---
title: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > OOTB Rules > Disable Kernel Parameter for Sending
  ICMP Redirects on all IPv4 Interfaces
---

> For the complete documentation index, see [llms.txt](https://docs.datadoghq.com/llms.txt).

# Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
 
## Description{% #description %}

To set the runtime status of the `net.ipv4.conf.all.send_redirects` kernel parameter, run the following command:

```
$ sudo sysctl -w net.ipv4.conf.all.send_redirects=0
```

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

```
net.ipv4.conf.all.send_redirects = 0
```

## Rationale{% #rationale %}

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.

The ability to send ICMP redirects is only appropriate for systems acting as routers.

## Remediation{% #remediation %}

### Shell script{% #shell-script %}

The following script can be run on the host to remediate the issue.

```bash
#!/bin/bash

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

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

SYSCONFIG_FILE="/etc/sysctl.conf"


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

for f in /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /etc/ufw/sysctl.conf; do


  # skip systemd-sysctl symlink (/etc/sysctl.d/99-sysctl.conf -> /etc/sysctl.conf)
  if [[ "$(readlink -f "$f")" == "/etc/sysctl.conf" ]]; then continue; fi

  if [[ "$(readlink -f "$f")" == "$(readlink -f "${SYSCONFIG_FILE}")" ]]; then
    # entries starting with net.ipv4.conf.all.send_redirects in the file this remediation writes to
    # are replaced in place below, commenting them out would make the remediation non-idempotent
    matching_list=$(grep -P '^(?!#)(?!net.ipv4.conf.all.send_redirects\b).*[\s]*net.ipv4.conf.all.send_redirects.*$' $f | uniq )
  else
    matching_list=$(grep -P '^(?!#).*[\s]*net.ipv4.conf.all.send_redirects.*$' $f | uniq )
  fi
  if ! test -z "$matching_list"; then
    while IFS= read -r entry; do
      escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
      # comment out "net.ipv4.conf.all.send_redirects" matches to preserve user data
      sed -i --follow-symlinks "s/^${escaped_entry}$/# &/g" $f
    done <<< "$matching_list"
  fi
done

#
# Set runtime for net.ipv4.conf.all.send_redirects
#
if ! /bin/false ; then
    /sbin/sysctl -q -n -w net.ipv4.conf.all.send_redirects="0"
fi

#
# If net.ipv4.conf.all.send_redirects present in /etc/sysctl.conf, change value to "0"
#	else, add "net.ipv4.conf.all.send_redirects = 0" 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.conf.all.send_redirects")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "0"

# 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.conf.all.send_redirects\\>" "${SYSCONFIG_FILE}"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^net.ipv4.conf.all.send_redirects\\>.*/$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
```

### Ansible playbook{% #ansible-playbook %}

The following playbook can be run with Ansible to remediate the issue.

```gdscript3
- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Set fact for sysctl paths
  ansible.builtin.set_fact:
    sysctl_paths:
    - /etc/sysctl.d/
    - /run/sysctl.d/
    - /usr/local/lib/sysctl.d/
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Find all files that contain net.ipv4.conf.all.send_redirects
  ansible.builtin.shell:
    cmd: |-
      set -o pipefail
      find -L {{ sysctl_paths | join(" ") }} -type f -name '*.conf' | xargs grep -HP '^\s*net.ipv4.conf.all.send_redirects\s*=\s*.*$'
    executable: /bin/bash
  register: find_all_values
  check_mode: false
  changed_when: false
  failed_when: false
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Find all files that set net.ipv4.conf.all.send_redirects to correct value
  ansible.builtin.shell:
    cmd: |-
      set -o pipefail
      find -L {{ sysctl_paths | join(" ") }} -type f -name '*.conf' | xargs grep -HP '^\s*net.ipv4.conf.all.send_redirects\s*=\s*0$'
    executable: /bin/bash
  register: find_correct_value
  check_mode: false
  changed_when: false
  failed_when: false
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Comment out any occurrences of net.ipv4.conf.all.send_redirects from config
    files
  ansible.builtin.replace:
    path: '{{ item | split(":") | first }}'
    regexp: ^[\s]*net.ipv4.conf.all.send_redirects
    replace: '#net.ipv4.conf.all.send_redirects'
  loop: '{{ find_all_values.stdout_lines }}'
  when:
  - '"linux-base" in ansible_facts.packages'
  - find_correct_value.stdout_lines | length == 0 or find_all_values.stdout_lines
    | length > find_correct_value.stdout_lines | length
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Comment out any occurrences of net.ipv4.conf.all.send_redirects from /etc/ufw/sysctl.conf
  ansible.builtin.replace:
    path: /etc/ufw/sysctl.conf
    regexp: (^[\s]*net.ipv4.conf.all.send_redirects.*$)
    replace: '# \1'
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects

- name: Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces
    - Ensure sysctl net.ipv4.conf.all.send_redirects is set to 0
  ansible.posix.sysctl:
    name: net.ipv4.conf.all.send_redirects
    value: '0'
    sysctl_file: /etc/sysctl.conf
    state: present
    reload: true
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - CJIS-5.10.1.1
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-SC-5
  - NIST-800-53-SC-7(a)
  - PCI-DSSv4-1.4
  - PCI-DSSv4-1.4.5
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_net_ipv4_conf_all_send_redirects
```