Cross-Origin-Opener-Policy (COOP)

Cross-Origin-Opener-Policy (COOP) is an important security feature in web development and hosting. Born from the need to mitigate security vulnerabilities associated with cross-origin iframes, COOP arrived to ensure a safer browsing experience for all users.

This policy is used to tell how a document should be treated when embedded in another origin, which helps increase web security by preventing potential attacks. In our article you will learn all you need about COOP, we will show you its impact on web security, the way it works, how to install it on your server, and much more.

What is Cross-Origin-Opener-Policy?

Cross-Origin-Opener-Policy (COOP) is an HTTP header and has become a key security feature for web developers and sysadmins. This protocol tells how web documents should be handled when they are integrated across different origins, thus mitigating potential security threats related to cross-origin iframes.

Mozilla web docs say that “The HTTP Cross-Origin-Opener-Policy (COOP) response header allows you to ensure a top-level document does not share a browsing context group with cross-origin documents.”

COOP’s main objective is to increase web security by establishing guidelines for how browsers interact with content from varied sources. Its main role lies in stopping security threats, which ensures a safer online environment for users.

The role of Cross-Origin-Opener-Policy

COOP’s job is to dictate the treatment of documents from one origin when embedded elsewhere, managing interactions between different origins on a webpage. COOP increases web security by stopping threats like cross-site data leaks and reducing the likelihood of related security vulnerabilities.

By using this header, admins can establish guidelines on how web browsers manage content from different sources to minimize potential exploits.

The Cross-Origin-Opener-Policy header employs a set of directives like “same-origin”, “same-origin-allow-popups”, and “unsafe-none” to define the desired behavior. The “same-origin” directive restricts the embedded document to be treated as same-origin, preventing cross-origin access. “same-origin-allow-popups” extends this to allow popups, enhancing functionality. “unsafe-none” disables COOP, providing flexibility but compromising security.

BuiltWith reports that this feature is used by only 4000 of the top 1 million websites out there.

Cross-Origin-Opener-Policy and COEP

Cross-Origin-Opener-Policy (COOP) and Cross-Origin-Embedder-Policy (COEP) are related security headers, often employed together to increase overall security in websites.

COOP rules the treatment of documents from one origin when embedded somewhere else, managing interactions between diverse origins within a webpage, and COEP focuses on controlling the embedding context of a resource. It tells how a resource should be embedded and specifies who is authorized to perform the embedding.

Combining both headers allows devs and admins to establish great security measures, addressing various aspects of cross-origin security.

Is Cross-Origin-Opener-Policy the same as CORS?

No, Cross-Origin-Opener-Policy (COOP) and Cross-Origin Resource Sharing (CORS) are different security rules, though each addresses different aspects of cross-origin interactions, so they are related and often used together.

COOP determines how documents from one origin are treated when embedded in another site, focusing on security measures for cross-origin iframes. Meanwhile, CORS is a more robust mechanism that deals with cross-origin HTTP requests, managing the permissions for resources requested from a different domain.

While both contribute to handling cross-origin scenarios, COOP primarily deals with document treatment, while CORS is concerned with controlling access to resources during HTTP requests.

Cross-Origin-Opener-Policy as a vulnerability

Cross-Origin-Opener-Policy (COOP) is not a vulnerability itself. It serves as a security measure to address potential vulnerabilities related to cross-origin iframes.

The effectiveness of COOP depends on an accurate implementation and configuration, so if misconfigured or used improperly, it could result in unintended consequences or affect the functionality of websites.

It’s important for sysadmins to have a clear understanding of COOP and apply its policies carefully to avoid security risks. COOP is a tool designed to mitigate vulnerabilities related to cross-origin iframe interactions, and its proper implementation is crucial for maintaining a secure web environment.

Cross-Origin-Opener-Policy browser compatibility

Cross-Origin-Opener-Policy (COOP) was launched in May 2020, and major web browsers have supported it since then, including Google Chrome and Microsoft Edge. Support on Mozilla Firefox came 2 months later in July 2020. Apple Safari also started to support it in December 2021. Other web browsers like Opera and Internet Explorer have no support for it.

Cross-Origin-Opener-Policy examples

Let’s see a few common examples of how Cross-Origin-Opener-Policy (COOP) works. Remember that this is an HTTP header, and it can be set with different directives.

Same-Origin Policy:

Cross-Origin-Opener-Policy: same-origin

This directive ensures that the embedded document is treated as same-origin, restricting cross-origin access.

Same-Origin with Allow-Popups:

Cross-Origin-Opener-Policy: same-origin-allow-popups

Extends the “same-origin” policy to allow popups, enhancing functionality while maintaining a same-origin treatment.

Unsafe-None (No COOP):

Cross-Origin-Opener-Policy: unsafe-none

Disables COOP entirely, providing flexibility but compromising security. Not recommended for most scenarios.

Cross-Origin-Opener-Policy best practices

Here we will guide you through some of the best practices and considerations related to COOP.

• Precise directive selection: choose COOP directives like “same-origin”, “same-origin-allow-popups”, or “unsafe-none” with precision based on your security requirements. Understanding each directive’s implications is crucial for effective risk mitigation.
• Compatibility testing: verify COOP compatibility across different browsers to guarantee consistent security measures. Regularly test your website to detect any issues in how COOP directives are interpreted by various browsers.
• Combine it with COEP: use both Cross-Origin-Opener-Policy (COOP) and Cross-Origin-Embedder-Policy (COEP) for great security coverage. Integrating both headers allows you to deal with various aspects of cross-origin security effectively.
• Dynamic policy adjustment: try to implement mechanisms for dynamic adjustment of COOP policies based on your security needs. Adaptable policies enable you to respond faster to new threats and maintain a strong defense against potential risks.

Challenges of Cross-Origin-Opener-Policy implementation

Implementing Cross-Origin-Opener-Policy (COOP) can enhance web security, but it’s not without its challenges. Below are some common issues that developers and sysadmins may encounter during COOP implementation.

• Browser support discrepancies: different web browsers may interpret COOP directives differently or have varying levels of support. Ensure thorough testing across multiple browsers to identify any compatibility issues and change configurations accordingly.
• Incorrect directive selection: choosing the wrong COOP directive or misconfiguring headers can weaken security or disrupt functionality. Take your time to understand each directive and select the appropriate one based on your specific security requirements.
• Restrictive policies: implementing overly restrictive COOP policies may inadvertently block legitimate cross-origin interactions, leading to functionality issues or user experience degradation. Aim to strike a balance between security and functionality when defining COOP directives.
• Latency impact: COOP may introduce additional latency, particularly when cross-origin resources are involved. Monitor performance metrics and optimize configurations to minimize any performance issues.
• Data protection regulations: ensure that your COOP settings align with relevant data protection regulations, such as GDPR or HIPAA, to safeguard user privacy and maintain compliance. Review privacy impact and perform audits often to verify complaint with regulatory requirements.

How to configure Cross-Origin-Opener-Policy

Enabling COOP is pretty straightforward, so let’s check how to do it in popular web servers like Apache and Nginx.

Enabling Cross-Origin-Opener-Policy in Apache

To enable Cross-Origin-Opener-Policy (COOP) in Apache, start by modifying your Apache configuration file (httpd.conf or a virtual host file). Use the Header directive to set the desired COOP header based on your requirements. For example:

Header set Cross-Origin-Opener-Policy "same-origin"

This example configures COOP to “same-origin”, restricting the handling of embedded documents to the same origin.
Now save the configuration file and restart your Apache server for the changes to take effect:

systemctl restart apache2

Setting up Cross-Origin-Opener-Policy in Nginx

To activate Cross-Origin-Opener-Policy (COOP) in Nginx, first open your Nginx configuration file, usually /etc/nginx/nginx.conf or located within /etc/nginx/conf.d/.

Find the server block corresponding to your domain and include the following line to define the COOP header:

add_header Cross-Origin-Opener-Policy "same-origin";

In this example, the COOP header is set to “same-origin”, limiting the handling of embedded documents to the same origin.
Save your configuration file and test your Nginx config:

nginx -t

If the test passes, reload Nginx to apply the changes:

systemctl reload nginx

Or restart it:

systemctl restart nginx

How to set Cross-Origin-Opener-Policy on IIS

Like most headers, setting up COOP on IIS is pretty easy.

1. Start by opening the IIS Manager and choosing the site where you want to set the header.
2. Access HTTP Response Headers and click on Add.
3. Enter the following:
   • Name: Cross-Origin-Opener-Policy
   • Value: same-origin (or another appropriate value).
4. Save the changes.

Cross-Origin-Opener-Policy FAQ

Let’s answer some of the most common questions related to COOP.

Is Cross-Origin-Opener-Policy obsolete?

No, Cross-Origin-Opener-Policy (COOP) is not obsolete, it remains an important security feature. COOP is used to address security risks linked to cross-origin iframes by telling how documents from one origin should be managed when incorporated into another, thus enhancing web security.

Why is Cross-Origin-Opener-Policy important for web security?

Cross-Origin-Opener-Policy has a key role in web security as it dictates the treatment of documents from one origin when integrated into a different site. Thanks to the precise guidelines that are established by the COOP headers, admins can stop potential security risks, including cross-site data leaks and vulnerabilities related to cross-origin iframes. Due to its authority over cross-origin interactions, Cross-Origin-Opener-Policy contributes to establishing a safer web experience for all users.

How to check if COOP is enabled on my website

Now let’s see how to test your current Cross-Origin-Opener-Policy settings, please follow this guide:

1. Access our web misconfiguration scanner.
2. Type your domain in the scan box.
3. Check the two boxes below, which are called ‘Clear cache’ and ‘Follow redirects’.
4. Click the Scan button.
5. Now scroll down and look for the section named ‘HTTP Security Headers’, and check your ‘Cross-Origin-Opener-Policy’ test results: a ‘Passed’ in green is good, but if you get a ‘Failed’ in red it means that you need to update your current settings.

Summary

Cross-Origin-Opener-Policy (COOP) is a key security feature that responds to the need to mitigate security vulnerabilities linked with cross-origin iframes. This HTTP header has the task of determining how documents should be treated when embedded in another origin, thus contributing to enhancing web security, and providing a safer browsing experience for users.

COOP establishes guidelines for how browsers should interact with content from different sources, preventing potential security issues such as cross-site data leaks and reducing the likelihood of related vulnerabilities. In conjunction with Cross-Origin-Embedder-Policy (COEP), COOP forms a robust duo of security headers, often employed together to fortify overall website security.