Solving the Infuriating Caddy Subdomain Issue: `ERR_SSL_VERSION_OR_CIPHER_MISMATCH`

Ah, the sweet taste of frustration when your Caddy setup refuses to play nice with subdomains. You’ve spent hours crafting the perfect server configuration, only to be met with the dreaded `ERR_SSL_VERSION_OR_CIPHER_MISMATCH` error. Worry not, dear reader, for we’re about to embark on a journey to conquer this pesky issue once and for all!

Understanding the Problem

Before we dive into the solution, let’s take a step back to understand what’s causing this error. The `ERR_SSL_VERSION_OR_CIPHER_MISMATCH` error occurs when there’s a mismatch between the SSL/TLS version or cipher suite used by the client (usually a web browser) and the server. This can happen when:

• The client is using an outdated version of TLS (e.g., TLS 1.0) that’s no longer supported by the server.
• The client and server are using different cipher suites, making it impossible to establish a secure connection.
• The subdomain configuration is not properly set up, causing the server to serve the wrong SSL certificate or configuration.

Caddy Configuration: A Deeper Dive

To better understand the solution, let’s examine a typical Caddy configuration file:

{
    {
        tls {
            certificates {
                "${HOME}/certs/fullchain.pem"
                "${HOME}/certs/privkey.pem"
            }
        }
        subdomains {
            sub1.example.com
            sub2.example.com
        }
    }
}

In this example, we have a single site block with TLS enabled and a subdomains section listing two subdomains: sub1.example.com and sub2.example.com. Now, let’s explore how to troubleshoot and resolve the `ERR_SSL_VERSION_OR_CIPHER_MISMATCH` error.

Step 1: Verify SSL Certificate and Private Key

Ensure that your SSL certificate and private key are correctly configured and in the right location. Check that the certificate chain is complete and the private key is not encrypted. You can do this using the following commands:

openssl x509 -in fullchain.pem -text -noout
openssl rsa -in privkey.pem -check

If you find any issues with your certificate or private key, obtain a new pair from your certificate authority or regenerate them using a tool like OpenSSL.

Step 2: Check Caddy Configuration

Review your Caddy configuration file for any discrepancies or typos. Make sure the subdomains section is correctly formatted and the TLS block is properly configured. A single misplaced bracket or comma can cause the error.

Try running Caddy with the `–debug` flag to see if it outputs any errors or warnings:

caddy run --debug

Step 3: Update Caddy to Support Modern TLS Versions

Caddy, by default, supports TLS 1.2 and 1.3. However, if you’re using an older version of Caddy, it might only support TLS 1.0 or 1.1. Update Caddy to the latest version to ensure it supports modern TLS versions:

caddy upgrade

Alternatively, you can specify the supported TLS versions in your Caddy configuration:

tls {
    ...
    tls_versions tls1.2 tls1.3
}

Step 4: Configure Cipher Suites

To avoid cipher suite mismatches, specify a list of supported cipher suites in your Caddy configuration. You can use a tool like OpenSSL to generate a list of recommended cipher suites:

openssl ciphers -v 'TLSv1.2:+AESGCM:HIGH:!aNULL:!eNULL'

Add the recommended cipher suites to your Caddy configuration:

tls {
    ...
    ciphers TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
           TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
           TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
           TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
}

Step 5: Verify Subdomain Configuration

Double-check that your subdomain configuration is correct and the subdomains are properly routed to the correct SSL certificate. You can use a tool like `dig` or `nslookup` to verify the DNS resolution:

dig +short sub1.example.com
dig +short sub2.example.com

Make sure the subdomains point to the correct IP address and the SSL certificate is correctly served.

Step 6: Test and Validate

Restart Caddy and test your subdomains using a tool like `curl` or a web browser:

curl -v -k https://sub1.example.com
curl -v -k https://sub2.example.com

If you still encounter the `ERR_SSL_VERSION_OR_CIPHER_MISMATCH` error, try debugging the issue using Caddy’s built-in debugging tools or consult the Caddy documentation for further guidance.

Additional Tips and Tricks

To avoid future issues, keep the following tips in mind:

• Regularly update Caddy and your SSL certificates to ensure you have the latest security patches and features.
• Use a robust SSL certificate management system, like Let’s Encrypt or a commercial certificate authority, to automate certificate renewal and revocation.
• Monitor your server’s SSL/TLS configuration using tools like SSL Labs or Why No HTTPS to identify potential issues before they become major problems.

Conclusion

Congratulations! You’ve successfully navigated the treacherous waters of the `ERR_SSL_VERSION_OR_CIPHER_MISMATCH` error. By following these steps, you should now have a Caddy setup that correctly serves subdomains with the latest TLS versions and cipher suites. Remember to stay vigilant and keep your Caddy configuration up-to-date to ensure the best possible security for your users.

Common Errors	Solutions
ERR_SSL_VERSION_OR_CIPHER_MISMATCH	Verify SSL certificate, private key, and Caddy configuration. Update Caddy and specify supported TLS versions and cipher suites.
cipher suite mismatch	Specify supported cipher suites in Caddy configuration.
TLS version mismatch	Update Caddy to support modern TLS versions (TLS 1.2 and 1.3).

Now, go forth and conquer the world of Caddy subdomains with confidence!

Frequently Asked Question

Are you struggling with the pesky “ERR_SSL_VERSION_OR_CIPHER_MISMATCH” error on your Caddy subdomain? Don’t worry, we’ve got you covered! Check out these frequently asked questions to get your site up and running in no time.