Set SSH authentication attempt limit

An XCCDF Rule

Description

The MaxAuthTries parameter specifies the maximum number of authentication attempts permitted per connection. Once the number of failures reaches half this value, additional failures are logged. to set MaxAUthTries edit /etc/ssh/sshd_config as follows:

MaxAuthTries

Rationale

Setting the MaxAuthTries parameter to a low number will minimize the risk of successful brute force attacks to the SSH server.

ID: xccdf_org.ssgproject.content_rule_sshd_set_max_auth_tries
Severity: Medium
References: 0421 0422 0431 0974 1173 1401 1504 1505 1546 1557 1558 1559 1560 1561

2.2.6

5.1.16
Updated: about 1 month ago

Remediation Templates

- name: XCCDF Value sshd_max_auth_tries_value # promote to variable
  set_fact:
    sshd_max_auth_tries_value: !!str <xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_sshd_max_auth_tries_value" use="legacy"/>
  tags:
    - always
- name: Set SSH authentication attempt limit  block:

  - name: Check for duplicate values
    lineinfile:
      path: /etc/ssh/sshd_config
      create: true
      regexp: (?i)^\s*MaxAuthTries\s+
      state: absent
    check_mode: true
    changed_when: false
    register: dupes

  - name: Deduplicate values from /etc/ssh/sshd_config
    lineinfile:
      path: /etc/ssh/sshd_config
      create: true
      regexp: (?i)^\s*MaxAuthTries\s+
      state: absent
    when: dupes.found is defined and dupes.found > 1

  - name: Insert correct line to /etc/ssh/sshd_config
    lineinfile:
      path: /etc/ssh/sshd_config
      create: true
      regexp: (?i)^\s*MaxAuthTries\s+
      line: MaxAuthTries {{ sshd_max_auth_tries_value }}
      state: present
      insertbefore: BOF
      validate: /usr/sbin/sshd -t -f %s
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - PCI-DSSv4-2.2.6
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - restrict_strategy
  - sshd_set_max_auth_tries

# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then
sshd_max_auth_tries_value='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_sshd_max_auth_tries_value" use="legacy"/>'


if [ -e "/etc/ssh/sshd_config" ] ; then    
    LC_ALL=C sed -i "/^\s*MaxAuthTries\s\+/Id" "/etc/ssh/sshd_config"
else
    touch "/etc/ssh/sshd_config"
fi
# make sure file has newline at the end
sed -i -e '$a\' "/etc/ssh/sshd_config"

cp "/etc/ssh/sshd_config" "/etc/ssh/sshd_config.bak"
# Insert at the beginning of the file
printf '%s\n' "MaxAuthTries $sshd_max_auth_tries_value" > "/etc/ssh/sshd_config"
cat "/etc/ssh/sshd_config.bak" >> "/etc/ssh/sshd_config"
# Clean up after ourselves.
rm "/etc/ssh/sshd_config.bak"

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

Set SSH authentication attempt limit

Description

Rationale

Remediation Templates

An Ansible Snippet

A Shell Script