How to Fix Game Assets Blocked by CORS When Served From a CDN

Splitting assets onto a CDN adds an origin boundary, and the browser enforces it per resource type. The fix lives in the CDN config. Here is the setup that works.

How to fix it

1. Set the headers at the source

Configure Access-Control-Allow-Origin (your domain or *) on the bucket/CDN for game asset paths — S3/B2/Cloudflare all support per-bucket or per-route CORS rules; propagate/purge caches after changing.

2. Match request modes to needs

fetch() for JSON/binary defaults to CORS mode and needs the headers; images/audio via elements need crossorigin="anonymous" only if they feed canvas/WebGL/WebAudio analysis.

3. Watch the preflight

Custom headers (auth, content-type json on POST) trigger OPTIONS preflights — the CDN must answer them (allowed methods/headers) or the real request never happens.

4. Verify with the console and curl

The console names the missing header precisely; curl -H "Origin: https://yourgame.com" -I asset-url shows what the CDN actually returns — test after every cache purge.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.