hostname/ip does not match certificate's altnames

2025 Vertis

3 min read 12-11-2024

Hostname/IP Does Not Match Certificate's Altnames: A Comprehensive Guide

The dreaded "Hostname/IP does not match certificate's altnames" error is a common headache for website owners and users alike. This error, usually encountered when accessing a website over HTTPS, indicates a mismatch between the domain name you are trying to access and the list of authorized names (also known as Subject Alternative Names or SANs) included in the website's SSL certificate.

This mismatch is a crucial security measure designed to prevent "man-in-the-middle" attacks, where malicious actors intercept communication between a user and a website, potentially stealing sensitive data.

Understanding the Problem

Every website using HTTPS uses an SSL certificate to encrypt communication between the server and your browser. The certificate contains information about the website, including the domain name, the issuing Certificate Authority (CA), and a list of authorized names. This list of authorized names, called Subject Alternative Names (SANs), allows the certificate to cover multiple domain names or IP addresses, preventing the need for separate certificates for each name.

When you visit a website, your browser checks if the hostname in the URL matches the name in the SSL certificate or one of the listed SANs. If a mismatch occurs, the browser raises the "Hostname/IP does not match certificate's altnames" error, signaling a potential security issue.

Causes of the Error

Several factors can cause this error:

Incorrectly configured SSL Certificate: The most common reason is a mismatch between the website's actual hostname or IP address and the names listed in the certificate's SANs.
Misconfigured Server: The server might be configured to listen on the wrong port or IP address.
Typographical Errors: A simple typo in the hostname or certificate configuration can cause the error.
Using an outdated certificate: If the certificate is expired or revoked, it may not be valid for the hostname.
Incorrect domain names in the certificate: The certificate may not include the correct domain name or SANs.
Using a wildcard certificate incorrectly: Wildcard certificates allow for multiple subdomains, but they should only be used when the certificate covers all the subdomains.
Using a self-signed certificate: If you are using a self-signed certificate, the browser may not trust it, leading to the error.

How to Fix the "Hostname/IP does not match certificate's altnames" Error

The solution depends on the root cause. Here's a step-by-step guide to troubleshooting and resolving the error:

1. Verify the Correct Hostname and IP Address:

Confirm your website's hostname: Double-check the website address (URL) you are using.
Find your server's IP address: Use a tool like ping in a command prompt or terminal.

2. Examine the SSL Certificate:

Check the certificate's SANs: Use your browser's built-in security information tool (often accessed by clicking the lock icon in the address bar). Check if the certificate's SANs list the hostname or IP address you are using.
Confirm certificate validity: Check the certificate's expiration date and revocation status.
Consider a wildcard certificate: If you need to cover multiple subdomains, a wildcard certificate might be the best solution.

3. Review Server Configuration:

Check your webserver configuration: The server's virtual host configuration should match the hostname and IP address.
Verify the SSL certificate is correctly installed: Ensure the certificate is installed and configured properly for the appropriate domain name.

4. Contact Your Hosting Provider:

If you're unsure how to configure your server or SSL certificate, contact your hosting provider for assistance.

5. Seek Expert Help:

If you continue to encounter issues or are not comfortable with server configuration, consider hiring an experienced IT professional or web developer to resolve the problem.

Prevention is Key:

Carefully choose and configure your SSL certificate: Select a certificate with the correct SANs for your website.
Regularly check and update your certificates: Ensure that certificates are valid and renewed before they expire.
Use a trusted Certificate Authority (CA): Choose a reputable CA to issue your SSL certificate.

Conclusion

While the "Hostname/IP does not match certificate's altnames" error can be frustrating, understanding the reasons behind it and following the troubleshooting steps outlined above can help you resolve the issue. By ensuring your SSL certificate is properly configured and your server is set up correctly, you can protect your website from security vulnerabilities and provide a safe browsing experience for your users.