Do Not Show System Messages When Unsuccessful Logon Attempts Occur

An XCCDF Rule

Description

This rule ensures the system prevents informative messages from being presented to the user pertaining to logon information after a number of incorrect login attempts using pam_faillock.so. pam_faillock.so module requires multiple entries in pam files. These entries must be carefully defined to work as expected. In order to avoid errors when manually editing these files, it is recommended to use the appropriate tools, such as authselect or authconfig, depending on the OS version.

warning alert: Warning

If the system relies on authselect tool to manage PAM settings, the remediation will also use authselect tool. However, if any manual modification was made in PAM files, the authselect integrity check will fail and the remediation will be aborted in order to preserve intentional changes. In this case, an informative message will be shown in the remediation report. If the system supports the /etc/security/faillock.conf file, the pam_faillock parameters should be defined in faillock.conf file.

Rationale

The pam_faillock module without the silent option will leak information about the existence or non-existence of a user account in the system because the failures are not recorded for unknown users. The message about the user account being locked is never displayed for non-existing user accounts allowing the adversary to infer that a particular account exists or not on the system.

ID: xccdf_org.ssgproject.content_rule_accounts_passwords_pam_faillock_silent
Severity: Medium
References: CCI-000044 CCI-002238

SRG-OS-000021-GPOS-00005 SRG-OS-000329-GPOS-00128

UBTU-20-010072

SV-238235r853414_rule
Updated: 8 months ago

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Check
    if system relies on authselect tool
  ansible.builtin.stat:
    path: /usr/bin/authselect
  register: result_authselect_present
  when: '"libpam-runtime" in ansible_facts.packages'
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Remediation
    where authselect tool is present
  block:

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Check
      integrity of authselect current profile
    ansible.builtin.command:
      cmd: authselect check
    register: result_authselect_check_cmd
    changed_when: false
    failed_when: false

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - 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: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Get
      authselect current features
    ansible.builtin.shell:
      cmd: authselect current | tail -n+3 | awk '{ print $2 }'
    register: result_authselect_features
    changed_when: false
    when:
    - result_authselect_check_cmd is success

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Ensure
      "with-faillock" feature is enabled using authselect tool
    ansible.builtin.command:
      cmd: authselect enable-feature with-faillock
    register: result_authselect_enable_feature_cmd
    when:
    - result_authselect_check_cmd is success
    - result_authselect_features.stdout is not search("with-faillock")

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Ensure
      authselect changes are applied
    ansible.builtin.command:
      cmd: authselect apply-changes -b
    when:
    - result_authselect_enable_feature_cmd is not skipped
    - result_authselect_enable_feature_cmd is success
  when:
  - '"libpam-runtime" in ansible_facts.packages'
  - result_authselect_present.stat.exists
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Remediation
    where authselect tool is not present
  block:

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Check
      if pam_faillock.so is already enabled
    ansible.builtin.lineinfile:
      path: /etc/pam.d/system-auth
      regexp: .*auth.*pam_faillock\.so (preauth|authfail)
      state: absent
    check_mode: true
    changed_when: false
    register: result_pam_faillock_is_enabled

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Enable
      pam_faillock.so preauth editing PAM files
    ansible.builtin.lineinfile:
      path: '{{ item }}'
      line: auth        required      pam_faillock.so preauth
      insertbefore: ^auth.*sufficient.*pam_unix\.so.*
      state: present
    loop:
    - /etc/pam.d/system-auth
    - /etc/pam.d/password-auth
    when:
    - result_pam_faillock_is_enabled.found == 0

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Enable
      pam_faillock.so authfail editing PAM files
    ansible.builtin.lineinfile:
      path: '{{ item }}'
      line: auth        required      pam_faillock.so authfail
      insertbefore: ^auth.*required.*pam_deny\.so.*
      state: present
    loop:
    - /etc/pam.d/system-auth
    - /etc/pam.d/password-auth
    when:
    - result_pam_faillock_is_enabled.found == 0

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Enable
      pam_faillock.so account section editing PAM files
    ansible.builtin.lineinfile:
      path: '{{ item }}'
      line: account     required      pam_faillock.so
      insertbefore: ^account.*required.*pam_unix\.so.*
      state: present
    loop:
    - /etc/pam.d/system-auth
    - /etc/pam.d/password-auth
    when:
    - result_pam_faillock_is_enabled.found == 0
  when:
  - '"libpam-runtime" in ansible_facts.packages'
  - not result_authselect_present.stat.exists
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Check
    the presence of /etc/security/faillock.conf file
  ansible.builtin.stat:
    path: /etc/security/faillock.conf
  register: result_faillock_conf_check
  when: '"libpam-runtime" in ansible_facts.packages'
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Ensure
    the pam_faillock.so silent parameter in /etc/security/faillock.conf
  ansible.builtin.lineinfile:
    path: /etc/security/faillock.conf
    regexp: ^\s*silent
    line: silent
    state: present
  when:
  - '"libpam-runtime" in ansible_facts.packages'
  - result_faillock_conf_check.stat.exists
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

- name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Ensure
    the pam_faillock.so silent parameter in PAM files
  block:

  - name: Do Not Show System Messages When Unsuccessful Logon Attempts Occur - Ensure
      the inclusion of pam_faillock.so preauth silent parameter in auth section
    ansible.builtin.lineinfile:
      path: '{{ item }}'
      backrefs: true
      regexp: (^\s*auth\s+)([\w\[].*\b)(\s+pam_faillock.so preauth(:?(?!silent).)*)
      line: \1required\3 silent
      state: present
    loop:
    - /etc/pam.d/system-auth
    - /etc/pam.d/password-auth
  when:
  - '"libpam-runtime" in ansible_facts.packages'
  - not result_faillock_conf_check.stat.exists
  tags:
  - DISA-STIG-UBTU-20-010072
  - accounts_passwords_pam_faillock_silent
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy

# Remediation is applicable only in certain platforms
if dpkg-query --show --showformat='${db:Status-Status}\n' 'libpam-runtime' 2>/dev/null | grep -q installed; then

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
authselect enable-feature with-faillock

authselect apply-changes -b
else
    
pam_file="/etc/pam.d/common-auth"
if ! grep -qE '^\s*auth\s+required\s+pam_faillock\.so\s+preauth.*$' "$pam_file" ; then
    sed -i --follow-symlinks '/^auth.*pam_unix\.so.*/i auth        required      pam_faillock.so preauth' "$pam_file"
fi
if ! grep -qE '^\s*auth\s+\[default=die\]\s+pam_faillock\.so\s+authfail.*$' "$pam_file" ; then
    num_lines=$(sed -n 's/^auth.*success=\([0-9]\).*pam_unix\.so.*/\1/p' "$pam_file")
    if [ ! -z "$num_lines" ]; then
        echo "$num_lines"
        pattern=""
        for ((i=1; i <= num_lines; i++)); do
            pattern="${pattern}n;"
        done;
        sed -i --follow-symlinks '/^auth.*pam_unix\.so.*/{'$pattern'a auth        [default=die]      pam_faillock.so authfail
 }' "$pam_file"
    else
        sed -i --follow-symlinks '/^auth.*pam_unix\.so.*/a auth        [default=die]      pam_faillock.so authfail' "$pam_file"
    fi
fi
if ! grep -qE '^\s*auth\s+sufficient\s+pam_faillock\.so\s+authsucc.*$' "$pam_file" ; then
    sed -i --follow-symlinks '/^auth.*pam_faillock\.so.*authfail.*/a auth        sufficient      pam_faillock.so authsucc' "$pam_file"
fi

pam_file="/etc/pam.d/common-account"
if ! grep -qE '^\s*account\s+required\s+pam_faillock\.so.*$' "$pam_file" ; then
    echo 'account   required     pam_faillock.so' >> "$pam_file"
fi

fi



AUTH_FILES=("/etc/pam.d/common-auth" "/etc/pam.d/password-auth")

FAILLOCK_CONF="/etc/security/faillock.conf"
if [ -f $FAILLOCK_CONF ]; then
    regex="^\s*silent"
    line="silent"
    if ! grep -q $regex $FAILLOCK_CONF; then
        echo $line >> $FAILLOCK_CONF
    fi
    for pam_file in "${AUTH_FILES[@]}"
    do
        if [ -e "$pam_file" ] ; then
            PAM_FILE_PATH="$pam_file"
            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=$(basename "$pam_file")
                PAM_FILE_PATH="/etc/authselect/$CURRENT_PROFILE/$PAM_FILE_NAME"

                authselect apply-changes -b
            fi
            
        if grep -qP '^\s*auth\s.*\bpam_faillock.so\s.*\bsilent\b' "$PAM_FILE_PATH"; then
            sed -i -E --follow-symlinks 's/(.*auth.*pam_faillock.so.*)\bsilent\b=?[[:alnum:]]*(.*)/\1\2/g' "$PAM_FILE_PATH"
        fi
            if [ -f /usr/bin/authselect ]; then
                
                authselect apply-changes -b
            fi
        else
            echo "$pam_file was not found" >&2
        fi
    done
else
    for pam_file in "${AUTH_FILES[@]}"
    do
        if ! grep -qE '^\s*auth.*pam_faillock\.so (preauth|authfail).*silent' "$pam_file"; then
            sed -i --follow-symlinks '/^auth.*required.*pam_faillock\.so.*preauth.*silent.*/ s/$/ silent/' "$pam_file"
        fi
    done
fi

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

Do Not Show System Messages When Unsuccessful Logon Attempts Occur

Description

Rationale

Remediation - Ansible

Remediation - Shell Script