SV-214963r610931: The Ubuntu operating system must not be configured to allow blank or null passwords. | Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide

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Assessment Title

Rule Text

The Ubuntu operating system must not be configured to allow blank or null passwords.

Description

Discussion Text

If the operating system allows empty passwords, anyone could log on and run commands with the privileges. Empty passwords should never be used in operational environments.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000366V-75479SV-90159

References

DPMS Target Canonical Ubuntu 16.04 LTS DISA DPMS Target Canonical Ubuntu 16.04 LTS 4011

Checks

DISA STIG (Manual Reference)

To verify that null passwords cannot be used, run the following command: 

# grep pam_unix.so /etc/pam.d/* | grep nullok*
If this produces any output, it may be possible to log on with accounts with empty passwords.

If null passwords can be used, this is a finding.

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.ubuntu1604:def:121
# The Ubuntu operating system must not be configured to allow blank or null passwords.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# pam_unix.so does not have nullok as an option
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (grep -rhP --include='*' '^[^#]*pam_unix\.so\s+([^#]*).*$' '/etc/pam.d' | sed -En 's/^[^#]*pam_unix\.so\s+([^#]*).*$/\1/p') | grep -Pq '\bnullok(_secure)?\b'
}

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.ubuntu1604:def:121
check_pam_nullok() {
  local result=1
  for file in /etc/pam.d/*; do
    if [ -f "$file" ]; then
      if ! grep -qP "\bnullok(_secure)?\b" "$file"; then
        result=0
      fi
    fi
  done
  if [ $result -eq 0 ]; then
    echo "PASS"
    exit 0
  fi
}
echo "FAIL"
exit 1
check_pam_nullok

Remediation

Remove any instances of the "nullok" option in files under "/etc/pam.d/" to prevent logons with empty passwords.