Video Thumbnails & DNS: Are They Linked?

TL;DR

Animated video thumbnails often use different servers than the actual videos themselves for serving images/animations. This means their DNS records won’t necessarily match the video’s. Here’s how to check and what it means.

Checking Thumbnail & Video DNS Records

1. Find the Video URL: Get the direct link to the video you want to investigate.
2. Inspect the Thumbnail Image Source: Right-click on the thumbnail (on the website where it’s displayed) and select ‘Copy image address’ or similar. This is the URL for the thumbnail.
   • If it’s a GIF, this will be a direct link to the animated file.
   • For other formats, it might point to an image server.
3. Use nslookup or dig to find DNS records: These tools query DNS servers.

   nslookup example.com

   dig example.com

   Replace ‘example.com’ with the video URL and thumbnail image source URL respectively.

4. Compare the Results: Look at the IP addresses returned for both URLs.
   • If they are different, the thumbnail is served from a separate server.
   • Pay attention to the record types (A, CNAME, etc.). A CNAME pointing to a different domain confirms separate servers.

Why Thumbnails Use Different DNS

1. Content Delivery Networks (CDNs): Video platforms often use CDNs for both videos and thumbnails, but they might use *different* CDNs for each.
   • Thumbnails are smaller files and can be cached more aggressively on a different CDN.
   • Different geographical locations may use separate CDN endpoints for optimal performance.
2. Image Hosting Services: Thumbnails might be hosted on dedicated image hosting services (e.g., Imgur, Cloudinary) that have their own DNS records.
3. Separate Infrastructure: The video platform may intentionally separate thumbnail serving infrastructure for scalability and resilience.

What Does This Mean for cyber security?

1. Third-Party Risk: If thumbnails are served from a third-party domain, you’re relying on their security practices.
   • A compromised thumbnail server could potentially deliver malicious content.
   • Consider the reputation of the image hosting service.
2. Tracking: Different DNS records can indicate different tracking mechanisms being used for videos and thumbnails.
3. Content Integrity: While not a direct security threat, differing DNS could suggest potential manipulation or alteration of the thumbnail content (though this is rare).

Tools to Help

• Browser Developer Tools: Use your browser’s developer tools (usually F12) to inspect network requests and see where thumbnails are loaded from.
• Online DNS Lookup Tools: Many websites offer free DNS lookup services if you prefer a graphical interface.
  What’s My DNS is one example.