How to fix missing content security policy on Magento Open Source

Steps for Magento Open Source

1. Same as Adobe Commerce above — CSP configuration is in Admin → Stores → Configuration → Security → Content Security Policy (available from Magento 2.3.5+).
2. Edit `csp_whitelist.xml` in your custom theme or module under `etc/` to add trusted external origins.
3. Set `restrict_mode` to `0` initially (report-only) then to `1` (enforce) in your XML or admin config once violations are resolved.
4. Flush cache: `bin/magento cache:flush` after changes.

Content-Security-Policy: default-src 'self'; script-src 'self' https://cdn.example.com; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' https://fonts.gstatic.com; object-src 'none'; frame-ancestors 'none'; base-uri 'self';

What is missing content security policy?

A Content Security Policy (CSP) is an HTTP response header your web server sends to a visitor's browser. It acts like a whitelist, telling the browser exactly which domains and sources are allowed to load scripts, stylesheets, images, fonts, and other content on your site. If a piece of code tries to load from a source not on your list — for example, a malicious script injected by an attacker — the browser simply refuses to run it. Without a CSP header, the browser has no such instructions and will run whatever code it finds on the page.

Without a CSP, your store is significantly more vulnerable to Cross-Site Scripting (XSS) and data-injection attacks — the #3 risk in the OWASP Top Ten. Attackers who find even a small vulnerability in a plugin, theme, or third-party widget can inject malicious scripts that steal customer payment card details, session cookies, or personal data directly from the browser (a technique known as "formjacking" or "Magecart"). A successful attack can result in PCI-DSS compliance failures, card-brand fines, regulatory penalties under GDPR or CCPA, and severe damage to customer trust. Search engines also consider site security as a ranking signal, and a compromised site can be blocklisted by Google, wiping out organic traffic overnight.

See the complete Missing content security policy guide for every platform and the full background.