Learn how to resolve the “Server sent invalid HSTS policy “error“. Our Server Management Support team is here to help you with your questions and concerns.

Server sent invalid HSTS policy error – Resolved

If you have been running into the following error recently, you are in the right place:

Server sent invalid HSTS policy

According to our experts, this error occurs when a web server sends an invalid HTTP Strict Transport Security policy to the client’s browser.

HSTS, short for HTTP Strict Transport Security policy, is a security feature that tells the browser to access a website over a secure HTTPS connection. This prevents potential attacks.

After a server sends an invalid HSTS policy, it means that the policy is not correctly formatted or contains incorrect directives. This can result in the browser displaying an error message to the user.

Server sent invalid HSTS policy error- Causes & Fixes 

Let’s take a look at some of the causes and fixes for this error:

• If the HTTP response header is missing or not properly formatted, the browser may consider it invalid. In this case, we have to ensure the server sends the HSTS header correctly. The HSTS header usually looks like this:

  Strict-Transport-Security: max-age=31536000; includeSubDomains

  Here, max-age directive is the in seconds that the browser should remember to access the website over HTTPS.
• Next, we have to verify the server configuration is set up correctly. Our experts recommend checking that the directives and values in the configuration file or server settings are accurate. Additionally, look for typos and formatting errors in the HSTS policy.
• In case the website has a combination of HTTP and HTTPS resources it can result in an error. This is why we have to ensure that all resources are served over HTTPS. We can also check the website source code and update any HTTP URLs to use HTTPS.
• Furthermore, if the server’s HSTS policy was previously misconfigured or has changed, the browser may still have the old policy cached. Then, clearing the browser cache can help.

  Additionally, we can use the preload directive in the HSTS header to submit our website to the HSTS preload list.

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Conclusion

In brief, our Support Techs demonstrated how to resolve the “Server sent invalid HSTS policy error.