Restrict usage of ptrace to descendant processes

Docs > Datadog Security > OOTB Rules > Restrict usage of ptrace to descendant processes

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Description

To set the runtime status of the kernel.yama.ptrace_scope kernel parameter, run the following command:

$ sudo sysctl -w kernel.yama.ptrace_scope=1

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

kernel.yama.ptrace_scope = 1

Rationale

Unrestricted usage of ptrace allows compromised binaries to run ptrace on another processes of the user. Like this, the attacker can steal sensitive information from the target processes (e.g. SSH sessions, web browser, …) without any additional assistance from the user (i.e. without resorting to phishing).

Remediation

Shell script

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

#!/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

# Comment out any occurrences of kernel.yama.ptrace_scope 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

  matching_list=$(grep -P '^(?!#).*[\s]*kernel.yama.ptrace_scope.*$' $f | uniq )
  if ! test -z "$matching_list"; then
    while IFS= read -r entry; do
      escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
      # comment out "kernel.yama.ptrace_scope" matches to preserve user data
      sed -i --follow-symlinks "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 kernel.yama.ptrace_scope
#
if ! /bin/false ; then
    /sbin/sysctl -q -n -w kernel.yama.ptrace_scope="1"
fi

#
# If kernel.yama.ptrace_scope present in /etc/sysctl.conf, change value to "1"
#	else, add "kernel.yama.ptrace_scope = 1" 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' <<< "^kernel.yama.ptrace_scope")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "1"

# 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 "^kernel.yama.ptrace_scope\\>" "${SYSCONFIG_FILE}"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^kernel.yama.ptrace_scope\\>.*/$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

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

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - 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:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - Find all files that contain
    kernel.yama.ptrace_scope
  ansible.builtin.shell:
    cmd: find -L {{ sysctl_paths | join(" ") }} -type f -name '*.conf' | xargs grep
      -HP '^\s*kernel.yama.ptrace_scope\s*=\s*.*$'
  register: find_all_values
  check_mode: false
  changed_when: false
  failed_when: false
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - Find all files that set
    kernel.yama.ptrace_scope to correct value
  ansible.builtin.shell:
    cmd: find -L {{ sysctl_paths | join(" ") }} -type f -name '*.conf' | xargs grep
      -HP '^\s*kernel.yama.ptrace_scope\s*=\s*1$'
  register: find_correct_value
  check_mode: false
  changed_when: false
  failed_when: false
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - Comment out any occurrences
    of kernel.yama.ptrace_scope from config files
  ansible.builtin.replace:
    path: '{{ item | split(":") | first }}'
    regexp: ^[\s]*kernel.yama.ptrace_scope
    replace: '#kernel.yama.ptrace_scope'
  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:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - Comment out any occurrences
    of kernel.yama.ptrace_scope from /etc/ufw/sysctl.conf
  ansible.builtin.replace:
    path: /etc/ufw/sysctl.conf
    regexp: (^[\s]*kernel.yama.ptrace_scope.*$)
    replace: '# \1'
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope

- name: Restrict usage of ptrace to descendant processes - Ensure sysctl kernel.yama.ptrace_scope
    is set to 1
  ansible.posix.sysctl:
    name: kernel.yama.ptrace_scope
    value: '1'
    sysctl_file: /etc/sysctl.conf
    state: present
    reload: true
  when: '"linux-base" in ansible_facts.packages'
  tags:
  - NIST-800-53-SC-7(10)
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_yama_ptrace_scope