Set the GNOME3 Login Number of Failures

An XCCDF Rule

Description

In the default graphical environment, the GNOME3 login screen and be configured to restart the authentication process after a configured number of attempts. This can be configured by setting allowed-failures to 3 or less.

To enable, add or edit allowed-failures to /etc/dconf/db/gdm.d/00-security-settings. For example:

[org/gnome/login-screen]
allowed-failures=3

Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example:

/org/gnome/login-screen/allowed-failures

After the settings have been set, run dconf update.

Rationale

Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks.

ID: xccdf_org.ssgproject.content_rule_dconf_gnome_login_retries
Severity: Medium
References: 3.1.8

FMT_MOF_EXT.1

CCE-80771-9
Updated: about 1 year ago

# Remediation is applicable only in certain platforms
if rpm --quiet -q gdm && { [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; }; then

# Check for setting in any of the DConf db directories
# If files contain ibus or distro, ignore them.
# The assignment assumes that individual filenames don't contain :readarray -t SETTINGSFILES < <(grep -r "\\[org/gnome/login-screen\\]" "/etc/dconf/db/" \
                                | grep -v 'distro\|ibus\|gdm.d' | cut -d":" -f1)
DCONFFILE="/etc/dconf/db/gdm.d/00-security-settings"
DBDIR="/etc/dconf/db/gdm.d"

mkdir -p "${DBDIR}"

# Comment out the configurations in databases different from the target one
if [ "${#SETTINGSFILES[@]}" -ne 0 ]
then
    if grep -q "^\\s*allowed-failures\\s*=" "${SETTINGSFILES[@]}"
    then
        
        sed -Ei "s/(^\s*)allowed-failures(\s*=)/#\1allowed-failures\2/g" "${SETTINGSFILES[@]}"
    fi
fi

[ ! -z "${DCONFFILE}" ] && echo "" >> "${DCONFFILE}"
if ! grep -q "\\[org/gnome/login-screen\\]" "${DCONFFILE}"
then
    printf '%s\n' "[org/gnome/login-screen]" >> ${DCONFFILE}
fi

escaped_value="$(sed -e 's/\\/\\\\/g' <<< "3")"
if grep -q "^\\s*allowed-failures\\s*=" "${DCONFFILE}"
then
        sed -i "s/\\s*allowed-failures\\s*=\\s*.*/allowed-failures=${escaped_value}/g" "${DCONFFILE}"
    else
        sed -i "\\|\\[org/gnome/login-screen\\]|a\\allowed-failures=${escaped_value}" "${DCONFFILE}"
fi

dconf update
# Check for setting in any of the DConf db directories
LOCKFILES=$(grep -r "^/org/gnome/login-screen/allowed-failures$" "/etc/dconf/db/" \
            | grep -v 'distro\|ibus\|gdm.d' | grep ":" | cut -d":" -f1)
LOCKSFOLDER="/etc/dconf/db/gdm.d/locks"

mkdir -p "${LOCKSFOLDER}"

# Comment out the configurations in databases different from the target one
if [[ ! -z "${LOCKFILES}" ]]
then
    sed -i -E "s|^/org/gnome/login-screen/allowed-failures$|#&|" "${LOCKFILES[@]}"
fi

if ! grep -qr "^/org/gnome/login-screen/allowed-failures$" /etc/dconf/db/gdm.d/
then
    echo "/org/gnome/login-screen/allowed-failures" >> "/etc/dconf/db/gdm.d/locks/00-security-settings-lock"
fi

dconf update

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

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CCE-80771-9
  - NIST-800-171-3.1.8  - dconf_gnome_login_retries
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

- name: Enable the GNOME3 Login Number of Failures
  ini_file:
    dest: /etc/dconf/db/gdm.d/00-security-settings
    section: org/gnome/login-screen
    option: allowed-failures
    value: '3'
    create: true
    no_extra_spaces: true
  when:
  - '"gdm" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-80771-9
  - NIST-800-171-3.1.8
  - dconf_gnome_login_retries
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

- name: Prevent user modification of GNOME3 Login Number of Failures
  lineinfile:
    path: /etc/dconf/db/gdm.d/locks/00-security-settings-lock
    regexp: ^/org/gnome/login-screen/allowed-failures$
    line: /org/gnome/login-screen/allowed-failures
    create: true
  when:
  - '"gdm" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-80771-9
  - NIST-800-171-3.1.8
  - dconf_gnome_login_retries
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

- name: Dconf Update
  command: dconf update
  when:
  - '"gdm" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-80771-9
  - NIST-800-171-3.1.8
  - dconf_gnome_login_retries
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

Set the GNOME3 Login Number of Failures

Description

Rationale

Remediation - Shell Script

Remediation - Ansible