CVE-2026-71415: Kirby: File upload permissions are not checked during processing of chunk data

In affected releases, the chunk upload handler did not check for the user’s file upload permissions before storing incomplete chunk data in the temporary directory.

This allowed attackers without upload permissions to upload multiple large files in chunks. If the final chunk was never provided, Kirby would keep the incomplete files for 24 hours. This could cause attacker-controlled storage consumption until the temporary files were automatically cleaned up or manually removed, potentially preventing other users from uploading files, or site logic from storing data.