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Referrer Policy

DevOps & Security
referrer-policy

Referrer Policy is an Agent Skill for devops & security published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Use when reviewing HTTP response headers for privacy hardening on any website that handles authentication, session state, or sensitive URL parameters.

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How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/referrer-policy/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/referrer-policy, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Set a Referrer-Policy header

Without a Referrer-Policy, a password reset link like https://example.com/reset?token=abc123 is included in the Referer header when the user clicks an external link on that page — leaking the token to third parties.

Quick Reference

  • Use Referrer-Policy: strict-origin-when-cross-origin — the recommended modern default
  • strict-origin-when-cross-origin sends the full URL for same-origin requests, only the origin for cross-origin HTTPS, and nothing for HTTPS→HTTP
  • Never use unsafe-url — it sends the full URL including path and query string to every external site
  • Can be set via HTTP header, <meta> tag, or the referrerpolicy attribute on individual <a> and <img> elements
  • Sensitive URLs (reset tokens, private IDs) in query strings can be exposed via the Referer header if policy is too permissive

Check

Check whether the server sends a Referrer-Policy header and verify the value is appropriate. The recommended value is strict-origin-when-cross-origin. Check for any pages with sensitive URL parameters that could be leaked via the Referer header.

Fix

Add Referrer-Policy: strict-origin-when-cross-origin to all HTTP responses. Configure it in your web server, CDN, or application framework. For pages with particularly sensitive URLs, consider no-referrer or same-origin.

Explain

Explain what the Referer header contains, how a permissive Referrer-Policy can leak sensitive URL parameters to third parties, and what the difference is between the various Referrer-Policy values.

Code Review

Review server config, headers, forms, and integration points related to Set a Referrer-Policy header. Flag exact responses, cookies, or browser behaviors that violate the rule, and verify them against the effective production-like response.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/security/referrer-policy