Set Kernel Parameter to Increase Local Port Range

An XCCDF Rule

Description

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

$ sudo sysctl -w net.ipv4.ip_local_port_range=32768 65535

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

net.ipv4.ip_local_port_range = 32768 65535

Rationale

This setting defines the local port range that is used by TCP and UDP to choose the local port. The first number is the first, the second the last local port number.

ID: xccdf_org.ssgproject.content_rule_sysctl_net_ipv4_ip_local_port_range
Severity: Medium
References: BP28(R22)

CCE-84276-5
Updated: about 1 year ago

- name: List /etc/sysctl.d/*.conf files
  find:
    paths:
    - /etc/sysctl.d/
    - /run/sysctl.d/
    - /usr/local/lib/sysctl.d/    contains: ^[\s]*net.ipv4.ip_local_port_range.*$
    patterns: '*.conf'
    file_type: any
  register: find_sysctl_d
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-84276-5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_ip_local_port_range

- name: Comment out any occurrences of net.ipv4.ip_local_port_range from config files
  replace:
    path: '{{ item.path }}'
    regexp: ^[\s]*net.ipv4.ip_local_port_range
    replace: '#net.ipv4.ip_local_port_range'
  loop: '{{ find_sysctl_d.files }}'
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-84276-5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_ip_local_port_range

- name: Ensure sysctl net.ipv4.ip_local_port_range is set to 32768 65535
  sysctl:
    name: net.ipv4.ip_local_port_range
    value: 32768 65535
    sysctl_file: /etc/sysctl.conf
    state: present
    reload: true
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-84276-5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_ip_local_port_range

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

# Comment out any occurrences of net.ipv4.ip_local_port_range 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=$(grep -P '^(?!#).*[\s]*net.ipv4.ip_local_port_range.*$' $f | uniq )
  if ! test -z "$matching_list"; then
    while IFS= read -r entry; do
      escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
      # comment out "net.ipv4.ip_local_port_range" 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"


#
# Set runtime for net.ipv4.ip_local_port_range
#
/sbin/sysctl -q -n -w net.ipv4.ip_local_port_range="32768 65535"

#
# If net.ipv4.ip_local_port_range present in /etc/sysctl.conf, change value to "32768 65535"
#	else, add "net.ipv4.ip_local_port_range = 32768 65535" 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.ip_local_port_range")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "32768 65535"

# 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.ip_local_port_range\\>" "${SYSCONFIG_FILE}"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^net.ipv4.ip_local_port_range\\>.*/$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
    cce="CCE-84276-5"
    printf '# Per %s: Set %s in %s\n' "${cce}" "${formatted_output}" "${SYSCONFIG_FILE}" >> "${SYSCONFIG_FILE}"
    printf '%s\n' "$formatted_output" >> "${SYSCONFIG_FILE}"
fi

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

Set Kernel Parameter to Increase Local Port Range

Description

Rationale

Remediation - Ansible

Remediation - Shell Script