Vulnerability Discussion

Restricting TFTP to a specific directory prevents remote users from copying, transferring, or overwriting system files.

Check

Note: If TFTP is not required, it should not be installed. If TFTP is not installed, this rule is not applicable.

Determine if TFTP server is installed with the following command:

$ sudo dnf list installed | grep tftp-server
tftp-server.x86_64 x.x-x.el8

Verify that the TFTP daemon, if tftp.server is installed, is configured to operate in secure mode with the following command:

$ grep -i execstart /usr/lib/systemd/system/tftp.service
ExecStart=/usr/sbin/in.tftpd -s /var/lib/tftpboot

If TFTP is installed and is not documented with the information system security officer (ISSO) as an operational requirement, this is a finding.

Note: The "-s" option ensures that the TFTP server only serves files from the specified directory, which is a security measure to prevent unauthorized access to other parts of the file system.

Fix

Configure the TFTP daemon to operate in secure mode with the following command:
$ sudo systemctl edit tftp.service

In the editor enter:
[Service]
ExecStart=/usr/sbin/in.tftpd -s /var/lib/tftpboot

After making changes, reload the systemd daemon and restart the TFTP service as follows:
$ sudo systemctl daemon-reload
$ sudo systemctl restart tftp.service