Set Password Strength Minimum Lowercase Characters

An XCCDF Rule

Description

The pam_cracklib module's lcredit= parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_cracklib will grant +1 additional length credit for each lowercase character. Add lcredit=-1 after pam_cracklib.so to require use of a lowercase character in passwords.

Rationale

Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.

ID: xccdf_org.ssgproject.content_rule_cracklib_accounts_password_pam_lcredit
Severity: Medium
References: CCI-000193

IA-5(1)(a) IA-5(1).1(v)

Req-8.2.3

8.3.6

SRG-OS-000070-GPOS-00038

SLES-15-020140

5.3.1

SV-234883r622137_rule

CCE-85676-5

BP28(R18)
Updated: about 1 year ago

- name: XCCDF Value var_password_pam_lcredit # promote to variable
  set_fact:
    var_password_pam_lcredit: !!str <xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_password_pam_lcredit" use="legacy"/>
  tags:
    - always
- name: Set control_flag fact
  set_fact:
    control_flag: requisite
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Check to see if 'pam_cracklib.so' module is configured in '/etc/pam.d/common-password'
  shell: |
    set -o pipefail
    grep -E '^\s*password\s+\S+\s+pam_cracklib.so' /etc/pam.d/common-password || true
  register: check_pam_module_result
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Configure 'pam_cracklib.so' module in '/etc/pam.d/common-password'
  lineinfile:
    path: /etc/pam.d/common-password
    line: password requisite pam_cracklib.so
    state: present
  when: '"pam_cracklib.so" not in check_pam_module_result.stdout'
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Ensure 'pam_cracklib.so' module has conforming control flag
  lineinfile:
    path: /etc/pam.d/common-password
    regexp: ^(\s*password\s+)\S+(\s+pam_cracklib.so\s+.*)
    line: \g<1>requisite\g<2>
    backrefs: true
  when: control_flag|length
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Ensure "pam_cracklib.so" module has argument "lcredit={{ var_password_pam_lcredit
    }}"
  lineinfile:
    path: /etc/pam.d/common-password
    regexp: ^(\s*password\s+requisite\s+pam_cracklib.so(?:\s+\S+)*\s+lcredit=)(?:\S+)((\s+\S+)*\s*\\*\s*)$
    line: \g<1>{{ var_password_pam_lcredit }}\g<2>
    backrefs: true
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Check the presence of "lcredit" argument in "pam_cracklib.so" module
  shell: |
    set -o pipefail
    grep -E '^\s*password\s+requisite\s+pam_cracklib.so.*\s+lcredit(=|\s|\s*$)' /etc/pam.d/common-password || true
  register: check_pam_module_argument_result
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Add "lcredit" argument to "pam_cracklib.so" module
  lineinfile:
    path: /etc/pam.d/common-password
    regexp: ^(\s*password\s+requisite\s+pam_cracklib.so)((\s+\S+)*\s*(\\)*$)
    line: \g<1> lcredit={{ var_password_pam_lcredit }}\g<2>
    backrefs: true
  when: '"lcredit" not in check_pam_module_argument_result.stdout'
  tags:
  - CCE-85676-5
  - DISA-STIG-SLES-15-020140
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(1).1(v)
  - PCI-DSS-Req-8.2.3
  - PCI-DSSv4-8.3.6
  - cracklib_accounts_password_pam_lcredit
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy


declare -a VALUES=()
declare -a VALUE_NAMES=()
declare -a ARGS=()
declare -a NEW_ARGS=()
var_password_pam_lcredit='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_password_pam_lcredit" use="legacy"/>'

VALUES+=("$var_password_pam_lcredit")
VALUE_NAMES+=("lcredit")
ARGS+=("")
NEW_ARGS+=("")

for idx in "${!VALUES[@]}"
do
    if [ -e "/etc/pam.d/common-password" ] ; then
        valueRegex="${VALUES[$idx]}" defaultValue="${VALUES[$idx]}"
        # non-empty values need to be preceded by an equals sign
        [ -n "${valueRegex}" ] && valueRegex="=${valueRegex}"
        # add an equals sign to non-empty values
        [ -n "${defaultValue}" ] && defaultValue="=${defaultValue}"

        # fix the value for 'option' if one exists but does not match 'valueRegex'
        if grep -q -P "^\\s*password\\s+requisite\\s+pam_cracklib.so(\\s.+)?\\s+${VALUE_NAMES[$idx]}(?"'!'"${valueRegex}(\\s|\$))" < "/etc/pam.d/common-password" ; then
            sed --follow-symlinks -i -E -e "s/^(\\s*password\\s+requisite\\s+pam_cracklib.so(\\s.+)?\\s)${VALUE_NAMES[$idx]}=[^[:space:]]*/\\1${VALUE_NAMES[$idx]}${defaultValue}/" "/etc/pam.d/common-password"

        # add 'option=default' if option is not set
        elif grep -q -E "^\\s*password\\s+requisite\\s+pam_cracklib.so" < "/etc/pam.d/common-password" &&
                grep    -E "^\\s*password\\s+requisite\\s+pam_cracklib.so" < "/etc/pam.d/common-password" | grep -q -E -v "\\s${VALUE_NAMES[$idx]}(=|\\s|\$)" ; then

            sed --follow-symlinks -i -E -e "s/^(\\s*password\\s+requisite\\s+pam_cracklib.so[^\\n]*)/\\1 ${VALUE_NAMES[$idx]}${defaultValue}/" "/etc/pam.d/common-password"
        # add a new entry if none exists
        elif ! grep -q -P "^\\s*password\\s+requisite\\s+pam_cracklib.so(\\s.+)?\\s+${VALUE_NAMES[$idx]}${valueRegex}(\\s|\$)" < "/etc/pam.d/common-password" ; then
            echo "password requisite pam_cracklib.so ${VALUE_NAMES[$idx]}${defaultValue}" >> "/etc/pam.d/common-password"
        fi
    else
        echo "/etc/pam.d/common-password doesn't exist" >&2
    fi
done

for idx in "${!ARGS[@]}"
do
    if ! grep -q -P "^\s*password\s+requisite\s+pam_cracklib.so.*\s+${ARGS[$idx]}\s*$" /etc/pam.d/common-password ; then
        sed --follow-symlinks -i -E -e "s/^\\s*password\\s+requisite\\s+pam_cracklib.so.*\$/& ${NEW_ARGS[$idx]}/" /etc/pam.d/common-password
    fi
done

Set Password Strength Minimum Lowercase Characters

Description

Rationale

Remediation - Ansible

Remediation - Shell Script