linux-baseline/controls/os_spec.rb

# frozen_string_literal: true

#
# Copyright:: 2015, Patrick Muench
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# author: Christoph Hartmann
# author: Dominik Richter
# author: Patrick Muench

login_defs_umask = input('login_defs_umask', value: os.redhat? ? '077' : '027')

login_defs_passmaxdays = input('login_defs_passmaxdays', value: '60')
login_defs_passmindays = input('login_defs_passmindays', value: '7')
login_defs_passwarnage = input('login_defs_passwarnage', value: '7')

shadow_group = 'root'
shadow_group = 'shadow' if os.debian? || os.suse? || os.name == 'alpine'
container_execution = begin
  virtualization.role == 'guest' && virtualization.system =~ /^(lxc|docker)$/
                      rescue NoMethodError
                        false
end

blacklist = input(
  'blacklist',
  value: suid_blacklist.default
)

cpuvulndir = '/sys/devices/system/cpu/vulnerabilities/'

# Overview of necessary mount options to be checked:
#
#---------------------------------------------------------
#   Mount point              nodev  noexec  nosuid
#   /boot                      v      v       v
#   /dev                              v       v
#   /dev/shm                   v      v       v
#   /home                      v              v
#   /run                       v              v
#   /tmp                       v      v       v
#   /var                       v              v
#   /var/log                   v      v       v
#   /var/log/audit             v      v       v
#   /var/tmp                   v      v       v
#---------------------------------------------------------

mount_exec_blocklist = input(
  'mount_exec_blocklist',
  value: ['/boot', '/dev', '/dev/shm', '/tmp', '/var/log', '/var/log/audit', '/var/tmp']
)

mount_suid_blocklist = input(
  'mount_suid_blocklist',
  value: ['/boot', '/dev', '/dev/shm', '/home', '/run', '/tmp', '/var', '/var/log', '/var/log/audit', '/var/tmp']
)

mount_dev_blocklist = input(
  'mount_dev_blocklist',
  value: ['/boot', '/dev/shm', '/home', '/run', '/tmp', '/var', '/var/log', '/var/log/audit', '/var/tmp']
)

control 'os-01' do
  impact 1.0
  title 'Trusted hosts login'
  desc "hosts.equiv file is a weak implementation of authentication. Disabling the hosts.equiv support helps to prevent users from subverting the system's normal access control mechanisms of the system."
  describe file('/etc/hosts.equiv') do
    it { should_not exist }
  end
end

control 'os-02' do
  impact 1.0
  title 'Check owner and permissions for /etc/shadow'
  desc 'Check periodically the owner and permissions for /etc/shadow'
  describe file('/etc/shadow') do
    it { should exist }
    it { should be_file }
    it { should be_owned_by 'root' }
    its('group') { should eq shadow_group }
    it { should_not be_executable }
    it { should_not be_readable.by('other') }
  end
  if os.redhat? || os.name == 'fedora'
    describe file('/etc/shadow') do
      it { should_not be_writable.by('owner') }
      it { should_not be_readable.by('owner') }
    end
  else
    describe file('/etc/shadow') do
      it { should be_writable.by('owner') }
      it { should be_readable.by('owner') }
    end
  end
  if os.debian? || os.suse?
    describe file('/etc/shadow') do
      it { should be_readable.by('group') }
    end
  else
    describe file('/etc/shadow') do
      it { should_not be_readable.by('group') }
    end
  end
end

control 'os-03' do
  impact 1.0
  title 'Check owner and permissions for /etc/passwd'
  desc 'Check periodically the owner and permissions for /etc/passwd'
  describe file('/etc/passwd') do
    it { should exist }
    it { should be_file }
    it { should be_owned_by 'root' }
    its('group') { should eq 'root' }
    it { should_not be_executable }
    it { should be_writable.by('owner') }
    it { should_not be_writable.by('group') }
    it { should_not be_writable.by('other') }
    it { should be_readable.by('owner') }
    it { should be_readable.by('group') }
    it { should be_readable.by('other') }
  end
end

control 'os-03b' do
  impact 1.0
  title 'Check passwords hashes in /etc/passwd'
  desc 'Check periodically that /etc/passwd does not contain passwords'
  describe passwd do
    its('passwords') { should be_in ['x', '*'] }
  end
end

control 'os-04' do
  impact 1.0
  title 'Dot in PATH variable'
  desc 'Do not include the current working directory in PATH variable. This makes it easier for an attacker to gain extensive rights by executing a Trojan program'
  describe os_env('PATH') do
    its('split') { should_not include('') }
    its('split') { should_not include('.') }
  end
end

control 'os-05' do
  impact 1.0
  title 'Check login.defs'
  desc 'Check owner and permissions for login.defs. Also check the configured PATH variable and umask in login.defs'
  describe file('/etc/login.defs') do
    it { should exist }
    it { should be_file }
    it { should be_owned_by 'root' }
    its('group') { should eq 'root' }
    it { should_not be_executable }
    it { should be_readable.by('owner') }
    it { should be_readable.by('group') }
    it { should be_readable.by('other') }
  end
  describe login_defs do
    its('ENV_SUPATH') { should include('/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin') }
    its('ENV_PATH') { should include('/usr/local/bin:/usr/bin:/bin') }
    its('UMASK') { should include(login_defs_umask) }
    its('PASS_MAX_DAYS') { should eq login_defs_passmaxdays }
    its('PASS_MIN_DAYS') { should eq login_defs_passmindays }
    its('PASS_WARN_AGE') { should eq login_defs_passwarnage }
    its('LOGIN_RETRIES') { should eq '5' }
    its('LOGIN_TIMEOUT') { should eq '60' }
    its('UID_MIN') { should eq '1000' }
    its('GID_MIN') { should eq '1000' }
  end
end

control 'os-05b' do
  impact 1.0
  title 'Check login.defs - RedHat specific'
  desc 'Check owner and permissions for login.defs. Also check the configured PATH variable and umask in login.defs'
  describe file('/etc/login.defs') do
    it { should_not be_writable }
  end
  describe login_defs do
    its('SYS_UID_MIN') { should eq '201' }
    its('SYS_UID_MAX') { should eq '999' }
    its('SYS_GID_MIN') { should eq '201' }
    its('SYS_GID_MAX') { should eq '999' }
  end
  only_if { os.redhat? }
end

control 'os-06' do
  impact 1.0
  title 'Check for SUID/ SGID blacklist'
  desc 'Find blacklisted SUID and SGID files to ensure that no rogue SUID and SGID files have been introduced into the system'

  describe suid_check(blacklist) do
    its('diff') { should be_empty }
  end
end

control 'os-07' do
  impact 1.0
  title 'Unique uid and gid'
  desc 'Check for unique uids gids'
  describe passwd do
    its('uids') { should_not contain_duplicates }
  end
  describe etc_group do
    its('gids') { should_not contain_duplicates }
  end
end

control 'os-09' do
  impact 1.0
  title 'Check for .rhosts and .netrc file'
  desc 'Find .rhosts and .netrc files - CIS Benchmark 9.2.9-10'
  output = command('find / -maxdepth 3 \( -iname .rhosts -o -iname .netrc \) -print 2>/dev/null | grep -v \'^find:\'')
  out = output.stdout.split(/\r?\n/)
  describe out do
    it { should be_empty }
  end
end

control 'os-10' do
  impact 1.0
  title 'CIS: Disable unused filesystems'
  desc '1.1.1 Ensure mounting of cramfs, freevxfs, jffs2, hfs, hfsplus, squashfs, udf, FAT'
  only_if { !container_execution }
  efi_dir = inspec.file('/sys/firmware/efi')
  describe file('/etc/modprobe.d/dev-sec.conf') do
    its(:content) { should match 'install cramfs /bin/true' }
    its(:content) { should match 'install freevxfs /bin/true' }
    its(:content) { should match 'install jffs2 /bin/true' }
    its(:content) { should match 'install hfs /bin/true' }
    its(:content) { should match 'install hfsplus /bin/true' }
    # Ubuntu Snaps need SquashFS to function
    unless service('snapd').running?
      its(:content) { should match 'install squashfs /bin/true' }
    end
    its(:content) { should match 'install udf /bin/true' }
    # if efi is active, do not disable vfat. otherwise the system
    # won't boot anymore
    unless efi_dir.exist?
      its(:content) { should match 'install vfat /bin/true' }
    end
  end
end

control 'os-11' do
  impact 1.0
  title 'Protect log-directory'
  desc 'The log-directory /var/log should belong to root'
  describe file('/var/log') do
    it { should be_directory }
    it { should be_owned_by 'root' }
    its(:group) { should match(/^root|syslog$/) }
  end
end

control 'os-12' do
  impact 1.0
  title 'Detect vulnerabilities in the cpu-vulnerability-directory'
  desc 'Check for known cpu vulnerabilities described here: https://www.kernel.org/doc/html/v5.6/admin-guide/hw-vuln/index.html'
  only_if { !container_execution }

  if file(cpuvulndir).exist?
    describe file(cpuvulndir) do
      it { should be_directory }
    end

    loaded_files = command("find #{cpuvulndir} -type f -maxdepth 1").stdout.split(/\n/).map(&:strip).find_all { |vulnfiles| !vulnfiles.empty? }

    loaded_files.each do |vulnfile|
      describe file(vulnfile) do
        its(:content) { should_not match 'vulnerable' }
        its(:content) { should_not match 'Vulnerable' }
      end
    end
  end
end

control 'os-13' do
  impact 1.0
  title 'Protect cron directories and files'
  desc 'The cron directories and files should belong to root.'

  cron_files = ['/etc/crontab', '/etc/cron.hourly', '/etc/cron.daily', '/etc/cron.weekly', '/etc/cron.monthly', '/etc/cron.d']

  cron_files.each do |cron_file|
    next unless file(cron_file).exist?

    describe file(cron_file) do
      it { should be_owned_by 'root' }
      it { should_not be_writable.by('group') }
      it { should_not be_writable.by('other') }
      it { should_not be_readable.by('group') }
      it { should_not be_readable.by('other') }
    end
  end
end

control 'os-14' do
  impact 1.0
  title 'Check mountpoints for noexec mount options'
  desc 'Use the noexec mount options to limit attack vectors via mount points'

  mount_exec_blocklist.each do |mnt_point|
    next unless mount(mnt_point).mounted?

    describe mount(mnt_point) do
      its('options') { should include('noexec') }
    end
  end
end

control 'os-15' do
  impact 1.0
  title 'Check mountpoints for nosuid mount options'
  desc 'Use the nosuid mount options to limit attack vectors via mount points'

  mount_suid_blocklist.each do |mnt_point|
    next unless mount(mnt_point).mounted?

    describe mount(mnt_point) do
      its('options') { should include('nosuid') }
    end
  end
end

control 'os-16' do
  impact 1.0
  title 'Check mountpoints for nodev mount options'
  desc 'Use the nodev mount options to limit attack vectors via mount points'

  mount_dev_blocklist.each do |mnt_point|
    next unless mount(mnt_point).mounted?

    describe mount(mnt_point) do
      its('options') { should include('nodev') }
    end
  end
end