Implement Blank Screensaver

An XCCDF Rule

Description

To set the screensaver mode in the GNOME3 desktop to a blank screen, add or set picture-uri to string '' in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/screensaver]
picture-uri=string ''

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

/org/gnome/desktop/screensaver/picture-uri

After the settings have been set, run dconf update.

Rationale

Setting the screensaver mode to blank-only conceals the contents of the display from passersby.

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

5.5.5

DSS05.04 DSS05.10 DSS06.10

3.1.10

CCI-000060

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

SR 1.1 SR 1.10 SR 1.2 SR 1.5 SR 1.7 SR 1.8 SR 1.9

A.18.1.4 A.9.2.1 A.9.2.4 A.9.3.1 A.9.4.2 A.9.4.3

AC-11(1) AC-11(1).1 CM-6(a)

PR.AC-7

Req-8.1.8

8.2 8.2.8

SRG-OS-000031-GPOS-00012
Updated: over 1 year ago

Remediation Templates

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CJIS-5.5.5
  - NIST-800-171-3.1.10  - NIST-800-53-AC-11(1)
  - NIST-800-53-AC-11(1).1
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-8.1.8
  - PCI-DSSv4-8.2
  - PCI-DSSv4-8.2.8
  - dconf_gnome_screensaver_mode_blank
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy
- name: Implement Blank Screensaver
  ini_file:
    dest: /etc/dconf/db/local.d/00-security-settings
    section: org/gnome/desktop/screensaver
    option: picture-uri
    value: string ''
    create: true
    no_extra_spaces: true
  when:
  - '"gdm" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CJIS-5.5.5
  - NIST-800-171-3.1.10
  - NIST-800-53-AC-11(1)
  - NIST-800-53-AC-11(1).1
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-8.1.8
  - PCI-DSSv4-8.2
  - PCI-DSSv4-8.2.8
  - dconf_gnome_screensaver_mode_blank
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

- name: Prevent user modification of GNOME picture-uri
  lineinfile:
    path: /etc/dconf/db/local.d/locks/00-security-settings-lock
    regexp: ^/org/gnome/desktop/screensaver/picture-uri$
    line: /org/gnome/desktop/screensaver/picture-uri
    create: true
  when:
  - '"gdm" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CJIS-5.5.5
  - NIST-800-171-3.1.10
  - NIST-800-53-AC-11(1)
  - NIST-800-53-AC-11(1).1
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-8.1.8
  - PCI-DSSv4-8.2
  - PCI-DSSv4-8.2.8
  - dconf_gnome_screensaver_mode_blank
  - 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:
  - CJIS-5.5.5
  - NIST-800-171-3.1.10
  - NIST-800-53-AC-11(1)
  - NIST-800-53-AC-11(1).1
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-8.1.8
  - PCI-DSSv4-8.2
  - PCI-DSSv4-8.2.8
  - dconf_gnome_screensaver_mode_blank
  - low_complexity
  - medium_disruption
  - medium_severity
  - no_reboot_needed
  - unknown_strategy

# 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/desktop/screensaver\\]" "/etc/dconf/db/" \                                | grep -v 'distro\|ibus\|local.d' | cut -d":" -f1)
DCONFFILE="/etc/dconf/db/local.d/00-security-settings"
DBDIR="/etc/dconf/db/local.d"

mkdir -p "${DBDIR}"

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

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

escaped_value="$(sed -e 's/\\/\\\\/g' <<< "string ''")"
if grep -q "^\\s*picture-uri\\s*=" "${DCONFFILE}"
then
        sed -i "s/\\s*picture-uri\\s*=\\s*.*/picture-uri=${escaped_value}/g" "${DCONFFILE}"
    else
        sed -i "\\|\\[org/gnome/desktop/screensaver\\]|a\\picture-uri=${escaped_value}" "${DCONFFILE}"
fi
dconf update
# Check for setting in any of the DConf db directories
LOCKFILES=$(grep -r "^/org/gnome/desktop/screensaver/picture-uri$" "/etc/dconf/db/" \
            | grep -v 'distro\|ibus\|local.d' | grep ":" | cut -d":" -f1)
LOCKSFOLDER="/etc/dconf/db/local.d/locks"

mkdir -p "${LOCKSFOLDER}"

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

if ! grep -qr "^/org/gnome/desktop/screensaver/picture-uri$" /etc/dconf/db/local.d/
then
    echo "/org/gnome/desktop/screensaver/picture-uri" >> "/etc/dconf/db/local.d/locks/00-security-settings-lock"
fi
dconf update

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

Implement Blank Screensaver

Description

Rationale

Remediation Templates

An Ansible Snippet

A Shell Script