Ensure SSH MaxStartups is configured
このページは日本語には対応しておりません。随時翻訳に取り組んでいます。
翻訳に関してご質問やご意見ございましたら、
お気軽にご連絡ください。
Description
The MaxStartups parameter specifies the maximum number of concurrent unauthenticated
connections to the SSH daemon. Additional connections will be dropped until authentication
succeeds or the LoginGraceTime expires for a connection. To configure MaxStartups, you should
add or edit the following line in the /etc/ssh/sshd_config
file:
Rationale
To protect a system from denial of service due to a large number of pending authentication
connection attempts, use the rate limiting function of MaxStartups to protect availability of
sshd logins and prevent overwhelming the daemon.
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='${db:Status-Status}
' 'kernel' 2>/dev/null | grep -q installed; then
var_sshd_set_maxstartups='10:30:60'
mkdir -p /etc/ssh/sshd_config.d
touch /etc/ssh/sshd_config.d/00-complianceascode-hardening.conf
LC_ALL=C sed -i "/^\s*MaxStartups\s\+/Id" "/etc/ssh/sshd_config"
LC_ALL=C sed -i "/^\s*MaxStartups\s\+/Id" "/etc/ssh/sshd_config.d"/*.conf
if [ -e "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf" ] ; then
LC_ALL=C sed -i "/^\s*MaxStartups\s\+/Id" "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf"
else
touch "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf"
fi
# make sure file has newline at the end
sed -i -e '$a\' "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf"
cp "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf" "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf.bak"
# Insert at the beginning of the file
printf '%s\n' "MaxStartups $var_sshd_set_maxstartups" > "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf"
cat "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf.bak" >> "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf"
# Clean up after ourselves.
rm "/etc/ssh/sshd_config.d/00-complianceascode-hardening.conf.bak"
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:
- PCI-DSSv4-2.2
- PCI-DSSv4-2.2.6
- low_complexity
- low_disruption
- medium_severity
- no_reboot_needed
- restrict_strategy
- sshd_set_maxstartups
- name: XCCDF Value var_sshd_set_maxstartups # promote to variable
set_fact:
var_sshd_set_maxstartups: !!str 10:30:60
tags:
- always
- name: Ensure SSH MaxStartups is configured
block:
- name: Deduplicate values from /etc/ssh/sshd_config
lineinfile:
path: /etc/ssh/sshd_config
create: false
regexp: (?i)(?i)^\s*{{ "MaxStartups"| regex_escape }}\s+
state: absent
- name: Check if /etc/ssh/sshd_config.d exists
stat:
path: /etc/ssh/sshd_config.d
register: _etc_ssh_sshd_config_d_exists
- name: Check if the parameter MaxStartups is present in /etc/ssh/sshd_config.d
find:
paths: /etc/ssh/sshd_config.d
recurse: 'yes'
follow: 'no'
contains: (?i)^\s*{{ "MaxStartups"| regex_escape }}\s+
register: _etc_ssh_sshd_config_d_has_parameter
when: _etc_ssh_sshd_config_d_exists.stat.isdir is defined and _etc_ssh_sshd_config_d_exists.stat.isdir
- name: Remove parameter from files in /etc/ssh/sshd_config.d
lineinfile:
path: '{{ item.path }}'
create: false
regexp: (?i)(?i)^\s*{{ "MaxStartups"| regex_escape }}\s+
state: absent
with_items: '{{ _etc_ssh_sshd_config_d_has_parameter.files }}'
when: _etc_ssh_sshd_config_d_has_parameter.matched
- name: Insert correct line to /etc/ssh/sshd_config.d/00-complianceascode-hardening.conf
lineinfile:
path: /etc/ssh/sshd_config.d/00-complianceascode-hardening.conf
create: true
regexp: (?i)(?i)^\s*{{ "MaxStartups"| regex_escape }}\s+
line: MaxStartups {{ var_sshd_set_maxstartups }}
state: present
insertbefore: BOF
validate: /usr/sbin/sshd -t -f %s
when: '"kernel" in ansible_facts.packages'
tags:
- PCI-DSSv4-2.2
- PCI-DSSv4-2.2.6
- low_complexity
- low_disruption
- medium_severity
- no_reboot_needed
- restrict_strategy
- sshd_set_maxstartups