Set number of Password Hashing Rounds - system-auth

An XCCDF Rule

Description

Configure the number or rounds for the password hashing algorithm. This can be accomplished by using the rounds option for the pam_unix PAM module.

In file /etc/pam.d/system-auth append rounds= to the pam_unix.so entry, as shown below:

password sufficient pam_unix.so ...existing_options... rounds=

The system's default number of rounds is 5000.

warning alert: Performance Warning

Setting a high number of hashing rounds makes it more difficult to brute force the password, but requires more CPU resources to authenticate users.

Rationale

Using a higher number of rounds makes password cracking attacks more difficult.

ID: xccdf_org.ssgproject.content_rule_accounts_password_pam_unix_rounds_system_auth
Severity: Medium
References: BP28(R68)

CCI-000196

SRG-OS-000073-GPOS-00041
Updated: over 1 year ago

Remediation Templates

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - accounts_password_pam_unix_rounds_system_auth
  - configure_strategy  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
- name: XCCDF Value var_password_pam_unix_rounds # promote to variable
  set_fact:
    var_password_pam_unix_rounds: !!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_unix_rounds" use="legacy"/>
  tags:
    - always
- name: Set number of Password Hashing Rounds - system-auth - Check if /etc/pam.d/system-auth
    file is present
  ansible.builtin.stat:
    path: /etc/pam.d/system-auth
  register: result_pam_file_present
  when: '"pam" in ansible_facts.packages'
  tags:
  - accounts_password_pam_unix_rounds_system_auth
  - configure_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed

- name: Set number of Password Hashing Rounds - system-auth - Check the proper remediation
    for the system
  block:

  - name: Set number of Password Hashing Rounds - system-auth - Define the PAM file
      to be edited as a local fact
    ansible.builtin.set_fact:
      pam_file_path: /etc/pam.d/system-auth

  - name: Set number of Password Hashing Rounds - system-auth - Check if system relies
      on authselect tool
    ansible.builtin.stat:
      path: /usr/bin/authselect
    register: result_authselect_present

  - name: Set number of Password Hashing Rounds - system-auth - Ensure authselect
      custom profile is used if authselect is present
    block:

    - name: Set number of Password Hashing Rounds - system-auth - Check integrity
        of authselect current profile
      ansible.builtin.command:
        cmd: authselect check
      register: result_authselect_check_cmd
      changed_when: false
      failed_when: false

    - name: Set number of Password Hashing Rounds - system-auth - Informative message
        based on the authselect integrity check result
      ansible.builtin.assert:
        that:
        - result_authselect_check_cmd.rc == 0
        fail_msg:
        - authselect integrity check failed. Remediation aborted!
        - This remediation could not be applied because an authselect profile was
          not selected or the selected profile is not intact.
        - It is not recommended to manually edit the PAM files when authselect tool
          is available.
        - In cases where the default authselect profile does not cover a specific
          demand, a custom authselect profile is recommended.
        success_msg:
        - authselect integrity check passed

    - name: Set number of Password Hashing Rounds - system-auth - Get authselect current
        profile
      ansible.builtin.shell:
        cmd: authselect current -r | awk '{ print $1 }'
      register: result_authselect_profile
      changed_when: false
      when:
      - result_authselect_check_cmd is success

    - name: Set number of Password Hashing Rounds - system-auth - Define the current
        authselect profile as a local fact
      ansible.builtin.set_fact:
        authselect_current_profile: '{{ result_authselect_profile.stdout }}'
        authselect_custom_profile: '{{ result_authselect_profile.stdout }}'
      when:
      - result_authselect_profile is not skipped
      - result_authselect_profile.stdout is match("custom/")

    - name: Set number of Password Hashing Rounds - system-auth - Define the new authselect
        custom profile as a local fact
      ansible.builtin.set_fact:
        authselect_current_profile: '{{ result_authselect_profile.stdout }}'
        authselect_custom_profile: custom/hardening
      when:
      - result_authselect_profile is not skipped
      - result_authselect_profile.stdout is not match("custom/")

    - name: Set number of Password Hashing Rounds - system-auth - Get authselect current
        features to also enable them in the custom profile
      ansible.builtin.shell:
        cmd: authselect current | tail -n+3 | awk '{ print $2 }'
      register: result_authselect_features
      changed_when: false
      when:
      - result_authselect_profile is not skipped
      - authselect_current_profile is not match("custom/")

    - name: Set number of Password Hashing Rounds - system-auth - Check if any custom
        profile with the same name was already created
      ansible.builtin.stat:
        path: /etc/authselect/{{ authselect_custom_profile }}
      register: result_authselect_custom_profile_present
      changed_when: false
      when:
      - authselect_current_profile is not match("custom/")

    - name: Set number of Password Hashing Rounds - system-auth - Create an authselect
        custom profile based on the current profile
      ansible.builtin.command:
        cmd: authselect create-profile hardening -b {{ authselect_current_profile
          }}
      when:
      - result_authselect_check_cmd is success
      - authselect_current_profile is not match("custom/")
      - not result_authselect_custom_profile_present.stat.exists

    - name: Set number of Password Hashing Rounds - system-auth - Ensure authselect
        changes are applied
      ansible.builtin.command:
        cmd: authselect apply-changes -b --backup=before-hardening-custom-profile
      when:
      - result_authselect_check_cmd is success
      - result_authselect_profile is not skipped
      - authselect_current_profile is not match("custom/")
      - authselect_custom_profile is not match(authselect_current_profile)

    - name: Set number of Password Hashing Rounds - system-auth - Ensure the authselect
        custom profile is selected
      ansible.builtin.command:
        cmd: authselect select {{ authselect_custom_profile }}
      register: result_pam_authselect_select_profile
      when:
      - result_authselect_check_cmd is success
      - result_authselect_profile is not skipped
      - authselect_current_profile is not match("custom/")
      - authselect_custom_profile is not match(authselect_current_profile)

    - name: Set number of Password Hashing Rounds - system-auth - Restore the authselect
        features in the custom profile
      ansible.builtin.command:
        cmd: authselect enable-feature {{ item }}
      loop: '{{ result_authselect_features.stdout_lines }}'
      register: result_pam_authselect_restore_features
      when:
      - result_authselect_profile is not skipped
      - result_authselect_features is not skipped
      - result_pam_authselect_select_profile is not skipped

    - name: Set number of Password Hashing Rounds - system-auth - Ensure authselect
        changes are applied
      ansible.builtin.command:
        cmd: authselect apply-changes -b --backup=after-hardening-custom-profile
      when:
      - result_authselect_check_cmd is success
      - result_authselect_profile is not skipped
      - result_pam_authselect_restore_features is not skipped

    - name: Set number of Password Hashing Rounds - system-auth - Change the PAM file
        to be edited according to the custom authselect profile
      ansible.builtin.set_fact:
        pam_file_path: /etc/authselect/{{ authselect_custom_profile }}/{{ pam_file_path
          | basename }}
    when:
    - result_authselect_present.stat.exists

  - name: Set number of Password Hashing Rounds - system-auth - Check if expected
      PAM module line is present in {{ pam_file_path }}
    ansible.builtin.lineinfile:
      path: '{{ pam_file_path }}'
      regexp: ^\s*password\s+{{ 'sufficient' | regex_escape() }}\s+pam_unix.so\s*.*
      state: absent
    check_mode: true
    changed_when: false
    register: result_pam_line_present

  - name: Set number of Password Hashing Rounds - system-auth - Include or update
      the PAM module line in {{ pam_file_path }}
    block:

    - name: Set number of Password Hashing Rounds - system-auth - Check if required
        PAM module line is present in {{ pam_file_path }} with different control
      ansible.builtin.lineinfile:
        path: '{{ pam_file_path }}'
        regexp: ^\s*password\s+.*\s+pam_unix.so\s*
        state: absent
      check_mode: true
      changed_when: false
      register: result_pam_line_other_control_present

    - name: Set number of Password Hashing Rounds - system-auth - Ensure the correct
        control for the required PAM module line in {{ pam_file_path }}
      ansible.builtin.replace:
        dest: '{{ pam_file_path }}'
        regexp: ^(\s*password\s+).*(\bpam_unix.so.*)
        replace: \1sufficient \2
      register: result_pam_module_edit
      when:
      - result_pam_line_other_control_present.found == 1

    - name: Set number of Password Hashing Rounds - system-auth - Ensure the required
        PAM module line is included in {{ pam_file_path }}
      ansible.builtin.lineinfile:
        dest: '{{ pam_file_path }}'
        line: password    sufficient    pam_unix.so
      register: result_pam_module_add
      when:
      - result_pam_line_other_control_present.found == 0 or result_pam_line_other_control_present.found
        > 1

    - name: Set number of Password Hashing Rounds - system-auth - Ensure authselect
        changes are applied
      ansible.builtin.command:
        cmd: authselect apply-changes -b
      when:
      - result_authselect_present is defined
      - result_authselect_present.stat.exists
      - |-
        (result_pam_module_add is defined and result_pam_module_add.changed)
         or (result_pam_module_edit is defined and result_pam_module_edit.changed)
    when:
    - result_pam_line_present.found is defined
    - result_pam_line_present.found == 0

  - name: Set number of Password Hashing Rounds - system-auth - Check if the required
      PAM module option is present in {{ pam_file_path }}
    ansible.builtin.lineinfile:
      path: '{{ pam_file_path }}'
      regexp: ^\s*password\s+{{ 'sufficient' | regex_escape() }}\s+pam_unix.so\s*.*\srounds\b
      state: absent
    check_mode: true
    changed_when: false
    register: result_pam_module_rounds_option_present

  - name: Set number of Password Hashing Rounds - system-auth - Ensure the "rounds"
      PAM option for "pam_unix.so" is included in {{ pam_file_path }}
    ansible.builtin.lineinfile:
      path: '{{ pam_file_path }}'
      backrefs: true
      regexp: ^(\s*password\s+{{ 'sufficient' | regex_escape() }}\s+pam_unix.so.*)
      line: \1 rounds={{ var_password_pam_unix_rounds }}
      state: present
    register: result_pam_rounds_add
    when:
    - result_pam_module_rounds_option_present.found == 0

  - name: Set number of Password Hashing Rounds - system-auth - Ensure the required
      value for "rounds" PAM option from "pam_unix.so" in {{ pam_file_path }}
    ansible.builtin.lineinfile:
      path: '{{ pam_file_path }}'
      backrefs: true
      regexp: ^(\s*password\s+{{ 'sufficient' | regex_escape() }}\s+pam_unix.so\s+.*)(rounds)=[0-9a-zA-Z]+\s*(.*)
      line: \1\2={{ var_password_pam_unix_rounds }} \3
    register: result_pam_rounds_edit
    when:
    - result_pam_module_rounds_option_present.found > 0

  - name: Set number of Password Hashing Rounds - system-auth - Ensure authselect
      changes are applied
    ansible.builtin.command:
      cmd: authselect apply-changes -b
    when:
    - result_authselect_present.stat.exists
    - |-
      (result_pam_rounds_add is defined and result_pam_rounds_add.changed)
       or (result_pam_rounds_edit is defined and result_pam_rounds_edit.changed)
  when:
  - '"pam" in ansible_facts.packages'
  - result_pam_file_present.stat.exists
  tags:
  - accounts_password_pam_unix_rounds_system_auth
  - configure_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed

# Remediation is applicable only in certain platforms
if rpm --quiet -q pam; then
var_password_pam_unix_rounds='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_var_password_pam_unix_rounds" use="legacy"/>'


if [ -e "/etc/pam.d/system-auth" ] ; then    PAM_FILE_PATH="/etc/pam.d/system-auth"
    if [ -f /usr/bin/authselect ]; then
        
        if ! authselect check; then
        echo "
        authselect integrity check failed. Remediation aborted!
        This remediation could not be applied because an authselect profile was not selected or the selected profile is not intact.
        It is not recommended to manually edit the PAM files when authselect tool is available.
        In cases where the default authselect profile does not cover a specific demand, a custom authselect profile is recommended."
        exit 1
        fi

        CURRENT_PROFILE=$(authselect current -r | awk '{ print $1 }')
        # If not already in use, a custom profile is created preserving the enabled features.
        if [[ ! $CURRENT_PROFILE == custom/* ]]; then
            ENABLED_FEATURES=$(authselect current | tail -n+3 | awk '{ print $2 }')
            authselect create-profile hardening -b $CURRENT_PROFILE
            CURRENT_PROFILE="custom/hardening"
            
            authselect apply-changes -b --backup=before-hardening-custom-profile
            authselect select $CURRENT_PROFILE
            for feature in $ENABLED_FEATURES; do
                authselect enable-feature $feature;
            done
            
            authselect apply-changes -b --backup=after-hardening-custom-profile
        fi
        PAM_FILE_NAME=$(basename "/etc/pam.d/system-auth")
        PAM_FILE_PATH="/etc/authselect/$CURRENT_PROFILE/$PAM_FILE_NAME"

        authselect apply-changes -b
    fi
    if ! grep -qP '^\s*password\s+'"sufficient"'\s+pam_unix.so\s*.*' "$PAM_FILE_PATH"; then
            # Line matching group + control + module was not found. Check group + module.
            if [ "$(grep -cP '^\s*password\s+.*\s+pam_unix.so\s*' "$PAM_FILE_PATH")" -eq 1 ]; then
                # The control is updated only if one single line matches.
                sed -i -E --follow-symlinks 's/^(\s*password\s+).*(\bpam_unix.so.*)/\1'"sufficient"' \2/' "$PAM_FILE_PATH"
            else
                echo 'password    '"sufficient"'    pam_unix.so' >> "$PAM_FILE_PATH"
            fi
        fi
        # Check the option
        if ! grep -qP '^\s*password\s+'"sufficient"'\s+pam_unix.so\s*.*\srounds\b' "$PAM_FILE_PATH"; then
            sed -i -E --follow-symlinks '/\s*password\s+'"sufficient"'\s+pam_unix.so.*/ s/$/ rounds='"$var_password_pam_unix_rounds"'/' "$PAM_FILE_PATH"
        else
            sed -i -E --follow-symlinks 's/(\s*password\s+'"sufficient"'\s+pam_unix.so\s+.*)('"rounds"'=)[[:alnum:]]+\s*(.*)/\1\2'"$var_password_pam_unix_rounds"' \3/' "$PAM_FILE_PATH"
        fi
    if [ -f /usr/bin/authselect ]; then
        
        authselect apply-changes -b
    fi
else
    echo "/etc/pam.d/system-auth was not found" >&2
fi

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

Set number of Password Hashing Rounds - system-auth

Description

Rationale

Remediation Templates

An Ansible Snippet

A Shell Script