smtp-user-enum

Username guessing tool primarily for use against the default Solaris SMTP service. Can use either EXPN, VRFY or RCPT TO.  Recent changes are detailed in the CHANGELOG.

Download smtp-user-enum v1.2 here.

MD5 and SHA1 checksums are the packages can be downloaded.  They’re based on the package name (below v.v represents the version, e.g. 1.1):

http://pentestmonkey.net/tools/smtp-user-enum/smtp-user-enum-v.v-beta.tar.gz.md5

http://pentestmonkey.net/tools/smtp-user-enum/smtp-user-enum-v.v-beta.tar.gz.sha1

User documentation is also available in PDF format.

 

smtp-user-enum User Documentation

 

Contents

  • Overview
  • Installation
  • Usage
  • Some Examples
    • Using the SMTP VRFY Command
    • Using the SMTP EXPN Command
    • Using the SMTP RCPT TO Command
    • Enumerating Email Addresses Instead of Usernames
  • License

 

Overview

smtp-user-enum is a tool for enumerating OS-level user accounts on Solaris via the SMTP service (sendmail). Enumeration is performed by inspecting the responses to VRFY, EXPN and RCPT TO commands. It could be adapted to work against other vulnerable SMTP daemons, but this hasn’t been done as of v1.0.

Installation

smtp-user-enum is just a stand alone PERL script, so installation is as simple as copying it to your path (e.g. /usr/local/bin). It has only been tested under Linux so far.

It depends on the following PERL modules which you may need to install first:

  • Socket
  • IO::Handle
  • IO::Select
  • IO::Socket::INET
  • Getopt::Std

If you have PERL installed, you should be able to install the modules from CPAN:

 # perl -MCPAN -e shell
 cpan> install Getopt::Std

Usage

smtp-user-enum simply needs to be passed a list of users and at least one target running an SMTP service.

 smtp-user-enum v1.0 ( http://pentestmonkey.net/tools/smtp-user-enum ) 

 Usage: smtp-user-enum.pl [options] (-u username|-U file-of-usernames) (-t host|-T file-of-targets) 

 options are:
         -m n     Maximum number of processes (default: 5)
         -M mode  Method to use for username guessing EXPN, VRFY or RCPT (default: VRFY)
         -u user  Check if user exists on remote system
         -f addr  From email address to use for "RCPT TO" guessing (default: user@example.com)
        -D dom   Domain to append to supplied user list to make email addresses (Default: none)
                 Use this option when you want to guess valid email addresses instead of just usernames
                 e.g. "-D example.com" would guess foo@example.com, bar@example.com, etc.  Instead of
                      simply the usernames foo and bar.
         -U file  File of usernames to check via smtp service
         -t host  Server host running smtp service
         -T file  File of hostnames running the smtp service
         -p port  TCP port on which smtp service runs (default: 25)
         -d       Debugging output
         -t n     Wait a maximum of n seconds for reply (default: 5)
         -v       Verbose
         -h       This help message

Some Examples

For all of the examples below we need a list of potential usernames. The following output demostrates the format for this list:

 $ head users.txt
 root
 bin
 daemon
 adm
 lp
 sync
 shutdown
 halt
 mail
 news

Using the SMTP VRFY Command

The output below shows how the SMTP server responds differently to VRFY requests for valid and invalid users. It is recommended that a manual check like the following is carried out before running smtp-user-enum. Obviously the tool won’t work if the server doesn’t respond differently to requests for valid and invalid users.

 $ telnet 10.0.0.1 25
 Trying 10.0.0.1...
 Connected to 10.0.0.1.
 Escape character is '^]'.
 220 myhost ESMTP Sendmail 8.9.3
 HELO
 501 HELO requires domain address
 HELO x
 250 myhost Hello [10.0.0.99], pleased to meet you
 VRFY root
 250 Super-User <root@myhost>
 VRFY blah
 550 blah... User unknown

To use smtp-user-enum to enumerate valid usernames using the VRFY command, first prepare a list of usernames (users.txt) and run the tool as follows:

 $ smtp-user-enum.pl -M VRFY -U users.txt -t 10.0.0.1
 Starting smtp-user-enum v1.0 ( http://pentestmonkey.net/tools/smtp-user-enum ) 

  ----------------------------------------------------------
 |                   Scan Information                       |
  ---------------------------------------------------------- 

 Mode ..................... VRFY
 Worker Processes ......... 5
 Usernames file ........... users.txt
 Target count ............. 1
 Username count ........... 47
 Target TCP port .......... 25
 Query timeout ............ 5 secs
 Relay Server ............. Not used 

 ######## Scan started at Sun Jan 21 18:01:50 2007 #########
 root@10.0.0.1: Exists
 bin@10.0.0.1: Exists
 daemon@10.0.0.1: Exists
 lp@10.0.0.1: Exists
 adm@10.0.0.1: Exists
 uucp@10.0.0.1: Exists
 postmaster@10.0.0.1: Exists
 nobody@10.0.0.1: Exists
 ftp@10.0.0.1: Exists
 ######## Scan completed at Sun Jan 21 18:01:50 2007 #########
 9 results. 

 47 queries in 1 seconds (47.0 queries / sec)

It’s worth noting that postmaster is not actually a valid OS-level user account – it’s a mail alias.

Using the SMTP EXPN Command

The output below shows how the SMTP server responds differently to EXPN requests for valid and invalid users.

 $ telnet 10.0.0.1 25
 Trying 10.0.0.1...
 Connected to 10.0.0.1.
 Escape character is '^]'.
 220 myhost ESMTP Sendmail 8.9.3
 HELO
 501 HELO requires domain address
 HELO x
 250 myhost Hello [10.0.0.99], pleased to meet you
 EXPN root
 250 Super-User <root@myhost>
 EXPN blah
 550 blah... User unknown

To use smtp-user-enum to enumerate valid usernames using the VRFY command, first prepare a list of usernames (users.txt) and run the tool as follows (unsurprisingly, we get the same results as above):

 $ smtp-user-enum.pl -M EXPN -U users.txt -t 10.0.0.1
 Starting smtp-user-enum v1.0 ( http://pentestmonkey.net/tools/smtp-user-enum ) 

  ----------------------------------------------------------
 |                   Scan Information                       |
  ---------------------------------------------------------- 

 Mode ..................... EXPN
 Worker Processes ......... 5
 Usernames file ........... users.txt
 Target count ............. 1
 Username count ........... 47
 Target TCP port .......... 25
 Query timeout ............ 5 secs
 Relay Server ............. Not used 

 ######## Scan started at Sun Jan 21 18:01:50 2007 #########
 root@10.0.0.1: Exists
 bin@10.0.0.1: Exists
 daemon@10.0.0.1: Exists
 lp@10.0.0.1: Exists
 adm@10.0.0.1: Exists
 uucp@10.0.0.1: Exists
 postmaster@10.0.0.1: Exists
 nobody@10.0.0.1: Exists
 ftp@10.0.0.1: Exists
 ######## Scan completed at Sun Jan 21 18:01:50 2007 #########
 9 results. 

 47 queries in 1 seconds (47.0 queries / sec)

Using the SMTP RCPT TO Command

The output below shows how the SMTP server responds differently to RCPT TO requests for valid and invalid users. This is often to the most useful technique as VRFY and EXPN are often disabled to prevent username enumeration.

 $ telnet 10.0.0.1 25
 Trying 10.0.0.1...
 Connected to 10.0.0.1.
 Escape character is '^]'.
 220 myhost ESMTP Sendmail 8.9.3
 HELO
 501 HELO requires domain address
 HELO x
 250 myhost Hello [10.0.0.99], pleased to meet you
 MAIL FROM:root
 250 root... Sender ok
 RCPT TO:root
 250 root... Recipient ok
 RCPT TO: blah
 550 blah... User unknown

To use smtp-user-enum to enumerate valid usernames using the RCPT TO command, first prepare a list of usernames (users.txt) and run the tool as follows (again, the results are the same as above):

 $ smtp-user-enum.pl -M RCPT -U users.txt -t 10.0.0.1
 Starting smtp-user-enum v1.0 ( http://pentestmonkey.net/tools/smtp-user-enum ) 

  ----------------------------------------------------------
 |                   Scan Information                       |
  ---------------------------------------------------------- 

 Mode ..................... RCPT
 Worker Processes ......... 5
 Usernames file ........... users.txt
 Target count ............. 1
 Username count ........... 47
 Target TCP port .......... 25
 Query timeout ............ 5 secs
 Relay Server ............. Not used 

 ######## Scan started at Sun Jan 21 18:01:50 2007 #########
 root@10.0.0.1: Exists
 bin@10.0.0.1: Exists
 daemon@10.0.0.1: Exists
 lp@10.0.0.1: Exists
 adm@10.0.0.1: Exists
 uucp@10.0.0.1: Exists
 postmaster@10.0.0.1: Exists
 nobody@10.0.0.1: Exists
 ftp@10.0.0.1: Exists
 ######## Scan completed at Sun Jan 21 18:01:50 2007 #########
 9 results. 

 47 queries in 1 seconds (47.0 queries / sec)

Enumerating Email Addresses Instead of Usernames

Version 1.1 adds support for optionally appending a domain name to the end of each username:

$ ./smtp-user-enum.pl -D example.com -M RCPT -U users.txt -t 10.0.0.1
Starting smtp-user-enum v1.1 ( http://pentestmonkey.net/tools/smtp-user-enum )
 ----------------------------------------------------------
|                   Scan Information                       |
 ----------------------------------------------------------
Mode ..................... RCPT
Worker Processes ......... 5
Usernames file ........... users.txt
Target count ............. 1
Username count ........... 47
Target TCP port .......... 25
Query timeout ............ 5 secs
Target domain ............ example.com

 

######## Scan started at Wed Jan 16 20:43:58 2008 #########
10.0.0.1: bin@example.com exists
10.0.0.1: daemon@example.com exists
10.0.0.1: root@example.com exists
10.0.0.1: postmaster@example.com exists
######## Scan completed at Wed Jan 16 20:43:58 2008 #########
4 results.
7 queries in 1 seconds (47.0 queries / sec)

License

This tool may be used for legal purposes only. Users take full responsibility for any actions performed using this tool. The author accepts no liability for damage caused by this tool. If these terms are not acceptable to you, then do not use this tool.

In all other respects the GPL version 2 applies:

 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License version 2 as
 published by the Free Software Foundation. 

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details. 

 You should have received a copy of the GNU General Public License along
 with this program; if not, write to the Free Software Foundation, Inc.,
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

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Posted in User Enumeration