SMTP Open Relay Detection - Metasploit


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

Table Of Contents
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Module Overview

Name: SMTP Open Relay Detection
Module: auxiliary/scanner/smtp/smtp_relay
Source code: modules/auxiliary/scanner/smtp/smtp_relay.rb
Disclosure date: -
Last modification time: 2017-07-24 06:26:21 +0000
Supported architecture(s): -
Supported platform(s): -
Target service / protocol: smtp, smtps
Target network port(s): 25, 465, 587, 2525, 25000, 25025
List of CVEs: -

This module tests if an SMTP server will accept (via a code 250) an e-mail by using a variation of testing methods. Some of the extended methods will try to abuse configuration or mailserver flaws.

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

This module is a scanner module, and is capable of testing against multiple hosts.

msf > use auxiliary/scanner/smtp/smtp_relay
msf auxiliary(smtp_relay) > show options
    ... show and set options ...
msf auxiliary(smtp_relay) > set RHOSTS ip-range
msf auxiliary(smtp_relay) > exploit

Other examples of setting the RHOSTS option:

Example 1:

msf auxiliary(smtp_relay) > set RHOSTS 192.168.1.3-192.168.1.200

Example 2:

msf auxiliary(smtp_relay) > set RHOSTS 192.168.1.1/24

Example 3:

msf auxiliary(smtp_relay) > set RHOSTS file:/tmp/ip_list.txt

Required Options

  • RHOSTS: The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'

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Msfconsole Usage

Here is how the scanner/smtp/smtp_relay auxiliary module looks in the msfconsole:

msf6 > use auxiliary/scanner/smtp/smtp_relay

msf6 auxiliary(scanner/smtp/smtp_relay) > show info

       Name: SMTP Open Relay Detection
     Module: auxiliary/scanner/smtp/smtp_relay
    License: Metasploit Framework License (BSD)
       Rank: Normal

Provided by:
  Campbell Murray
  xistence <[email protected]>

Check supported:
  No

Basic options:
  Name      Current Setting     Required  Description
  ----      ---------------     --------  -----------
  EXTENDED  false               yes       Do all the 16 extended checks
  MAILFROM  [email protected]  yes       FROM address of the e-mail
  MAILTO    [email protected]  yes       TO address of the e-mail
  RHOSTS                        yes       The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
  RPORT     25                  yes       The target port (TCP)
  THREADS   1                   yes       The number of concurrent threads (max one per host)

Description:
  This module tests if an SMTP server will accept (via a code 250) an 
  e-mail by using a variation of testing methods. Some of the extended 
  methods will try to abuse configuration or mailserver flaws.

References:
  http://www.ietf.org/rfc/rfc2821.txt
  https://svn.nmap.org/nmap/scripts/smtp-open-relay.nse

Module Options

This is a complete list of options available in the scanner/smtp/smtp_relay auxiliary module:

msf6 auxiliary(scanner/smtp/smtp_relay) > show options

Module options (auxiliary/scanner/smtp/smtp_relay):

   Name      Current Setting     Required  Description
   ----      ---------------     --------  -----------
   EXTENDED  false               yes       Do all the 16 extended checks
   MAILFROM  [email protected]  yes       FROM address of the e-mail
   MAILTO    [email protected]  yes       TO address of the e-mail
   RHOSTS                        yes       The target host(s), range CIDR identifier, or hosts file with syntax 'file:<path>'
   RPORT     25                  yes       The target port (TCP)
   THREADS   1                   yes       The number of concurrent threads (max one per host)

Advanced Options

Here is a complete list of advanced options supported by the scanner/smtp/smtp_relay auxiliary module:

msf6 auxiliary(scanner/smtp/smtp_relay) > show advanced

Module advanced options (auxiliary/scanner/smtp/smtp_relay):

   Name                 Current Setting  Required  Description
   ----                 ---------------  --------  -----------
   CHOST                                 no        The local client address
   CPORT                                 no        The local client port
   ConnectTimeout       10               yes       Maximum number of seconds to establish a TCP connection
   Proxies                               no        A proxy chain of format type:host:port[,type:host:port][...]
   SSL                  false            no        Negotiate SSL/TLS for outgoing connections
   SSLCipher                             no        String for SSL cipher - "DHE-RSA-AES256-SHA" or "ADH"
   SSLVerifyMode        PEER             no        SSL verification method (Accepted: CLIENT_ONCE, FAIL_IF_NO_PEER_CERT, NONE, PEER)
   SSLVersion           Auto             yes       Specify the version of SSL/TLS to be used (Auto, TLS and SSL23 are auto-negotiate) (Accepted: Auto, TLS, SSL23, SSL3, TLS1, TLS1.1, TLS1.2)
   ShowProgress         true             yes       Display progress messages during a scan
   ShowProgressPercent  10               yes       The interval in percent that progress should be shown
   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 scanner/smtp/smtp_relay module can do:

msf6 auxiliary(scanner/smtp/smtp_relay) > show actions

Auxiliary actions:

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

Evasion Options

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

msf6 auxiliary(scanner/smtp/smtp_relay) > show evasion

Module evasion options:

   Name                Current Setting  Required  Description
   ----                ---------------  --------  -----------
   TCP::max_send_size  0                no        Maxiumum tcp segment size.  (0 = disable)
   TCP::send_delay     0                no        Delays inserted before every send.  (0 = disable)

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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.

Unable to establish an SMTP session

Here is a relevant code snippet related to the "Unable to establish an SMTP session" error message:

71:	        do_test_relay(16, "MAIL FROM:<#{mailfromuser}@[#{rhost}]>", "RCPT TO:<#{mailtodomain}!#{mailtouser}@#{serverhost}>")
72:	      else
73:	        do_test_relay(nil, "MAIL FROM:<#{datastore['MAILFROM']}>", "RCPT TO:<#{datastore['MAILTO']}>")
74:	    end
75:	    rescue
76:	      print_error("Unable to establish an SMTP session")
77:	      return
78:	    end
79:	  end
80:	
81:	  def do_test_relay(testnumber, mailfrom, mailto)

No relay detected

Here is a relevant code snippet related to the "No relay detected" error message:

103:	        else
104:	          print_good("Test ##{testnumber} - Potential open SMTP relay detected: - #{mailfrom} -> #{mailto}")
105:	        end
106:	      else
107:	        if testnumber.nil?
108:	          print_status "No relay detected"
109:	        else
110:	          print_status "Test ##{testnumber} - No relay detected"
111:	        end
112:	      end
113:

Test #<TESTNUMBER> - No relay detected

Here is a relevant code snippet related to the "Test #<TESTNUMBER> - No relay detected" error message:

105:	        end
106:	      else
107:	        if testnumber.nil?
108:	          print_status "No relay detected"
109:	        else
110:	          print_status "Test ##{testnumber} - No relay detected"
111:	        end
112:	      end
113:	
114:	    rescue
115:	      print_error("Test ##{testnumber} - Unable to establish an SMTP session")

Test #<TESTNUMBER> - Unable to establish an SMTP session

Here is a relevant code snippet related to the "Test #<TESTNUMBER> - Unable to establish an SMTP session" error message:

109:	        else
110:	          print_status "Test ##{testnumber} - No relay detected"
111:	        end
112:	      end
113:	
114:	    rescue
115:	      print_error("Test ##{testnumber} - Unable to establish an SMTP session")
116:	      return
117:	    end
118:	  end
119:	end

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References

See Also

Check also the following modules related to this module:

Authors

  • Campbell Murray
  • xistence <xistence[at]0x90.nl>

Version

This page has been produced using Metasploit Framework version 6.1.27-dev. For more modules, visit the Metasploit Module Library.

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