Configure PAM Module

If you're using Google Authenticator for MFA, install it using:

sudo apt-get install libpam-google-authenticator

Then, add the following line in your PAM configuration file /etc/pam.d/sshd:

auth required pam_google_authenticator.so

Step 3: User Configuration

For each user that will use keyboard interactive authentication, they need to set up Google Authenticator:

google-authenticator

This command generates a QR code that can be scanned with a mobile authenticator app (e.g., Google Authenticator). The user will receive a verification code whenever they log in.

Step 4: Connecting to the Server

When connecting, the user will provide their password and then be prompted for the MFA code generated by their authenticator app.

Conclusion

Understanding the keyboard interactive authentication method and potential failure points is essential for system administrators. By following the troubleshooting steps outlined above, users can effectively diagnose and resolve issues, ensuring secure and smooth access to SSH servers.

Additional Considerations

Regular Updates: Keep your SSH and PAM modules updated to mitigate security vulnerabilities.
Backup Configurations: Always backup configuration files before making changes.
Logs Review: Regularly review logs for any unauthorized access attempts or anomalies.

By following these guidelines, you can ensure a more secure and reliable SSH environment. If you have further questions or require additional assistance, don’t hesitate to reach out to the community or consult documentation for your specific SSH implementation.

Attribution: Content inspired by community questions and answers on GitHub regarding SSH2 keyboard interactive authentication issues.