SMTP user enumeration tool with clever timeout, retry and reconnect functionality.
Project description
smtp-user-enum
SMTP user enumeration via VRFY, EXPN and RCPT with clever timeout, retry and reconnect functionality.
Some SMTP server take a long time for initial communication (banner and greeting) and then handle subsequent commands quite fast. Then again they randomly start to get slow again.
This implementation of SMTP user enumeration counteracts with granular timeout, retry and reconnect options for initial communication and enumeration separately. The defaults should work fine, however if you encounter slow enumeration, adjust the settings according to your needs.
Additionally if it encounters anything like 421 Too many errors on this connection it will
automatically and transparently reconnect and continue from where it left off.
Inspired by smtp-user-enum Perl script and rewritten in Python with full Python2 and Python3 support.
Installation
pip install smtp-user-enum
Usage
$ smtp-user-enum --help
SMTP user enumeration tool with clever timeout, retry and reconnect functionality.
Some SMTP server take a long time for initial communication (banner and greeting) and then
handle subsequent commands quite fast. Then again they randomly start to get slow again.
This implementation of SMTP user enumeration counteracts with granular timeout, retry and
reconnect options for initial communication and enumeration separately.
The defaults should work fine, however if you encounter slow enumeration, adjust the settings
according to your needs.
Additionally if it encounters anything like '421 Too many errors on this connection' it will
automatically and transparently reconnect and continue from where it left off.
positional arguments:
host IP or hostname to connect to.
port Port to connect to.
optional arguments:
-h, --help show this help message and exit
-v, --version Show version information,
-m mode, --mode mode Mode to enumerate SMTP users.
Supported modes: VRFY, EXPN, RCPT
Default: VRFY
-d addr, --domain addr
Domain to append to users to convert into email addresses.
Useful of you see this response: '550 A valid address is required'
Default: Nothing appended
-f addr, --from-mail addr
MAIL FROM email address. Only used in RCPT mode
Default: user@example.com
-u user, --user user Username to test.
-U file, --file file Newline separated wordlist of users to test.
-V, --verbose Show verbose output. Useful to adjust your timing and retry settings.
--timeout-init sec Timeout for initial communication (connect, banner and greeting).
Default: 25
--timeout-enum sec Timeout for user enumeration.
Default: 10
--retry-init int Number of retries for initial communication (connect, banner and greeting).
Default: 4
--retry-enum int Number of retries for user enumeration.
Default: 5
--reconnect int Number of reconnects during user enumeration after retries have exceeded.
Default: 3
VRFY mode (default)
The SMTP "VRFY" command allows you to verify whether a the system can deliver mail to a particular user.
Source: https://www.rapid7.com/db/vulnerabilities/smtp-general-vrfy
Successful VRFY mode output
$ smtp-user-enum -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
Start enumerating users with VRFY mode ...
[----] admin 550 5.1.1 admin... User unknown
[----] OutOfBox 550 5.1.1 OutOfBox... User unknown
[SUCC] root 250 2.1.5 root <root@mail.example.tld>
[SUCC] adm 250 2.1.5 <adm@mail.example.tld>
[----] avahi-autoipd 550 5.1.1 avahi-autoipd... User unknown
[----] backup 550 5.1.1 backup... User unknown
[TEST] bin ...
Failed VRFY mode output
In case the VRFY mode is not successful as shown below, you will need to try out a different mode.
$ smtp-user-enum -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
Start enumerating users with VRFY mode ...
[----] 4Dgifts 502 VRFY disallowed.
[----] EZsetup 502 VRFY disallowed.
[----] OutOfBox 502 VRFY disallowed.
[----] root 502 VRFY disallowed.
[----] adm 502 VRFY disallowed.
[----] admin 502 VRFY disallowed.
[----] administrator 502 VRFY disallowed.
[----] anon 502 VRFY disallowed.
EXPN mode
The SMTP "EXPN" command allows you to expand a mailing list or alias, to see where mail addressed to the alias actually goes. For example, many organizations alias postmaster to root, so that mail addressed to postmaster will get delivered to the system administrator. Issuing "EXPN postmaster" via SMTP would reveal that postmaster is aliased to root.
The "EXPN" command can be used by attackers to learn about valid usernames on the target system. On some SMTP servers, EXPN can be used to show the subscribers of a mailing list -- subscription lists are generally considered to be sensitive information.
Source: https://www.rapid7.com/db/vulnerabilities/smtp-general-expn
Successful EXPN mode output
$ smtp-user-enum -m EXPN -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
Start enumerating users with EXPN mode ...
[----] 4Dgifts 550 5.1.1 4Dgifts... User unknown
[----] EZsetup 550 5.1.1 EZsetup... User unknown
[----] OutOfBox 550 5.1.1 OutOfBox... User unknown
[SUCC] root 250 2.1.5 root <root@barry>
[SUCC] adm 250 2.1.5 root <root@barry>
[----] admin 550 5.1.1 admin... User unknown
[----] administrator 550 5.1.1 administrator... User unknown
[----] anon 550 5.1.1 anon... User unknown
[----] auditor 550 5.1.1 auditor... User unknown
Note: the right side shows to what mailbox the email will be forwarded for the alias.
Failed EXPN mode output
In case the EXPN mode is not successful as shown below, you will need to try out a different mode.
$ smtp-user-enum -m EXPN -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
Start enumerating users with EXPN mode ...
[----] adm 502 Unimplemented command.
[----] admin 502 Unimplemented command.
[----] administrator 502 Unimplemented command.
[----] anon 502 Unimplemented command.
[----] auditor 502 Unimplemented command.
[----] avahi 502 Unimplemented command.
[----] avahi-autoipd 502 Unimplemented command.
[----] bbs 502 Unimplemented command.
[----] bin 502 Unimplemented command.
RCPT mode
Successful RCPT mode output
$ smtp-user-enum -m RCPT -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
250 2.1.0 user@example.com... Sender ok
Start enumerating users with RCPT mode ...
[----] OutOfBox 550 5.1.1 OutOfBox... User unknown
[SUCC] root 250 2.1.5 root... Recipient ok
[SUCC] adm 250 2.1.5 adm... Recipient ok
[----] admin 550 5.1.1 admin... User unknown
[----] administrator 550 5.1.1 administrator... User unknown
[----] backup 550 5.1.1 backup... User unknown
[----] bbs 550 5.1.1 bbs... User unknown
[SUCC] bin 250 2.1.5 bin... Recipient ok
[----] checkfs 550 5.1.1 checkfs... User unknown
[----] checksys 550 5.1.1 checksys... User unknown
Troubleshooting EXPN mode
$ smtp-user-enum -m RCPT -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
250 2.1.0 user@example.com... Sender ok
Start enumerating users with RCPT mode ...
[----] 4Dgifts 550 A valid address is required.
[----] EZsetup 550 A valid address is required.
[----] OutOfBox 550 A valid address is required.
[----] root 550 A valid address is required.
[----] adm 550 A valid address is required.
By the above output you can see that pure usernames are not allowed to be specified,
this can be counteracted with the -d command, to append a domain to each username during enumeration:
$ smtp-user-enum -m RCPT -d 'example.com' -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
250 2.1.0 user@example.com... Sender ok
Start enumerating users with RCPT mode ...
[----] 4Dgifts 450 4.7.1 4Dgifts@example.com... Relaying temporarily denied. Cannot resolve PTR record for 10.11.0.226
[----] EZsetup 450 4.7.1 EZsetup@example.com... Relaying temporarily denied. Cannot resolve PTR record for 10.11.0.226
[----] OutOfBox 450 4.7.1 OutOfBox@example.com... Relaying temporarily denied. Cannot resolve PTR record for 10.11.0.226
[----] root 450 4.7.1 root@example.com... Relaying temporarily denied. Cannot resolve PTR record for 10.11.0.226
[----] adm 450 4.7.1 adm@example.com... Relaying temporarily denied. Cannot resolve PTR record for 10.11.0.226
Looks like the server is also hardened against relaying. To circumvent this, you could try to specify the server's hostname (cann be seen in the banner or greeting) or use 127.0.0.1 as the domain for users:
$ smtp-user-enum -m RCPT -d '127.0.0.1' -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
250 2.1.0 user@example.com... Sender ok
Start enumerating users with RCPT mode ...
[SUCC] 4Dgifts 250 2.1.5 4Dgifts@127.0.0.1... Recipient ok (will queue)
[SUCC] EZsetup 250 2.1.5 EZsetup@127.0.0.1... Recipient ok (will queue)
[SUCC] OutOfBox 250 2.1.5 OutOfBox@127.0.0.1... Recipient ok (will queue)
[SUCC] root 250 2.1.5 root@127.0.0.1... Recipient ok (will queue)
[SUCC] adm 250 2.1.5 adm@127.0.0.1... Recipient ok (will queue)
[SUCC] admin 250 2.1.5 admin@127.0.0.1... Recipient ok (will queue)
[SUCC] administrator 250 2.1.5 administrator@127.0.0.1... Recipient ok (will queue)
[SUCC] anon 250 2.1.5 anon@127.0.0.1... Recipient ok (will queue)
[SUCC] auditor 250 2.1.5 auditor@127.0.0.1... Recipient ok (will queue)
[SUCC] backup 250 2.1.5 backup@127.0.0.1... Recipient ok (will queue)
Looks like 127.0.0.1 as the user's domain leads to false positives, let's try the exact domain speified in the banner mail.example.tld:
$ smtp-user-enum -m RCPT -d '127.0.0.1' -U /usr/share/wordlists/metasploit/unix_users.txt mail.example.tld 25
Connecting to mail.example.tld 25 ...
220 mail.example.tld ESMTP Sendmail 8.12.8/8.12.8; Wed, 22 Jan 2020 19:33:07 +0200
250 mail.example.tld Hello [10.0.0.1], pleased to meet you
250 2.1.0 user@example.com... Sender ok
Start enumerating users with RCPT mode ...
[----] 4Dgifts 550 5.1.1 4Dgifts@mail.example.tld... User unknown
[----] EZsetup 550 5.1.1 EZsetup@mail.example.tld... User unknown
[----] OutOfBox 550 5.1.1 OutOfBox@mail.example.tld... User unknown
[SUCC] ROOT 250 2.1.5 ROOT@mail.example.tld... Recipient ok
[SUCC] adm 250 2.1.5 adm@mail.example.tld... Recipient ok
[----] admin 550 5.1.1 admin@mail.example.tld... User unknown
[----] administrator 550 5.1.1 administrator@mail.example.tld... User unknown
[----] anon 550 5.1.1 anon@mail.example.tld... User unknown
[----] auditor 550 5.1.1 auditor@mail.example.tld... User unknown
[----] avahi 550 5.1.1 avahi@mail.example.tld... User unknown
[----] avahi-autoipd 550 5.1.1 avahi-autoipd@mail.example.tld... User unknown
[----] backup 550 5.1.1 backup@mail.example.tld... User unknown
[----] bbs 550 5.1.1 bbs@mail.example.tld... User unknown
[SUCC] bin 250 2.1.5 bin@mail.example.tld... Recipient ok
[----] checkfs 550 5.1.1 checkfs@mail.example.tld... User unknown
Disclaimer
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.
License
Copyright (c) 2020 cytopia
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