Pappl-retrofit: directory traversal in the add-ppdfiles and delete-ppdfiles actions

A flaw was found in pappl-retrofit. The application fails to properly sanitize user-supplied filenames when handling the upload and deletion of PostScript Printer Description (PPD) files. A remote, unauthenticated attacker can exploit this directory traversal flaw by submitting filenames containing path traversal sequences. This allows the attacker to upload or delete arbitrary files on the system, which can result in data corruption, denial of service, or arbitrary command execution.