How to Use the X-permitted-cross-domain-policies Header for Adobe Flash Security

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The X-Permitted-Cross-Domain-Policies header is a crucial security feature for Adobe Flash applications. It helps control how Flash movies interact with data from other domains, reducing the risk of cross-site attacks. Proper configuration of this header ensures your website remains secure while allowing necessary cross-domain data sharing.

Understanding the X-Permitted-Cross-Domain-Policies Header

The X-Permitted-Cross-Domain-Policies header tells the browser and Flash Player what levels of cross-domain access are permitted. It is set on the server and influences how Flash content interacts with other domains. Misconfiguration can either block legitimate data sharing or expose your site to security vulnerabilities.

Common Policy Values

  • none: No cross-domain policies are allowed. Flash cannot access data across domains.
  • master-only: Only the main domain’s policy file is permitted.
  • by-content-type: Policies are allowed based on content type.
  • all: All cross-domain policies are permitted. Use with caution.

Configuring the Header

To set the X-Permitted-Cross-Domain-Policies header, modify your server configuration. For example, in Apache, add the following line to your .htaccess file:

Header set X-Permitted-Cross-Domain-Policies "none"

For Nginx, include this in your server block:

add_header X-Permitted-Cross-Domain-Policies "none";

Best Practices for Security

  • Set the header to none if cross-domain data sharing is not needed.
  • Use master-only for limited access to your main domain’s policy.
  • Regularly review your policies to ensure they meet your security requirements.
  • Test your configuration to verify that Flash content functions correctly without exposing vulnerabilities.

Testing Your Configuration

After configuring the header, test your setup by accessing your site with Flash content. Use browser developer tools or specialized security testing tools to verify that the X-Permitted-Cross-Domain-Policies header is correctly set and that Flash content behaves as expected.

Proper configuration helps protect your site from cross-site scripting and data theft, ensuring a safer environment for users and content.