CSP Header Configuration Checklist

Learn how to configure Content Security Policy headers to enhance your website's security against threats like XSS attacks.

By Midday Staff
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7
Minute Read

CSP headers are your website's security guard, ensuring only trusted resources load. Here's what you need to know:

Quick Setup:

  1. Use directives like default-src 'self' to allow resources only from your domain.
  2. Add specific rules for scripts, styles, images, and more.
  3. Enable violation reporting to monitor and refine your policy.

Pro Tip: Start with Report-Only mode to test without blocking content. Regularly review reports to improve your CSP.

CSP headers are essential for modern web security. Ready to safeguard your site? Let’s dive in.

Before You Start: CSP Setup Requirements

Website Resource List

Organize your website's resources to avoid blocking important content.

1. Document External Resources

Create a list of all third-party resources your site relies on, such as:

2. Map Internal Resources

Identify and list all resources hosted on your own servers, including:

3. Review Integration Points

Catalog all integration points your website uses, such as:

Security Goals Assessment

Evaluate your security needs based on the following:

Risk Level Assessment

Feature Requirements

Setup Method Selection

Pick the setup method that matches your deployment needs:

Feature HTTP Headers Meta Tags
Browser Support Works across all modern browsers Limited in older browsers
Implementation Requires server-side configuration Client-side, no server changes
Flexibility Adjustable without redeploying code Requires code deployment
Report-URI Support Full support for reporting violations Limited reporting options
Load Time Impact Sent before content loads Processed after HTML parsing

Key Points to Consider:

Keep these essentials in mind as you set up CSP headers.

CSP Header Setup Steps

Basic Directives Setup

Set up the main Content Security Policy (CSP) directives directly in your server configuration or application code:

Extra Directives Setup

Once the basic setup is complete, you can add more specific directives to improve security:

Directive Purpose Example Value
font-src Controls font loading 'self' https://fonts.gstatic.com
frame-src Manages frame embedding 'self' https://trusted-frames.com
media-src Restricts media sources 'self' https://media-cdn.com
object-src Blocks plugin content 'none'
script-src Prevents inline scripts 'self' 'nonce-randomString123'

Violation Reporting Setup

To monitor and fine-tune your policy, set up violation reporting:

  1. Define a reporting endpoint: Use the report-uri directive to specify where violation reports should be sent. 
    report-uri https://your-domain.com/csp-reports;
  2. Test with Report-Only mode: During testing, enable this mode to log violations without enforcing the policy: 
    Content-Security-Policy-Report-Only: default-src 'self';
  3. Log detailed reports: Configure your violation handler to capture key information such as:
    • Timestamp
    • Blocked resource URL
    • Violated directive
    • User agent
    • Page URL

Analyzing these reports helps you identify legitimate resources to whitelist while ensuring strong security. Regularly reviewing this data will also minimize false positives that could disrupt the user experience.

CSP Header Verification

Test Mode Setup

To monitor violations without blocking content, enable the Content-Security-Policy-Report-Only mode. This allows you to log issues for analysis:

Content-Security-Policy-Report-Only: default-src 'self'; report-uri /csp-violations;

Here's an example configuration:

Content-Security-Policy-Report-Only: 
    default-src 'self';
    report-uri /csp-violations;
    report-to csp-endpoint;

Once logging is enabled, use the collected data for further analysis as outlined below.

Violation Report Analysis

When reviewing CSP violation reports, focus on the following key areas:

Element What to Check Suggested Action
Blocked URL Source of the resource Allow trusted sources in the policy
Directive Specific policy rule Adjust the scope of the directive
Agent Browser and version info Verify browser compatibility
Time When the issue occurred Look for recurring patterns
Page Affected page or section Pinpoint problematic areas

Policy Updates

Use the insights from your analysis to regularly update and fine-tune your CSP policy. Here's how to approach this:

Always apply changes in report-only mode first. This ensures that legitimate functionality remains unaffected while you test and refine your security measures.

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Conclusion

Key Takeaways

Next Steps

Put these insights into action by actively managing your Content Security Policy (CSP).

To keep your CSP effective over time, make it a habit to review your server configurations, code, cloud settings, and CDN setups. This will help you address vulnerabilities quickly and keep your site secure.

Content Security Policy: Zero to Hero

FAQs

How can I configure a CSP policy that balances strong security with allowing legitimate resources?

To create a Content Security Policy (CSP) that ensures strong security while avoiding unnecessary blocks on legitimate resources, follow these steps:

  1. Start with a default policy: Use a restrictive default-src 'none'; and explicitly allow only the resources you need, such as scripts, styles, images, or APIs.
  2. Whitelist trusted sources: Specify trusted domains for each resource type (e.g., script-src, img-src) to ensure only approved content is loaded.
  3. Use report-only mode for testing: Before enforcing the policy, enable Content-Security-Policy-Report-Only to monitor and fine-tune your settings without disrupting functionality.
  4. Review error logs: Analyze CSP violation reports to identify blocked resources and adjust your policy as needed.
  5. Regularly update your policy: As your application evolves, revisit your CSP to account for new resources or changes in functionality.

By carefully testing and iterating, you can maintain a secure CSP while minimizing disruptions to legitimate resources.

What are the pros and cons of using HTTP headers versus meta tags for implementing a Content Security Policy (CSP)?

Using HTTP headers for implementing a Content Security Policy (CSP) is generally more secure and reliable than using meta tags. HTTP headers are sent directly by the server and are harder to modify, making them less vulnerable to attacks. They also apply to all resources on a page, ensuring comprehensive protection.

On the other hand, meta tags are embedded in the HTML document, which can make them easier to modify if the page is compromised. Additionally, meta tags only apply to the specific document they are included in, which may result in inconsistent security coverage. While meta tags can be useful for testing or specific cases, HTTP headers are recommended for robust, site-wide CSP implementation.

How can I review and use CSP violation reports to strengthen my website's security?

To effectively analyze Content Security Policy (CSP) violation reports, start by collecting the reports generated by your website when a violation occurs. These reports typically include details about the blocked resource, the policy that was violated, and the URL where the issue happened.

Focus on identifying patterns or repeated violations, such as third-party scripts or resources that are not included in your CSP. Adjust your CSP rules to allow only trusted sources while blocking potentially harmful ones. Additionally, consider using tools or dashboards to organize and visualize the data for easier analysis. Regularly reviewing these reports helps you fine-tune your CSP and maintain a robust security posture.

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