Find resources loaded over unencrypted HTTP within HTTPS pages, a problem called mixed content. Review resource URLs and security headers, then guide HTTPS replacements and automatic request upgrades to address blocked or insecure resources.
Use when reviewing an HTTPS page for resources (scripts, images, stylesheets, iframes) that are loaded over plain HTTP.
Review the instructions the agent will receive before you install.
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.
upgrade-insecure-requests CSP directive to automatically upgrade HTTP sub-resources to HTTPShttp:// URLs in HTML, CSS, and JavaScriptContent-Security-Policy: upgrade-insecure-requests directive is the most practical fix for legacy contentScan 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.
Replace all http:// resource URLs with https:// equivalents. If the resource provider does not support HTTPS, host the resource yourself or find an alternative. Add Content-Security-Policy: upgrade-insecure-requests as a safety net for any remaining HTTP URLs.
Explain the difference between active and passive mixed content, why active mixed content is blocked by browsers, and how the upgrade-insecure-requests CSP directive works.
Review server config, headers, forms, and integration points related to Avoid mixed content on HTTPS pages. Flag exact responses, cookies, or browser behaviors that violate the rule, and verify them against the effective production-like response.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/rules/security/mixed-content
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