Set PAM's Common Authentication Hashing Algorithm

An XCCDF Rule

Description

The PAM system service can be configured to only store encrypted representations of passwords. In /etc/pam.d/common-auth, the auth section of the file controls which PAM modules execute during a password change. Set the pam_unix.so module in the auth section to include the argument sha512, as shown below:

auth   required    pam_unix.so sha512 other arguments...

This will help ensure when local users change their authentication method, hashes for the new authentications will be generated using the SHA-512 algorithm. This is the default.

Rationale

Unapproved mechanisms used for authentication to the cryptographic module are not verified and therefore cannot be relied on to provide confidentiality or integrity, and data may be compromised. This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.

ID: xccdf_org.ssgproject.content_rule_set_password_hashing_algorithm_commonauth
Severity: Medium
References: CCI-000803

IA-7 IA-7.1

Req-8.2.1

8.3.2

SRG-OS-000120-GPOS-00061

CCE-91647-8
Updated: about 1 year ago

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Set control_flag fact
  set_fact:
    control_flag: required
  when: '"pam" in ansible_facts.packages'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Check to see if 'pam_unix.so' module is configured in '/etc/pam.d/common-auth'
  shell: |
    set -o pipefail
    grep -E '^\s*auth\s+\S+\s+pam_unix.so' /etc/pam.d/common-auth || true
  register: check_pam_module_result
  when: '"pam" in ansible_facts.packages'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Configure 'pam_unix.so' module in '/etc/pam.d/common-auth'
  lineinfile:
    path: /etc/pam.d/common-auth
    line: auth required pam_unix.so
    state: present
  when:
  - '"pam" in ansible_facts.packages'
  - '"pam_unix.so" not in check_pam_module_result.stdout'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Ensure 'pam_unix.so' module has conforming control flag
  lineinfile:
    path: /etc/pam.d/common-auth
    regexp: ^(\s*auth\s+)\S+(\s+pam_unix.so\s+.*)
    line: \g<1>required\g<2>
    backrefs: true
  when:
  - '"pam" in ansible_facts.packages'
  - control_flag|length
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Set argument_value fact
  set_fact:
    argument_value: ''
  when: '"pam" in ansible_facts.packages'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Ensure "pam_unix.so" module has argument "sha512"
  lineinfile:
    path: /etc/pam.d/common-auth
    regexp: ^(\s*auth\s+required\s+pam_unix.so(?:\s+\S+)*\s+sha512=)(?!)\S*((\s+\S+)*\s*\\*\s*)$
    line: \g<1>\g<2>
    backrefs: true
  when:
  - '"pam" in ansible_facts.packages'
  - argument_value|length
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Check the presence of "sha512" argument in "pam_unix.so" module
  shell: |
    set -o pipefail
    grep -E '^\s*auth\s+required\s+pam_unix.so.*\s+sha512(=|\s|\s*$)' /etc/pam.d/common-auth || true
  register: check_pam_module_argument_result
  when: '"pam" in ansible_facts.packages'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

- name: Add "sha512" argument to "pam_unix.so" module
  lineinfile:
    path: /etc/pam.d/common-auth
    regexp: ^(\s*auth\s+required\s+pam_unix.so)((\s+\S+)*\s*(\\)*$)
    line: \g<1> sha512\g<2>
    backrefs: true
  when:
  - '"pam" in ansible_facts.packages'
  - '"sha512" not in check_pam_module_argument_result.stdout'
  tags:
  - CCE-91647-8
  - NIST-800-53-IA-7
  - NIST-800-53-IA-7.1
  - PCI-DSS-Req-8.2.1
  - PCI-DSSv4-8.3.2
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - set_password_hashing_algorithm_commonauth

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

if [ -e "/etc/pam.d/common-auth" ] ; then
    valueRegex="" defaultValue=""
    # 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 'type' if it's wrong
    if grep -q -P "^\\s*(?"'!'"auth\\s)[[:alnum:]]+\\s+[[:alnum:]]+\\s+pam_unix.so" < "/etc/pam.d/common-auth" ; then
        sed --follow-symlinks -i -E -e "s/^(\\s*)[[:alnum:]]+(\\s+[[:alnum:]]+\\s+pam_unix.so)/\\1auth\\2/" "/etc/pam.d/common-auth"
    fi

    # fix 'control' if it's wrong
    if grep -q -P "^\\s*auth\\s+(?"'!'"required)[[:alnum:]]+\\s+pam_unix.so" < "/etc/pam.d/common-auth" ; then
        sed --follow-symlinks -i -E -e "s/^(\\s*auth\\s+)[[:alnum:]]+(\\s+pam_unix.so)/\\1required\\2/" "/etc/pam.d/common-auth"
    fi

    # fix the value for 'option' if one exists but does not match 'valueRegex'
    if grep -q -P "^\\s*auth\\s+required\\s+pam_unix.so(\\s.+)?\\s+sha512(?"'!'"${valueRegex}(\\s|\$))" < "/etc/pam.d/common-auth" ; then
        sed --follow-symlinks -i -E -e "s/^(\\s*auth\\s+required\\s+pam_unix.so(\\s.+)?\\s)sha512=[^[:space:]]*/\\1sha512${defaultValue}/" "/etc/pam.d/common-auth"

    # add 'option=default' if option is not set
    elif grep -q -E "^\\s*auth\\s+required\\s+pam_unix.so" < "/etc/pam.d/common-auth" &&
            grep    -E "^\\s*auth\\s+required\\s+pam_unix.so" < "/etc/pam.d/common-auth" | grep -q -E -v "\\ssha512(=|\\s|\$)" ; then

        sed --follow-symlinks -i -E -e "s/^(\\s*auth\\s+required\\s+pam_unix.so[^\\n]*)/\\1 sha512${defaultValue}/" "/etc/pam.d/common-auth"
    # add a new entry if none exists
    elif ! grep -q -P "^\\s*auth\\s+required\\s+pam_unix.so(\\s.+)?\\s+sha512${valueRegex}(\\s|\$)" < "/etc/pam.d/common-auth" ; then
        echo "auth required pam_unix.so sha512${defaultValue}" >> "/etc/pam.d/common-auth"
    fi
else
    echo "/etc/pam.d/common-auth doesn't exist" >&2
fi

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

Set PAM's Common Authentication Hashing Algorithm

Description

Rationale

Remediation - Ansible

Remediation - Shell Script