Learn how to fix the 0x800b0109 IIS Client Certificate error. Our IIS Support team is here to help you with your questions and concerns.

0x800b0109 IIS Client Certificate | Fixed

Some of our customers have been having trouble with the “0x800b0109” error code recently.

Fortunately, our experts were able to get them back on track in no time.

This error is related to IIS and client certificates. It lets us know there is a problem with the validation of the client certificate presented during the SSL/TLS handshake.

IIS is a web server developed by Microsoft. It is used to host websites and web applications on Windows-based systems. Client certificates are used in SSL/TLS mutual authentication.

In other words, it is used when both the server and the client present certificates to each other to establish a secure connection.

In fact, when a client tries to access an IIS-hosted website that needs a client certificate, IIS validates the client certificate to make sure it is trusted and valid.

Furthermore, the “0x800b0109” error code comes with the following error message:

A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider

As the error message indicates, the certificate chain could not be validated, and the root certificate authority is not trusted by the server.

Troubleshooting Tips

Let’s take a look at some of the common reasons and fixes for the “0x800b0109” error:

• One of the most common causes behind this error is that the root certificate authority that issued the client certificate is not present in the server’s trusted root certificate store.

  We have to make sure that the root CA certificate is installed in the Trusted Root Certification Authorities store on the server.
• In some cases, the client certificate is issued by an intermediate. However, the server may not have the intermediate certificate installed. In this case, we have to install intermediate certificates along with the root CA certificate in the server’s certificate store.
• If the client certificate is no longer valid, the validation will fail. Hence, we have to verify that the client certificate is still valid.
• Next, make sure the client certificate is bound to the correct website in IIS.
• The certificate chain order is important during the validation process. We have to make sure that the client certificate and intermediate certificates are in the correct order during the SSL/TLS handshake.
• Then, check if the client certificate has expired. If it has, the validation will fail.
• Next, make sure that the client certificate is correctly encoded and in the right format for the server to validate it.
• In case the client is going through a proxy server, the proxy server’s certificate configuration may interfere with the client certificate validation. So, we have to review the proxy server’s certificate settings.

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Conclusion

In summary, our Support Techs demonstrated how to fix the 0x800b0109 error code in IIS.