Ensure PAM Enforces Password Requirements - Maximum Consecutive Repeating Characters from Same Character Class

An XCCDF Rule

Description

The pam_pwquality module's maxclassrepeat parameter controls requirements for consecutive repeating characters from the same character class. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters from the same character class. Modify the maxclassrepeat setting in /etc/security/pwquality.conf to equal to prevent a run of ( + 1) or more identical characters.

Rationale

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex a password, the greater the number of possible combinations that need to be tested before the password is compromised.

ID: xccdf_org.ssgproject.content_rule_accounts_password_pam_maxclassrepeat
Severity: Medium
References: 1 12 15 16 5

DSS05.04 DSS05.05 DSS05.07 DSS05.10 DSS06.03 DSS06.10

CCI-000195

4.3.3.2.2 4.3.3.5.1 4.3.3.5.2 4.3.3.6.1 4.3.3.6.2 4.3.3.6.3 4.3.3.6.4 4.3.3.6.5 4.3.3.6.6 4.3.3.6.7 4.3.3.6.8 4.3.3.6.9 4.3.3.7.2 4.3.3.7.4

SR 1.1 SR 1.10 SR 1.2 SR 1.3 SR 1.4 SR 1.5 SR 1.7 SR 1.8 SR 1.9 SR 2.1

A.18.1.4 A.7.1.1 A.9.2.1 A.9.2.2 A.9.2.3 A.9.2.4 A.9.2.6 A.9.3.1 A.9.4.2 A.9.4.3

CM-6(a) IA-5(1)(a) IA-5(4) IA-5(c)

PR.AC-1 PR.AC-6 PR.AC-7

SRG-OS-000072-GPOS-00040

SV-230360r858777_rule
Updated: about 1 year ago

# Remediation is applicable only in certain platforms
if rpm --quiet -q pam; then

var_password_pam_maxclassrepeat='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_password_pam_maxclassrepeat" use="legacy"/>'





# Strip any search characters in the key arg so that the key can be replaced without
# adding any search characters to the config file.
stripped_key=$(sed 's/[\^=\$,;+]*//g' <<< "^maxclassrepeat")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "$var_password_pam_maxclassrepeat"

# If the key exists, change it. Otherwise, add it to the config_file.
# We search for the key string followed by a word boundary (matched by \>),
# so if we search for 'setting', 'setting2' won't match.
if LC_ALL=C grep -q -m 1 -i -e "^maxclassrepeat\\>" "/etc/security/pwquality.conf"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^maxclassrepeat\\>.*/$escaped_formatted_output/gi" "/etc/security/pwquality.conf"
else
    if [[ -s "/etc/security/pwquality.conf" ]] && [[ -n "$(tail -c 1 -- "/etc/security/pwquality.conf" || true)" ]]; then
        LC_ALL=C sed -i --follow-symlinks '$a'\\ "/etc/security/pwquality.conf"
    fi
    cce=""
    printf '# Per %s: Set %s in %s\n' "${cce}" "${formatted_output}" "/etc/security/pwquality.conf" >> "/etc/security/pwquality.conf"
    printf '%s\n' "$formatted_output" >> "/etc/security/pwquality.conf"
fi

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - DISA-STIG-RHEL-08-020140
  - NIST-800-53-CM-6(a)  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(4)
  - NIST-800-53-IA-5(c)
  - accounts_password_pam_maxclassrepeat
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
- name: XCCDF Value var_password_pam_maxclassrepeat # promote to variable
  set_fact:
    var_password_pam_maxclassrepeat: !!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_maxclassrepeat" use="legacy"/>
  tags:
    - always

- name: Ensure PAM Enforces Password Requirements - Maximum Consecutive Repeating
    Characters from Same Character Class - Ensure PAM variable maxclassrepeat is set
    accordingly
  ansible.builtin.lineinfile:
    create: true
    dest: /etc/security/pwquality.conf
    regexp: ^#?\s*maxclassrepeat
    line: maxclassrepeat = {{ var_password_pam_maxclassrepeat }}
  when: '"pam" in ansible_facts.packages'
  tags:
  - DISA-STIG-RHEL-08-020140
  - NIST-800-53-CM-6(a)
  - NIST-800-53-IA-5(1)(a)
  - NIST-800-53-IA-5(4)
  - NIST-800-53-IA-5(c)
  - accounts_password_pam_maxclassrepeat
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

Ensure PAM Enforces Password Requirements - Maximum Consecutive Repeating Characters from Same Character Class

Description

Rationale

Remediation - Shell Script

Remediation - Ansible