Which of the following should be used with caution because of its ability to provide access to block level data instead of file level data?

CIFS (Common Internet File System) is a file-level protocol that provides access to files and directories, not raw block data.

NFS (Network File System) is also a file-level protocol that presents data as files managed by a remote file system, not as raw blocks.

iSCSI (Internet Small Computer Systems Interface) encapsulates SCSI commands over TCP/IP to provide block-level storage access, meaning a client can read and write raw disk blocks without any file system mediation. This is more dangerous than file-level protocols because an unauthorized client gaining iSCSI access can overwrite partition tables, bypass file permissions, and access data from any volume on the target. Unlike file-level protocols, there is no layer of access control enforced by a file system between the client and the raw data.

NAS (Network Attached Storage) is a storage device category that typically uses file-level protocols such as NFS or CIFS, not block-level access.