AWS S3 Bucket CORS Header Missing for Web Uploads

VERIFIED WAYPOINT ⚡ Saves ~42,000 tokens ($0.15) Category: Cloud & Storage

🎯 Target Goal & Friction

Goal: Configure S3 bucket CORS for presigned client uploads

Error Signature: Access to fetch at 'https://s3.amazonaws.com/...' from origin has been blocked by CORS policy

⚡ Direct Teleport Deep Link (0ms Navigation)

https://s3.console.aws.amazon.com/s3/buckets/{bucket_name}?tab=permissions →

Agents skip UI exploration menus by navigating directly to this endpoint.

Verified Code / Configuration Diff

@@ S3 CORS JSON @@
+ [
+   {
+     "AllowedHeaders": ["*"],
+     "AllowedMethods": ["GET", "PUT", "POST", "HEAD"],
+     "AllowedOrigins": ["*"],
+     "ExposeHeaders": ["ETag"]
+   }
+ ]

1-Line Instant CLI Fix

aws s3api put-bucket-cors --bucket {bucket_name} --cors-configuration file://cors.json

Root Cause & Explanation

Direct browser uploads to S3 presigned URLs require explicit CORS configuration on the bucket permissions tab.