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).
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 [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; 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; 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
#
/sbin/sysctl -q -n -w kernel.yama.ptrace_scope="1"
#
# 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
cce="CCE-81058-0"
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
Ansible playbook
The following playbook can be run with Ansible to remediate the issue.
- name: List /etc/sysctl.d/*.conf files
find:
paths:
- /etc/sysctl.d/
- /run/sysctl.d/
- /usr/local/lib/sysctl.d/
contains: ^[\s]*kernel.yama.ptrace_scope.*$
patterns: '*.conf'
file_type: any
register: find_sysctl_d
when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- CCE-81058-0
- NIST-800-53-SC-7(10)
- disable_strategy
- low_complexity
- medium_disruption
- medium_severity
- reboot_required
- sysctl_kernel_yama_ptrace_scope
- name: Comment out any occurrences of kernel.yama.ptrace_scope from config files
replace:
path: '{{ item.path }}'
regexp: ^[\s]*kernel.yama.ptrace_scope
replace: '#kernel.yama.ptrace_scope'
loop: '{{ find_sysctl_d.files }}'
when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- CCE-81058-0
- NIST-800-53-SC-7(10)
- disable_strategy
- low_complexity
- medium_disruption
- medium_severity
- reboot_required
- sysctl_kernel_yama_ptrace_scope
- name: Ensure sysctl kernel.yama.ptrace_scope is set to 1
sysctl:
name: kernel.yama.ptrace_scope
value: '1'
sysctl_file: /etc/sysctl.conf
state: present
reload: true
when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
tags:
- CCE-81058-0
- NIST-800-53-SC-7(10)
- disable_strategy
- low_complexity
- medium_disruption
- medium_severity
- reboot_required
- sysctl_kernel_yama_ptrace_scope