CSP Generator

Generate Strict Content Security Policy Headers to Prevent XSS

Directive Configuration

default-srcFallback for all other directives

script-srcJavaScript execution privileges

style-srcCSS stylesheets

img-srcImages and favicons

connect-srcFetch, XHR, WebSockets

upgrade-insecure-requestsForce HTTP to HTTPS

Generated Policy

Raw Header Value

default-src 'self';

HTML Meta Tag

<meta http-equiv="Content-Security-Policy" content="default-src 'self';">

Next.js (next.config.js)

// next.config.js
module.exports = {
  async headers() {
    return [
      {
        source: '/(.*)',
        headers: [
          {
            key: 'Content-Security-Policy',
            value: "default-src 'self';"
          }
        ],
      },
    ]
  },
}

Nginx

add_header Content-Security-Policy "default-src 'self';" always;

or on-click handlers), which is exactly what XSS attacks exploit. 'unsafe-eval' allows the use of string-to-code execution functions like eval(), which can also be used to run malicious payloads. Avoiding these is critical for a strict and secure CSP."}},{"@type":"Question","name":"How does default-src work?","acceptedAnswer":{"@type":"Answer","text":"The default-src directive serves as a fallback for the other CSP fetch directives. If a specific directive like script-src or img-src is not explicitly defined in your policy, the browser will fall back to the rules defined in default-src. It is best practice to set default-src to 'self' or 'none' to enforce a default deny policy."}}]}

About CSP

What is a Content Security Policy (CSP)?

A Content Security Policy (CSP) is an added layer of security that helps detect and mitigate certain types of attacks, including Cross-Site Scripting (XSS) and data injection attacks. It works by restricting the domains that a browser should consider to be valid sources of executable scripts, stylesheets, and other resources.

Why shouldn't I use 'unsafe-inline' or 'unsafe-eval'?

Using 'unsafe-inline' allows the execution of inline scripts and styles (like <script>...</script> or on-click handlers), which is exactly what XSS attacks exploit. 'unsafe-eval' allows the use of string-to-code execution functions like eval(), which can also be used to run malicious payloads. Avoiding these is critical for a strict and secure CSP.

How does default-src work?

The default-src directive serves as a fallback for the other CSP fetch directives. If a specific directive like script-src or img-src is not explicitly defined in your policy, the browser will fall back to the rules defined in default-src. It is best practice to set default-src to 'self' or 'none' to enforce a default deny policy.

Engineering Guides

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