Cert_common_name_invalid

MIster jashon

7 min read

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Oct 11, 2024

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What is the 'cert_common_name_invalid' Error?

The "cert_common_name_invalid" error is a common issue encountered when working with SSL/TLS certificates and applications that utilize them. This error indicates a mismatch between the Common Name (CN) specified in the SSL certificate and the hostname or domain name used in the application's request. Let's delve into understanding this error and its possible solutions.

Understanding the SSL Certificate Common Name (CN)

An SSL certificate is a digital document that binds a public key to an identity (a website, server, or other entity). A crucial component of an SSL certificate is the Common Name (CN). This field, usually in the form of a domain name, plays a vital role in secure communication.

How does the CN work?

When a web browser or other application attempts to establish a secure connection to a website, it first verifies the SSL certificate. This verification process involves comparing the CN specified in the certificate against the hostname or domain name requested in the connection.

The Problem:

When there's a mismatch between the CN and the actual hostname or domain name, the browser or application sees this as an inconsistency and triggers the "cert_common_name_invalid" error.

Example:

Imagine you're visiting a website with the address "www.example.com". If the SSL certificate's CN is "example.com", the browser will flag an error because "www.example.com" and "example.com" are different.

Why does this error occur?

Several scenarios can lead to this error:

1. Misconfigured SSL certificate: This is the most common cause. During the SSL certificate generation process, the CN might have been entered incorrectly or accidentally.
2. Incorrect hostname in application: The application might be configured to use a different hostname than the one in the SSL certificate's CN.
3. Wildcard certificate mismatch: If a wildcard certificate (e.g., *.example.com) is used, and the application attempts to connect using a subdomain that's not covered by the wildcard, the error can occur.

Troubleshooting and Solutions:

1. Verify the SSL certificate:

   • Ensure the CN in the SSL certificate matches the hostname or domain name you're using.
   • Check the validity and expiration date of the certificate.
   • Tools to help:
     • You can use online certificate checkers like SSL Labs (https://www.ssllabs.com/ssltest/) to analyze your certificate and identify any issues.

2. Check the application configuration:

   • Verify the hostname or domain name configured in your application code or settings matches the CN in the certificate.
   • Check for any typos or inconsistencies in the hostname entries.

3. Review DNS records:

   • Make sure your DNS records correctly point to the server hosting your website.
   • Use tools like dig or nslookup to check the A and CNAME records associated with your domain.

4. Use a correct certificate type:

   • Wildcard certificates are suitable for multiple subdomains. Ensure the wildcard pattern covers the domain you're connecting to.
   • SAN (Subject Alternative Name) certificates allow you to list multiple domain names and hostnames within a single certificate.

5. Regenerate the certificate (if necessary):

   • If you've confirmed that the CN in the certificate is incorrect, you'll need to regenerate the certificate with the correct hostname or domain name.

Commonly Used Tools:

• OpenSSL: A powerful command-line tool for managing SSL certificates.
• Let's Encrypt: A popular free Certificate Authority that provides SSL certificates.
• Certbot: An automated tool to obtain and install SSL certificates.
• SSL Labs: A website for analyzing and testing SSL certificates.

Example (using OpenSSL):

To check the CN of an SSL certificate using OpenSSL, you can use the following command:

openssl s_client -showcerts -connect example.com:443