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CSP Allow-list Experiment

sourceSimon Willison
calendar_todayMay 13, 2026
schedule1 min read
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EXECUTIVE SUMMARY

Innovative CSP Allow-list Experiment Enhances Web Security Protocols

Summary

The article discusses a CSP Allow-list Experiment that demonstrates how to load an application within a Content Security Policy (CSP) protected sandboxed iframe. It highlights a custom fetch() function that intercepts CSP errors and prompts users to add domains to an allow-list.

Key Points

  • The experiment showcases the use of a sandboxed iframe to enhance security through CSP.
  • A custom fetch() function is utilized to intercept CSP errors.
  • Users are prompted to add domains to an allow-list upon encountering CSP errors.
  • The experiment was conducted using GPT-5.5 xhigh in the Codex desktop app.
  • Tags associated with the experiment include content-security-policy, iframes, and security.

Analysis

This experiment is significant as it addresses common challenges faced by developers when dealing with CSP errors, providing a user-friendly solution to enhance web application security. By allowing users to easily add domains to an allow-list, it streamlines the process of managing CSP restrictions and improves overall user experience.

Conclusion

IT professionals should consider implementing similar mechanisms in their applications to facilitate user interaction with CSP policies, thereby enhancing security while maintaining usability. Experimenting with custom fetch() functions could lead to innovative solutions in web security management.