NET::ERR_CERT_COMMON_NAME_INVALID - Error Message

Question

I built a website some time ago with Flask. Now all of a sudden when I try to navigate there I get the following:

NET::ERR_CERT_COMMON_NAME_INVALID

Your connection is not private Attackers might be trying to steal your information from www.mysite.org (for example, passwords, messages, or credit cards). Learn more

Does anyone know what's going on?

Answer 1

The error means: The host name you use in the web browser does not match one of the names present in the subjectAlternativeName extension in the certificate.

If your server has multiple DNS entries you need to include all of them into the certificate to be able to use them with https. If you access the server using its IP address like https://10.1.2.3 then the IP address also have to present in the certificate (of course this only makes sense if you have a static IP address that never changes).

Answer 2

The certificate subject alternative name can be a domain name or IP address. If the certificate doesn’t have the correct subjectAlternativeName extension, users get a NET::ERR_CERT_COMMON_NAME_INVALID error letting them know that the connection isn’t private. If the certificate is missing a subjectAlternativeName extension, users see a warning in the Security panel in Chrome DevTools that lets them know the subject alternative name is missing.

https://support.google.com/chrome/a/answer/7391219?hl=en