GHSA-8v25-v8p6-qf7v: rclone: Path traversal in serve s3 allows reading and overwriting root-level files

rclone serve s3 allows a client to read and write files at the root of the remote which would normally be inaccessible by using dot-dot path segments in the object key. It does not allow reading files outside of the root. A request such as GET /bucket/../root-secret.txt is handled as an object request for bucket “bucket”, but rclone normalizes the backend path and reads root-secret.txt from the serve root. The same issue also allows overwriting root-level files with PUT.