Avoid mixed content on HTTPS pages

Active mixed content (scripts loaded over HTTP into an HTTPS page) gives network attackers the ability to execute arbitrary JavaScript on your page — the same power as XSS, despite the page itself being served over HTTPS.

Quick Reference

• Active mixed content (scripts, iframes, stylesheets) is blocked outright by all modern browsers
• Passive mixed content (images, audio, video) triggers a security warning and may be upgraded or blocked
• Use upgrade-insecure-requests CSP directive to automatically upgrade HTTP sub-resources to HTTPS
• Audit all hardcoded http:// URLs in HTML, CSS, and JavaScript
• The Content-Security-Policy: upgrade-insecure-requests directive is the most practical fix for legacy content

Check

Scan the page source and network requests for any HTTP resources loaded on an HTTPS page. Check <script src>, <img src>, <link href>, <iframe src>, and CSS url() values for http:// URLs. Also check the Content-Security-Policy header for the upgrade-insecure-requests directive.

Fix

Replace all http:// resource URLs with https:// equivalents. If the resource provider does not support HTTPS, host the resource yourself…