Parse Server: File upload Content-Type override via extension mismatch

Impact

A file can be uploaded with a filename extension that passes the file extension allowlist (e.g., .txt) but with a Content-Type header that differs from the extension (e.g., text/html). The Content-Type is passed to the storage adapter without consistency validation. Storage adapters that store and serve the provided Content-Type (such as S3 or GCS) serve the file with the mismatched Content-Type. The default GridFS adapter is not affected because it derives Content-Type from the filename at serving time.

Patches

The file upload now derives the Content-Type from the filename extension, overriding any user-provided Content-Type when the file has an extension.

Workarounds

Configure the storage adapter or CDN to derive Content-Type from the filename extension instead of using the stored Content-Type.