Content Security Policy: Are you worried about the security of your website’s content? Concerned about potential data breaches and vulnerabilities? Don’t fret; we’ve got your back! In this blog post, we’ll walk you through the essential aspects of Content Security Policy (CSP) with our easy-to-follow CSP Cheat Sheet. By the end of this read, you’ll have a solid understanding of CSP and how to use it to safeguard your data effectively.

Understanding Content Security Policy (CSP)

What is CSP?

Content Security Policy (CSP) is a vital security feature that helps protect your website from various types of attacks, including Cross-Site Scripting (XSS) and data injection attacks. It acts as a set of rules that instruct the browser on which resources are allowed to load and execute, mitigating the risk of malicious code execution.

The CSP Cheat Sheet: Quick Reference Guide

1. Setting Up CSP

Before diving into the specifics, let’s set up CSP on your website. You can do this by adding the following HTTP header to your web server configuration:

Content-Security-Policy: directives;

Replace ‘directives’ with your desired security rules. For example, to allow only resources from your own domain, use:

Content-Security-Policy: default-src 'self';

2. Defining Sources

‘self’: Refers to the current domain.

‘unsafe-inline’: Allows inline scripts and styles (use with caution).

‘unsafe-eval’: Allows code execution through eval() (use with caution).

‘https://’: Specify trusted domains explicitly.

3. Restricting External Sources

To prevent data leaks and unauthorized resource loading, use directives like img-src, script-src, and style-src. For instance:

img-src 'self' https://trusted-domain.com;
script-src 'self' 'unsafe-inline';
style-src 'self' 'unsafe-inline' https://trusted-css.com;

4. Reporting Violations

Enable CSP violation reporting to stay informed about security breaches. Add a report-uri directive:

Content-Security-Policy-Report-Only: default-src ‘self’; report-uri /csp-report-endpoint;

5. Use a CSP Builder Tool

There are many online tools available to generate CSP rules for your website. Some popular ones include CSP Evaluator and Mozilla’s CSP Generator.

Certainly! Let’s dive deeper into Content Security Policy (CSP) and explore some practical examples of how to implement CSP directives to protect your website effectively.

Examples of Common CSP Directives

1. Allowing Resources from Trusted Sources Only

One of the primary functions of CSP is to specify which domains are allowed to load resources on your website. To achieve this, use the default-src directive:

Content-Security-Policy: default-src ‘self’ trusted-domain.com cdn.anotherdomain.net;

In this example, resources from ‘self’ (your domain) and ‘trusted-domain.com’ are allowed, along with ‘cdn.anotherdomain.net’.

2. Preventing Inline Script Execution

To mitigate XSS attacks, you can restrict the execution of inline scripts and event handlers. Here’s how to do it:

Content-Security-Policy: script-src ‘self’;

This directive allows scripts to execute only from the same origin (‘self’). Any inline scripts will be blocked.

3. Allowing Inline Styles with Nonces

If you need to allow inline styles (although it’s generally discouraged due to security risks), you can do so using a nonce:

Content-Security-Policy: style-src ‘self’ ‘nonce-randomNonceValueHere’;

Remember to generate a unique nonce value for each page load and include it in your inline <style> tags:

<style nonce="randomNonceValueHere">
/* Your inline styles here */
</style>

4. Loading Resources via Secure Connections

Enforce secure connections for loading resources to protect against mixed content issues:

Content-Security-Policy: upgrade-insecure-requests;

This directive ensures that all resources are loaded via HTTPS, even if the page is served over HTTP.

5. Reporting Violations to a Specific Endpoint

To receive reports about CSP violations, set up a reporting endpoint:

Content-Security-Policy-Report-Only: default-src ‘self’; report-uri /csp-report-endpoint;

Reports will be sent to ‘/csp-report-endpoint’, allowing you to monitor and address potential security issues.

Testing Your CSP Implementation

Before deploying CSP on your live website, it’s essential to test it thoroughly to avoid unintended consequences. You can use the browser’s developer tools to check for CSP violation reports and adjust your policy accordingly.