ERR_SSL_UNRECOGNIZED_NAME_ALERT: What It Means

• nginx has no server_name for the requested domain
• Apache is missing a <VirtualHost> with ServerName
• The DNS A record points to an IP where the domain is not configured
• The CDN/reverse proxy does not know the backend domain
• Cloudflare "Full (strict)" without an origin certificate

1. Add server_name example.com www.example.com; to nginx and reload
2. In Apache: <VirtualHost *:443> ServerName example.com ...</VirtualHost>
3. Check DNS — the A record must point to your web server's IP
4. CDN: set the exact Host header in the origin section
5. Cloudflare: install an origin certificate (free in the dashboard)

Check SSL Certificate →

server {
    listen 443 ssl http2;
    server_name example.com;

    ssl_certificate     /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    ssl_protocols       TLSv1.2 TLSv1.3;
    ssl_ciphers         ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
    ssl_prefer_server_ciphers off;

    ssl_stapling        on;
    ssl_stapling_verify on;
}

• NET::ERR_CERT_AUTHORITY_INVALID
• ERR_CERT_DATE_INVALID
• ERR_SSL_PROTOCOL_ERROR
• SSL Handshake Failed
• All SSL errors

The ERR_SSL_UNRECOGNIZED_NAME_ALERT error in Chrome indicates a Server Name Indication (SNI) mismatch, where the requested hostname does not match the SSL certificate's domain. To resolve this, ensure that the correct SSL certificate is installed for the domain, and verify the server configuration to allow SNI. Use commands like openssl s_client -connect yourdomain.com:443 -servername yourdomain.com to diagnose the issue.

The ERR_SSL_UNRECOGNIZED_NAME_ALERT error occurs when the hostname specified in the SNI does not match the SSL certificate presented by the server. This mismatch can happen for several reasons, including misconfigured server settings, expired certificates, or incorrect DNS entries. When a client, such as Chrome, initiates a secure connection, it sends the hostname through SNI to the server, expecting it to return the appropriate SSL certificate. If the server fails to recognize the name, Chrome will block the connection, raising the error.

To further understand this error, consider the following components:

• Server Name Indication (SNI): An extension of the TLS protocol that allows clients to specify the hostname they are trying to connect to. It is essential for hosting multiple SSL certificates on a single IP address.
• SSL Certificate: A digital certificate that authenticates the identity of a website and encrypts data in transit. The certificate must match the domain being accessed.
• Common Causes: Incorrect certificate installation, expired certificates, or misconfigured web servers.

To check for SNI issues, use the command:

openssl s_client -connect yourdomain.com:443 -servername yourdomain.com

This command connects to the specified domain and outputs the SSL certificate details. Look for the subject and issuer fields to ensure they align with the requested hostname.

To resolve the ERR_SSL_UNRECOGNIZED_NAME_ALERT error, follow these steps:

1. Validate SSL Certificate: Use tools like SSL Checker to verify that the SSL certificate is correctly issued for your domain.
2. Check Server Configuration: Ensure your web server is configured to support SNI. This typically involves settings in the server configuration files.
3. Update DNS Records: Ensure that the DNS records point to the correct server that has the intended SSL certificate.
4. Reinstall or Renew SSL Certificate: If the SSL certificate is expired or incorrectly installed, follow the vendor's instructions to reinstall or renew it.

For example, if you are using Apache, your configuration might look like this:

<VirtualHost *:443>
    ServerName yourdomain.com
    SSLEngine on
    SSLCertificateFile /path/to/certificate.crt
    SSLCertificateKeyFile /path/to/private.key
    SSLCertificateChainFile /path/to/chainfile.pem
</VirtualHost>

Ensure that the ServerName directive matches the hostname the client is requesting. After making any changes, restart the server using:

sudo systemctl restart apache2

or for Nginx:

sudo systemctl restart nginx

Finally, clear your browser cache and try accessing the site again to see if the error persists. If issues continue, consider checking firewall settings or consulting with your hosting provider for further assistance.