HSTS Missing From HTTPS Server Error Guide

Jun 23 2024 by Oskay Günaçar

What Is HSTS Missing from HTTPS Server

The "HSTS Missing from HTTPS Server" error is a security issue where a server that uses HTTPS (Hyper Text Transfer Protocol Secure) does not have HSTS (HTTP Strict Transport Security) enabled.

HSTS is a security feature that helps protect websites against certain types of attacks such as protocol downgrade attacks and cookie hijacking.

Here's what the error means:

  1. HSTS Policy: When a server implements HSTS, it sends a header in its responses that instructs the browser to only connect to the server using a secure HTTPS connection for a specified period. This helps ensure that users can only access the site securely.

  2. Error Implication: If this error is detected (for example, by a security scanner or browser), it means that while the server is using HTTPS, it has not set the HSTS policy in its HTTP headers. This could potentially leave the server and its users vulnerable to certain types of attacks.

  3. Security Risk: Without HSTS, even if a site uses HTTPS, it's possible for an attacker to intercept the initial request to the server if it's made over HTTP (for example, if a user types example.com instead of https://example.com). The attacker can then redirect the user to a malicious site or perform a man-in-the-middle attack.

Why Does the “HSTS Missing from HTTPS Server” Error Occur?

The "HSTS Missing" error occurs because a web server has not been configured to send the HTTP Strict Transport Security (HSTS) header in its responses. Here's a breakdown of why this situation might arise:

1. Lack of Awareness or Knowledge

Many website administrators might not be aware of HSTS or its importance in enhancing web security. This lack of knowledge can lead to its non-implementation during the setup or maintenance of HTTPS servers.

2. Incomplete or Incorrect Configuration

Even when administrators are aware of HSTS, errors in server configuration might prevent the proper sending of the HSTS header. For instance, the header might be set incorrectly, only sent under certain conditions, or omitted entirely.

3. Legacy Systems

Older systems or legacy platforms might not support the automatic addition of HSTS headers, requiring manual configuration. In some cases, these systems may be neglected or the cost and effort of updating them may be deemed too high, resulting in a failure to implement HSTS.

4. Misunderstanding of HTTPS

Some administrators might believe that simply using HTTPS is enough for security, not realizing the additional protection layer that HSTS provides against certain types of cyber attacks, like protocol downgrade attacks and cookie hijacking.

5. Initial Testing and Deployment Oversights

During the initial setup and testing phases of a website, HSTS might be overlooked or deliberately left out to simplify troubleshooting of HTTPS issues. However, it might not be added later on when moving to a production environment.

6. Fear of Commitment

Implementing HSTS can be seen as a significant commitment because, once enabled, it forces all users to connect via HTTPS for a specified time period (defined by the max-age parameter). This can deter some administrators if they are unsure about their server’s ability to handle HTTPS exclusively, especially considering issues related to certificate renewal and management.

7. Preload List Requirements

For websites opting into the HSTS preload list, which is a list that browsers use to know in advance that a site should only be accessed using HTTPS, there are stringent requirements that need to be met. Some administrators might delay HSTS implementation while ensuring compliance with all preload requirements.

Addressing the "HSTS Missing" error involves educating administrators about HSTS, ensuring proper and complete server configuration, and maintaining an ongoing security protocol review to ensure that HSTS and other security measures are appropriately managed.

Why Is HSTS Missing From HTTPS Server Error Important?

The "HSTS Missing from HTTPS Server" error is important for several reasons, primarily revolving around the security implications of not enforcing a strict HTTPS-only policy across a website. Here’s why this error matters:

Increased Vulnerability to Attacks

Without HSTS, a website is more susceptible to certain types of cyber attacks, such as man-in-the-middle (MitM) attacks. Attackers can exploit the lack of HSTS to intercept or alter data transmitted between the user and the server, potentially stealing sensitive information like login credentials or personal data.

Protocol Downgrade Attacks

Without HSTS, attackers can force connections to revert from HTTPS to HTTP, which does not encrypt data. This makes it easy for attackers to read or modify any data passed back and forth between the user and the web server.

Cookie Hijacking

If a website doesn't secure its cookies (particularly session cookies) with the Secure flag, these can be transmitted over HTTP. In the absence of HSTS, an attacker can manipulate the communication to use HTTP and thus intercept these cookies.

Loss of User Trust and Credibility

Modern browsers may flag websites that do not implement HSTS as less secure, warning users when they attempt to access them. This can deter users from visiting the website, impacting its credibility and reducing traffic and transactions.

Compliance Issues

Depending on the nature of the business and the data it handles, not implementing HSTS could lead to non-compliance with regulatory requirements, particularly those concerning data protection and privacy (like GDPR). This can result in penalties and legal issues.

SEO Impact

Search engines tend to favor secure websites. Lack of HSTS might affect a website’s SEO ranking negatively because it’s seen as less secure.

Implementing HSTS is a relatively straightforward way to enhance the security of a website. It ensures that all communications between the browser and the server are conducted over HTTPS, providing a more secure and reliable user experience.

What Are The Dangers Of The HSTS Missing From Https Server Error?

Exposure to Man-in-the-Middle Attacks

Without HSTS, a site is more vulnerable to man-in-the-middle attacks where an attacker intercepts the communication between a user's browser and the web server. This can result in sensitive data being stolen, such as personal information, login credentials, and payment details.

Risk of Protocol Downgrade Attacks

HSTS prevents attackers from forcing connections to downgrade from secure HTTPS to less secure HTTP. Without HSTS, attackers can potentially induce browsers to use HTTP, enabling them to intercept and tamper with data transmitted between the user and the server.

Cookie Theft

Cookies that are not flagged as secure can be transmitted over HTTP. If HSTS is not enforced, attackers can execute attacks that strip the secure layer (HTTPS), intercepting these cookies. This can lead to session hijacking, where an attacker gains unauthorized access to the user's session.

Decreased User Confidence

Modern web browsers sometimes display security warnings or indicators for sites that do not use HTTPS exclusively or correctly implement security features like HSTS. Users may see these warnings and choose not to trust or engage with the site, potentially leading to a loss of traffic or revenue.

Compliance and Legal Risks

For businesses subject to data protection regulations (like GDPR), failing to implement HSTS could be seen as not having adequate technical measures in place to ensure the security of data in transit. This could lead to legal penalties and damage to the company's reputation.

Search Engine Optimization (SEO) Impact

Search engines prioritize security as a ranking factor. Websites that do not implement necessary security measures like HSTS may experience a negative impact on their SEO, making it harder for potential visitors to find the site through search engines.

Overall, the absence of HSTS can significantly weaken the security posture of a website, making it prone to various types of cyber threats and attacks that can compromise user data and trust.

How to Detect Missing HSTS Error from a Website?

Detecting a missing HTTP Strict Transport Security (HSTS) configuration on a website involves checking whether the server sends the proper Strict-Transport-Security header in its HTTPS responses. Here are some effective methods to check for HSTS:

1. Browser Developer Tools

You can use the developer tools available in most modern web browsers to inspect the HTTP headers sent by the server:

  • Open the website in your browser.
  • Right-click on the page and select Inspect or press Ctrl+Shift+I (Windows/Linux) or Cmd+Option+I (Mac).
  • Go to the Network tab and reload the page.
  • Click on the first entry, usually the request for the page itself.
  • Look for the Headers section and check if there is a Strict-Transport-Security header present.

If this header is missing from the response, then the website does not implement HSTS.

2. Command Line Tools (cURL)

Using command-line tools like cURL can help you quickly check headers:

curl -I https://example.com

Replace https://example.com with the URL of the site you want to check. Look for the Strict-Transport-Security line in the output. If it's not present, HSTS is not implemented.

3. Online Tools

Several online services can analyze a website’s headers and report on their security settings, including whether HSTS is configured. Tools like SSL Labs' SSL Test or securityheaders.com can provide detailed reports.

4. Automated Scanning Tools

For larger sites or those managing multiple domains, automated scanning tools can be integrated into your security practices. These tools can regularly scan and report on the security headers, including HSTS, across all your web properties.

5. Browser Extensions

Browser extensions like HTTP Header Live (Firefox) can display all HTTP headers in real time as you browse. Such tools can be useful for quickly checking the headers without needing to open developer tools every time.

By using these methods, you can effectively detect whether HSTS is missing from a website's configuration and take necessary steps to implement it if required. This is a critical step in ensuring that all data transmitted between the user and the website is secured against common web-based attacks.

How to Fix the HSTS Missing From HTTP Server Error?

To fix the "HSTS Missing from HTTPS Server" error, you need to configure your web server to send the Strict-Transport-Security header in its HTTPS responses. Here are steps for implementing HSTS on some of the most common web servers:

Apache HTTP Server

  1. Edit the Configuration File: Open your Apache configuration file (httpd.conf or ssl.conf usually found in /etc/httpd/ or /etc/apache2/).
  2. Add HSTS Header: Insert the following line inside the <VirtualHost> block for your SSL configuration:
    Header always set Strict-Transport-Security "max-age=63072000; includeSubDomains; preload"
  3. Restart Apache: Save the configuration file and restart Apache to apply the changes:
    sudo systemctl restart apache2


  1. Edit the Configuration File: Open your Nginx configuration file (usually found in /etc/nginx/nginx.conf or within the /etc/nginx/sites-available/ directory).
  2. Add HSTS Header: Add the following line inside the server block listening on port 443:
    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
  3. Restart Nginx: Save the file and restart Nginx to enforce the changes:
    sudo systemctl restart nginx

Microsoft IIS

  1. Open IIS Manager: Launch the Internet Information Services (IIS) Manager.
  2. Select Your Website: Click on your website listed in the Connections panel.
  3. Open HTTP Response Headers: Double-click on "HTTP Response Headers" in the middle panel.
  4. Add Custom Header: Click on "Add" in the Actions panel, and set:
    • Name: Strict-Transport-Security
    • Value: max-age=63072000; includeSubDomains; preload
  5. Apply Changes: Click OK and close the IIS Manager.


If you're using Cloudflare, you can enable HSTS via their dashboard:

  1. Log in to Cloudflare: Go to the Cloudflare dashboard and select your site.
  2. Navigate to SSL/TLS: Click on the SSL/TLS tab.
  3. Enable HSTS: Scroll down to HTTP Strict Transport Security (HSTS) and set up your policy.

General Recommendations

  • Set a Long max-age: The max-age directive tells browsers how long to remember that the site should only be accessed using HTTPS. A common recommendation is 63072000 seconds (2 years).
  • Include Subdomains: The includeSubDomains directive ensures that HSTS is applied to all subdomains as well.
  • Consider Preloading: Adding preload to the header and submitting your site to the HSTS preload list (https://hstspreload.org/) makes browsers aware of your HSTS policy before their first visit. Note: This step is irreversible and should be done with caution.

After configuring HSTS, it's important to test your website to ensure the header is properly set and no mixed content issues arise. This will help maintain site functionality and user experience while enhancing security.


Implementing HTTP Strict Transport Security (HSTS) is a critical step for enhancing the security of any website that uses HTTPS. As we've explored, the absence of HSTS can leave a site and its users vulnerable to a range of security threats, including man-in-the-middle attacks, protocol downgrade attacks, and cookie hijacking. These vulnerabilities not only compromise user data but can also erode trust in a website, affect compliance with security regulations, and negatively impact search engine rankings.

Addressing the "HSTS Missing" error is more than a technical necessity; it is a commitment to user safety and data integrity. By configuring your web server to include the HSTS header—and ensuring that it's correctly implemented—you safeguard all communications against interception and tampering. Moreover, adopting HSTS demonstrates a proactive stance on security, enhancing your credibility and trustworthiness in the eyes of your users and partners.

As we have seen, detecting and fixing the absence of HSTS is straightforward. Whether you are using Apache, Nginx, IIS, or a cloud-based platform like Cloudflare, the steps to enable HSTS are simple and can be implemented quickly. Additionally, the adoption of automated tools for continuous monitoring can ensure that your HSTS policy remains effective and that your site continues to meet evolving security standards.

In conclusion, the implementation of HSTS should be considered a best practice for all websites that use HTTPS. It is a small but powerful addition to your security arsenal, one that significantly strengthens your site's defenses against common and potentially devastating attacks. Remember, in the realm of cybersecurity, proactive measures are always better than reactive ones. By implementing HSTS, you are taking a significant step forward in securing your digital environment and protecting your users' data.

Oskay Günaçar
Oskay Günaçar is a Technical SEO expert and backend developer. His main areas of interest are back-end programming, Python, Django, Go, semantic SEO, technical SEO. With more than 5 years of SEO experience, he has held SEO specialist positions at İkiler, Webtures, Boosmart, and Storyly.io companies, and has been involved in numerous projects as an outsourced expert. Through the TechSEOHub website, he aims to share the expertise and experience he has gained from managing and developing (SEO) processes for many successful and large websites in the industry, and to produce content for easy access to accurate and high-quality information.