A mixed content warning means an HTTPS page is requesting at least one resource over plain HTTP. Fix it by finding the exact HTTP request in your browser’s developer tools, serving that resource over HTTPS, replacing the URL in your code or CMS, and then checking the whole site for remaining references. Do not rely on a redirect alone: every resource request must be secure.
What mixed content is
When a document loads over https:// but requests an image, stylesheet, script, frame, font, API response or other resource over http://, the page contains mixed content. The main page may have a valid certificate while one of its subrequests remains vulnerable to interception.
The problem is both confidentiality and integrity. Someone who can tamper with the HTTP response could replace a script, alter a stylesheet, substitute an image, inject misleading text or change a download. That is why browsers treat executable resources more severely than ordinary media.
Active and passive resources
| Resource type | Typical examples | Browser response | Risk |
|---|---|---|---|
| Active (blockable) | JavaScript, stylesheets, frames, fonts, API and WebSocket connections | Usually blocked when requested over HTTP | Modification can execute code or change page behavior |
| Passive (upgradable) | Images and some audio or video | May be rewritten to HTTPS automatically | Still fails if no HTTPS equivalent exists; users may see missing media |
Exact wording and behavior differ by browser release. Treat the developer console for the affected page as authoritative.
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Why the warning appears
Hard-coded URLs after an SSL migration
Templates, database fields, feeds and source files often retain URLs such as http://cdn.example.com/app.js after the site itself moved to HTTPS. Search your repository and content database, not only the page source.
CSS and JavaScript-generated requests
A page can look clean in its HTML while a stylesheet contains background-image: url(http://...), or JavaScript constructs an HTTP endpoint at runtime. Inspect network requests and search scripts for URL fragments.
Third-party embeds and CDNs
Advertising, analytics, video players, fonts, chat widgets and iframe providers may still publish HTTP endpoints. Use the provider’s HTTPS endpoint or replace the integration. A provider redirecting HTTP to HTTPS is less reliable than changing your code to call HTTPS directly.
Forms, downloads and navigation
Form actions, iframe sources, download links and redirects can also create warnings. Mixed downloads are especially risky because a file can be changed in transit even when the page containing the link was secure.
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APIs, WebSockets and redirects
XHR or fetch() calls to HTTP APIs are active mixed content. Use https:// and, for WebSockets, wss://. Check redirect chains: a secure-looking URL that responds with a redirect to HTTP still produces an insecure request.
Diagnose the exact request
- Open the affected HTTPS page.
- Open Developer Tools (usually F12 or Ctrl+Shift+I), then select Console.
- Reload with the console open. Read the mixed-content message and copy the requesting page, resource type and complete URL.
- Open the Network panel, reload, and filter for
http://, blocked requests or failed status codes. Inspect the initiator column to locate the HTML, CSS or script that created the request. - Repeat on representative templates: home page, product or article page, checkout, login, forms and pages behind authentication.
One page scan is not enough. A recursive crawler or mixed-content checker can find URLs hidden in CSS, JavaScript, feeds, CMS fields and rarely visited templates. Also inspect generated emails and downloadable documents if they contain links.
Permanent fix: a repeatable workflow
1. Make the resource available over HTTPS
Install a valid certificate on the resource’s host, serve the same path over HTTPS, and verify the certificate chain, hostname and TLS configuration. Test the final URL directly and inspect every redirect hop.
2. Replace insecure references
Change same-site references to https:// or a safe relative URL such as /assets/app.css. Update all layers:
- HTML templates and canonical or alternate links
- CSS
url()values - JavaScript, JSON configuration and API base URLs
- CMS content, custom fields and page-builder blocks
- Forms, iframes, downloads and feeds
- Environment variables used in staging and production
Do not use protocol-relative URLs such as //cdn.example.com/file.js as a new fix; explicit HTTPS is clearer and avoids insecure behavior in non-HTTPS contexts.
3. Correct third-party integrations
Read the provider’s current embed documentation and change the endpoint to HTTPS. If the provider cannot serve the required asset securely, remove or replace it. Do not weaken your page’s security policy to preserve an obsolete widget.
4. Check redirects and application configuration
Configure HTTP-to-HTTPS redirects at the origin, but keep source URLs secure. Check reverse proxies, load balancers, CDN origin settings and framework URL-generation settings so they recognize the original HTTPS scheme. Incorrect proxy headers commonly cause applications to generate HTTP links after termination at a TLS proxy.
5. Crawl and deploy safely
Run a site-wide crawl after the code and content changes. Clear CDN and application caches, then test logged-in and logged-out versions. Recheck console and network logs on every important template before declaring the migration complete.
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Add the response header Content-Security-Policy: upgrade-insecure-requests when you need browsers to rewrite eligible legacy HTTP resource requests to HTTPS before sending them. It also applies to same-origin top-level navigations, nested browsing-context navigations and form submissions.
This directive is a safety net, not a substitute for correcting source URLs. It cannot upgrade a top-level navigation to a different origin, and it cannot make a host that lacks HTTPS work. Monitor reports and remove legacy references from your code and content.
Do not rely on the deprecated directive
block-all-mixed-content is deprecated for new projects. Modern browsers already upgrade eligible passive content and block other mixed content, so focus on eliminating HTTP URLs and deploying a correct policy.
HSTS and the limits of CSP
HTTP Strict Transport Security (HSTS) tells a browser to use HTTPS for future connections to your domain. It helps users who follow an old HTTP link or a third-party link and reduces exposure to SSL-stripping attacks. CSP upgrade-insecure-requests handles requests made by a page; HSTS protects the initial connection to the site. Use HSTS only after HTTPS works reliably across the domain and its subdomains, because a browser honoring the policy will refuse HTTP access.
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Common symptoms and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| Script or stylesheet is blocked | Active HTTP URL | Change the source to HTTPS and verify the host serves the file securely. |
| Images appear intermittently or are missing | Automatic upgrade found no HTTPS equivalent, or the HTTPS path returns an error | Test the upgraded URL directly; fix the certificate, path or hosting. |
| Only one browser reports a warning | Different browser version or handling of upgradable content | Use that browser’s console and network log; remove the HTTP reference rather than targeting one browser. |
| Everything is HTTPS in page source | CSS, JavaScript, iframe or redirect creates the request later | Use Network initiators and search bundled assets and runtime configuration. |
| API calls fail after enabling SSL | HTTP API or WebSocket endpoint | Use HTTPS or wss://, configure CORS for the secure origin, and update environment variables. |
| Form submission warning | HTTP form action | Change the action to HTTPS and verify the destination accepts secure POST requests. |
Performance, reliability and operational notes
- HTTPS does not make an unavailable resource available. A migrated URL can still fail because of DNS, certificate, path, authorization or CORS errors.
- Redirects add latency and can expose legacy requests before the final URL is reached. Point applications directly at HTTPS.
- Check third-party assets during vendor changes; an integration can reintroduce mixed content without a code deployment.
- Test cache keys and CDN behavior after changing schemes. Purge stale HTTP variants where necessary.
- Use automated source scans in CI, plus a periodic authenticated crawl, because runtime-only URLs and restricted pages are easy to miss.
Verify the repair with screenshots (optional)
Capture the page before and after deployment and compare the console or rendered result at the same viewport. A screenshot does not replace console and network inspection, but it provides a useful visual regression record for missing images, broken embeds and layout changes.
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FAQ
Will changing every URL to HTTPS always fix the warning?
Only if the destination has a valid certificate, serves the requested path and does not redirect back to HTTP. Confirm the complete request chain in Network tools.
Can I ignore a warning for an image?
No. The browser may upgrade it today, but the HTTPS equivalent can fail and behavior can change. Replace the HTTP URL permanently.
Does HSTS repair old HTTP links in my database?
No. HSTS affects browser connections; it does not rewrite stored HTML, CSS, JavaScript or CMS content. Correct those references and use HSTS as transport protection.
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