SV-257835r1155679: The Trivial File Transfer Protocol (TFTP) server must not be installed unless it is required, and if required, the RHEL 9 TFTP daemon must be configured to operate in secure mode. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

The Trivial File Transfer Protocol (TFTP) server must not be installed unless it is required, and if required, the RHEL 9 TFTP daemon must be configured to operate in secure mode.

Description

Discussion Text

Removing the "tftp-server" package decreases the risk of the accidental (or intentional) activation of tftp services. If TFTP is required for operational support (such as transmission of router configurations), its use must be documented with the information systems security manager (ISSM), restricted to only authorized personnel, and have access control rules established. Restricting TFTP to a specific directory prevents remote users from copying, transferring, or overwriting system files.

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-000366

References

DPMS Target Red Hat Enterprise Linux 9 DISA DPMS Target Red Hat Enterprise Linux 9 5551

Checks

DISA STIG (Manual Reference)

Verify if TFTP is installed, it is configured to operate in secure mode.

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

Check to see if TFTP server is installed with the following command:

$ sudo dnf list --installed tftp-server

Updating Subscription Management repositories.
Installed Packages
tftp-server.x86_64                             5.2-38.el9                              @rhel-9-for-x86_64-appstream-rpms

Verify 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

Note: The "-s" option ensures 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.

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

#!/bin/bash
# Reconstructed from oval:mil.disa.stig.rhel9os:def:257835
# The Trivial File Transfer Protocol (TFTP) server must not be installed unless it is required, and if required, the RHEL 9 TFTP daemon must be configured to operate in secure mode.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# /usr/lib/systemd/system/tftp.service: ExecStart has a -s option with a subdirectory assigned
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  grep -Pq '^ExecStart[ \t]*=[ \t]*\/usr\/sbin\/in\.tftpd[ \t]*-s[ \t]+/\S+[ \t]*$' '/usr/lib/systemd/system/tftp.service' &>/dev/null
}

if test_1; then
  echo "PASS"
else
  echo "FAIL"
fi

Assessment Script Powered by AISandbox-executed

A standalone Shell script to assess this control automatically. Review before running it in your environment.

Syntax-checked and actually executed in an isolated sandbox (not the real system this checks) — confirmed to run without errors.

#!/bin/sh
# OVAL definition: oval:mil.disa.stig.rhel9os:def:257835

if ! grep -qE '^ExecStart[ \t]*=[ \t]*\\/usr\\/sbin\\/in\\.tftpd[ \t]*-s[ \t]+/\\S+[ \t]*$' /usr/lib/systemd/system/tftp.service; then
    echo "FAIL"
    exit 1
fi

echo "PASS"
exit 0

Remediation

Configure RHEL 9 so that TFTP operates in secure mode if installed.

If TFTP server is not required, remove it with the following command:
$ sudo dnf -y remove tftp-server

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

If the "-s" option is not present in the "ExecStart" line or if the line is missing, this is a finding.