Enable Kernel Parameter to Ignore ICMP Broadcast Echo Requests on IPv4 Interfaces

An XCCDF Rule

Description

To set the runtime status of the net.ipv4.icmp_echo_ignore_broadcasts kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1

To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:

net.ipv4.icmp_echo_ignore_broadcasts = 1

Rationale

Responding to broadcast (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks.
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

ID: xccdf_org.ssgproject.content_rule_sysctl_net_ipv4_icmp_echo_ignore_broadcasts
Severity: Medium
References: 1 11 12 13 14 15 16 18 2 3 4 6 7 8 9

5.10.1.1

APO01.06 APO13.01 BAI04.04 BAI10.01 BAI10.02 BAI10.03 BAI10.05 DSS01.03 DSS01.05 DSS03.01 DSS03.05 DSS05.02 DSS05.04 DSS05.05 DSS05.07 DSS06.02 DSS06.06

3.1.20

CCI-000366

4.2.3.4 4.3.3.4 4.3.3.5.1 4.3.3.5.2 4.3.3.5.3 4.3.3.5.4 4.3.3.5.5 4.3.3.5.6 4.3.3.5.7 4.3.3.5.8 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 4.3.3.7.1 4.3.3.7.2 4.3.3.7.3 4.3.3.7.4 4.3.4.3.2 4.3.4.3.3 4.4.3.3

SR 1.1 SR 1.10 SR 1.11 SR 1.12 SR 1.13 SR 1.2 SR 1.3 SR 1.4 SR 1.5 SR 1.6 SR 1.7 SR 1.8 SR 1.9 SR 2.1 SR 2.2 SR 2.3 SR 2.4 SR 2.5 SR 2.6 SR 2.7 SR 3.1 SR 3.5 SR 3.8 SR 4.1 SR 4.3 SR 5.1 SR 5.2 SR 5.3 SR 6.2 SR 7.1 SR 7.2 SR 7.6

A.10.1.1 A.11.1.4 A.11.1.5 A.11.2.1 A.12.1.1 A.12.1.2 A.12.1.3 A.12.5.1 A.12.6.2 A.13.1.1 A.13.1.2 A.13.1.3 A.13.2.1 A.13.2.2 A.13.2.3 A.13.2.4 A.14.1.2 A.14.1.3 A.14.2.2 A.14.2.3 A.14.2.4 A.17.2.1 A.6.1.2 A.7.1.1 A.7.1.2 A.7.3.1 A.8.2.2 A.8.2.3 A.9.1.1 A.9.1.2 A.9.2.3 A.9.4.1 A.9.4.4 A.9.4.5

CIP-007-3 R4 CIP-007-3 R4.1 CIP-007-3 R4.2 CIP-007-3 R5.1

CM-7(a) CM-7(b) SC-5

DE.AE-1 DE.CM-1 ID.AM-3 PR.AC-5 PR.DS-4 PR.DS-5 PR.IP-1 PR.PT-3 PR.PT-4

Req-1.4.3

SRG-OS-000480-GPOS-00227

OL07-00-040630

SV-221877r880648_rule

1.4.2
Updated: about 1 year ago

# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then

# Comment out any occurrences of net.ipv4.icmp_echo_ignore_broadcasts from /etc/sysctl.d/*.conf files

for f in /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf; do
  matching_list=$(grep -P '^(?!#).*[\s]*net.ipv4.icmp_echo_ignore_broadcasts.*$' $f | uniq )
  if ! test -z "$matching_list"; then
    while IFS= read -r entry; do
      escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
      # comment out "net.ipv4.icmp_echo_ignore_broadcasts" matches to preserve user data
      sed -i "s/^${escaped_entry}$/# &/g" $f
    done <<< "$matching_list"
  fi
done

#
# Set sysctl config file which to save the desired value
#

SYSCONFIG_FILE="/etc/sysctl.conf"

sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value" use="legacy"/>'


#
# Set runtime for net.ipv4.icmp_echo_ignore_broadcasts
#
/sbin/sysctl -q -n -w net.ipv4.icmp_echo_ignore_broadcasts="$sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value"

#
# If net.ipv4.icmp_echo_ignore_broadcasts present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.icmp_echo_ignore_broadcasts = value" to /etc/sysctl.conf
#

# Strip any search characters in the key arg so that the key can be replaced without
# adding any search characters to the config file.
stripped_key=$(sed 's/[\^=\$,;+]*//g' <<< "^net.ipv4.icmp_echo_ignore_broadcasts")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "$sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value"

# If the key exists, change it. Otherwise, add it to the config_file.
# We search for the key string followed by a word boundary (matched by \>),
# so if we search for 'setting', 'setting2' won't match.
if LC_ALL=C grep -q -m 1 -i -e "^net.ipv4.icmp_echo_ignore_broadcasts\\>" "${SYSCONFIG_FILE}"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^net.ipv4.icmp_echo_ignore_broadcasts\\>.*/$escaped_formatted_output/gi" "${SYSCONFIG_FILE}"
else
    if [[ -s "${SYSCONFIG_FILE}" ]] && [[ -n "$(tail -c 1 -- "${SYSCONFIG_FILE}" || true)" ]]; then
        LC_ALL=C sed -i --follow-symlinks '$a'\\ "${SYSCONFIG_FILE}"
    fi
    printf '%s\n' "$formatted_output" >> "${SYSCONFIG_FILE}"
fi

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

- name: List /etc/sysctl.d/*.conf files
  find:
    paths:
    - /etc/sysctl.d/
    - /run/sysctl.d/
    - /usr/local/lib/sysctl.d/    contains: ^[\s]*net.ipv4.icmp_echo_ignore_broadcasts.*$
    patterns: '*.conf'
    file_type: any
  register: find_sysctl_d
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CJIS-5.10.1.1
  - DISA-STIG-OL07-00-040630
  - NIST-800-171-3.1.20
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - PCI-DSS-Req-1.4.3
  - PCI-DSSv4-1.4.2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_icmp_echo_ignore_broadcasts

- name: Comment out any occurrences of net.ipv4.icmp_echo_ignore_broadcasts from config
    files
  replace:
    path: '{{ item.path }}'
    regexp: ^[\s]*net.ipv4.icmp_echo_ignore_broadcasts
    replace: '#net.ipv4.icmp_echo_ignore_broadcasts'
  loop: '{{ find_sysctl_d.files }}'
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CJIS-5.10.1.1
  - DISA-STIG-OL07-00-040630
  - NIST-800-171-3.1.20
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - PCI-DSS-Req-1.4.3
  - PCI-DSSv4-1.4.2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_icmp_echo_ignore_broadcasts
- name: XCCDF Value sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value # promote to variable
  set_fact:
    sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value: !!str <xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value" use="legacy"/>
  tags:
    - always

- name: Ensure sysctl net.ipv4.icmp_echo_ignore_broadcasts is set
  sysctl:
    name: net.ipv4.icmp_echo_ignore_broadcasts
    value: '{{ sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value }}'
    sysctl_file: /etc/sysctl.conf
    state: present
    reload: true
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CJIS-5.10.1.1
  - DISA-STIG-OL07-00-040630
  - NIST-800-171-3.1.20
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - PCI-DSS-Req-1.4.3
  - PCI-DSSv4-1.4.2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_icmp_echo_ignore_broadcasts

Enable Kernel Parameter to Ignore ICMP Broadcast Echo Requests on IPv4 Interfaces

Description

Rationale

Remediation - Shell Script

Remediation - Ansible