Please whitelist cPanel in your adblocker so that you’re able to see our version release promotions, thanks!

The Community Forums

Interact with an entire community of cPanel & WHM users!

Closing smtp ports question

Discussion in 'E-mail Discussion' started by keat63, Feb 28, 2017.

Tags:
  1. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    I'm fed up of checking my logs daily to find brute force login attempts on emails, some times as many as 50 over night.
    So in CSF I closed ports 110,143,220,465,587,993,995 to all but my home country code.

    Either this is working to a point, or the hackers got bored and moved on.
    However, if it is working, then I'm still seeing a very small number, but I've no ideas why.

    Code:
    2017-02-28 02:41:29 SMTP connection from [xxx.xx.xxx.xxx]:50841 (TCP/IP connection count = 1)
2017-02-28 02:41:30 no host name found for IP address xxx.xx.xxx.xxx
2017-02-28 02:41:50 no host name found for IP address xxx.xx.xxx.xxx
2017-02-28 02:41:52 no host name found for IP address xxx.xx.xxx.xxx
2017-02-28 02:41:58 dovecot_plain authenticator failed for ([127.0.0.1]) [xxx.xx.xxx.xxx]:50841: 535 Incorrect authentication data (set_id=user)
2017-02-28 02:42:00 SMTP connection from ([127.0.0.1]) [xxx.xx.xxx.xxx]:50841 lost
2017-02-28 02:42:01 SMTP connection from [xxx.xx.xxx.xxx]:54329 (TCP/IP connection count = 1)
2017-02-28 02:42:01 no host name found for IP address xxx.xx.xxx.xxx
2017-02-28 02:45:06 SMTP command timeout on connection from [xxx.xx.xxx.xxx]:54329
    How would I find which port they might be using, so I can close this one too ??
     
    #1 keat63, Feb 28, 2017
  2. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    Hello,

    You may want to review your cPanel and Apache access logs for those IP addresses to see if they were accessing Webmail, or a script on a website, in order to send an email via SMTP.

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #2 cPanelMichael, Mar 3, 2017
  3. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    I don't see anything in cpanel or apache logs.

    Here's another, the IP being in Indonesia, so should be blocked.

    Code:
    2017-03-06 01:26:38 SMTP connection from [xxx.xxx.xxx.xxx]:37292 (TCP/IP connection count = 1)
2017-03-06 01:27:01 dovecot_plain authenticator failed for host112.subnet.xxxx.net.id (svrwebprodi112.zzzzzz.ac.id) [xxx.xxx.xxx.xxx]:37292: 535 Incorrect authentication data (set_id=user@mydomain.co.uk)
2017-03-06 01:27:01 SMTP connection from host112.subnet.xxxx.net.id (abcdef.ghijk.ac.id) [xxx.xxx.xxx.xxx]:37292 lost
2017-03-06 01:27:03 SMTP connection from [xxx.xxx.xxx.xxx]:40553 (TCP/IP connection count = 1)
2017-03-06 01:30:08 SMTP command timeout on connection from host112.subnet.xxxx.net.id [xxx.xxx.xxx.xxx]:40553
     
    #3 keat63, Mar 6, 2017
  4. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    is it possible that these login requests are coming via port 25
     
    #4 keat63, Mar 9, 2017
  5. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    Hello,

    Yes, it's possible if you have not applied the same firewall rules to port 25. If you decide to do so, ensure you leave the outgoing traffic over port 25 open to allow your mail server the ability to connect to remote mail servers over port 25.

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #5 cPanelMichael, Mar 13, 2017
  6. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    But if i close incoming port 25, then no mailserver will be able to establish a connection with me ??
     
    #6 keat63, Mar 15, 2017
  7. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    Right, you'd only receive email from servers that you whitelist. The following post explains how this works:

    change port 25

    It's likely a better option to simply manually block the remaining IP addresses you notice making failed login attempts.

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #7 cPanelMichael, Mar 15, 2017
  8. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    CSF is already taking care of this, however, it's annoying as I don't know how I'm still receiving failed smtp authentications when I already closed ports 110,143,220,465,587,993,995.
     
    #8 keat63, Mar 16, 2017
  9. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    It's likely happening over port 25 as you suggested. You may also find section 26 (Exim SMTP AUTH Restriction) on the CSF ReadMe helpful if you have not already enabled this SMTP authentication configuration:

    https://download.configserver.com/csf/readme.txt

    Beyond that, it's difficult to prevent all connection/authentication attempts without also blocking potentially legitimate requests.

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #9 cPanelMichael, Mar 16, 2017
  10. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    This is still onging.


    2017-10-09 16:12:16 SMTP connection from [xxx.xxx.xxx.xx]:51334 (TCP/IP connection count = 1)
    2017-10-09 16:12:21 dovecot_plain authenticator failed for (127.0.0.1) [xxx.xxx.xxx.xx]:51334: 535 Incorrect authentication data (set_id=admin@domain.com)
    2017-10-09 16:12:27 SSL_write: (from (127.0.0.1) [xxx.xxx.xxx.xx]:51334) syscall: Broken pipe
    2017-10-09 16:12:27 dovecot_login authenticator failed for (127.0.0.1) [xxx.xxx.xxx.xx]:51334: 535 Incorrect authentication data (set_id=AB\023)
    2017-10-09 16:12:27 SMTP connection from (127.0.0.1) [xxx.xxx.xxx.xx]:51334 lost

    I found this in the message log for a similar login attempt.

    [6883341.422495] Firewall: *TCP_IN Blocked* IN=eth0 OUT= MAC=00:19:99:78:1e:4f:00:18:74:67:50:00:08:00 SRC=xxx.xxx.xxx.xx DST=xxx.xxx.xxx.xx LEN=60 TOS=0x00 PREC=0x00 TTL=53 ID=14778 DF PROTO=TCP SPT=42475 DPT=587 WINDOW=5808 RES=0x00 SYN URGP=0

    which would indicate port 587, but port 587 is closed in CSF
     
    #10 keat63, Oct 10, 2017
    Last edited by a moderator: Oct 10, 2017
  11. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    Hello,

    Are there any corresponding entries in /usr/local/cpanel/logs/access_log around the same date/time that would suggest these entries stem from Webmail access?

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #11 cPanelMichael, Oct 10, 2017
  12. keat63

    keat63 Well-Known Member

    Joined:
    Nov 20, 2014
    Messages:
    1,030
    Likes Received:
    47
    Trophy Points:
    28
    cPanel Access Level:
    Root Administrator
    I don't see anything in access.log around this time other than a few localhost (127) entries.
     
    #12 keat63, Oct 11, 2017
  13. cPanelMichael

    cPanelMichael Technical Support Community Manager
    Staff Member

    Joined:
    Apr 11, 2011
    Messages:
    45,216
    Likes Received:
    1,937
    Trophy Points:
    363
    cPanel Access Level:
    Root Administrator
    Twitter:
    This message output shows the connection was blocked by the firewall. As far as the other log entries, are you sure it's not due to traffic over port 25, as discussed earlier in the thread?

    Thank you.
     
    Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
    #13 cPanelMichael, Oct 11, 2017
(You must log in or sign up to post here.)
Loading...
Similar Threads - Closing smtp ports
  1. Rafael Gomes

    SMTP connection from - lost while reading message data

    Rafael Gomes, Nov 16, 2018 at 6:18 AM, in forum: E-mail Discussion
    Replies:
    1
    Views:
    39
    cPanelMichael
    Nov 16, 2018 at 12:31 PM
  2. sparek-3

    SMTP Connection - lost while reading message data

    sparek-3, Nov 8, 2018, in forum: E-mail Discussion
    Replies:
    10
    Views:
    172
    Al Gilson
    Nov 15, 2018 at 3:01 PM
  3. dorkstanner

    Require localhost SMTP auth

    dorkstanner, Oct 24, 2018, in forum: E-mail Discussion
    Replies:
    2
    Views:
    96
    cPanelMichael
    Oct 26, 2018
  4. Mike1

    SMTP error from remote mail server after RCPT TO: 451

    Mike1, Oct 23, 2018, in forum: E-mail Discussion
    Replies:
    3
    Views:
    176
    cPanelLauren
    Oct 25, 2018
  5. wofflin

    Outlook 2013 can't auth smtp

    wofflin, Oct 16, 2018, in forum: E-mail Discussion
    Replies:
    1
    Views:
    108
    cPanelLauren
    Oct 17, 2018

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Accept Learn More...
    Dismiss Notice