Budibase versions 3.39.4 before 3.40.0 contain an authorization regression in the S3 attachment upload endpoint that allows BASIC users to obtain S3 PutObject presigned URLs by sending POST requests to the attachments endpoint. The route was changed from a BUILDER permission check to a TABLE/WRITE check, which BASIC users hold by default. Attackers can specify arbitrary S3 buckets in the request body to generate presigned URLs for writing to any bucket accessible by the stored IAM credentials, enabling unauthorized file uploads.