1 Topic by pbf343

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Topic: connections & fail2ban vs spam

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CentOS, MySQL, iRedAdmin-Pro

Seeing connections similar to the below scenario from various IPs in the /var/log/maillog.  I'm wondering what they indicate and/or if associated with an account breach? 

May 23 00:08:21 mail02 postfix/smtpd[11381]: connect from unknown[132.245.70.197]
May 23 00:08:21 mail02 postfix/smtpd[11381]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 00:08:21 mail02 postfix/smtpd[11381]: disconnect from unknown[132.245.70.197]
May 23 01:20:36 mail02 postfix/smtpd[15731]: connect from unknown[132.245.70.197]
May 23 01:20:36 mail02 postfix/smtpd[15731]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 01:20:37 mail02 postfix/smtpd[15731]: disconnect from unknown[132.245.70.197]
May 23 02:20:43 mail02 postfix/smtpd[18888]: connect from unknown[132.245.70.197]
May 23 02:20:44 mail02 postfix/smtpd[18888]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 02:20:44 mail02 postfix/smtpd[18888]: disconnect from unknown[132.245.70.197]
May 23 03:20:48 mail02 postfix/smtpd[27549]: connect from unknown[132.245.70.197]
May 23 03:20:48 mail02 postfix/smtpd[27549]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 03:20:49 mail02 postfix/smtpd[27549]: disconnect from unknown[132.245.70.197]
May 23 04:20:56 mail02 postfix/smtpd[31188]: connect from unknown[132.245.70.197]
May 23 04:20:56 mail02 postfix/smtpd[31188]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 04:20:56 mail02 postfix/smtpd[31188]: disconnect from unknown[132.245.70.197]
May 23 05:27:32 mail02 postfix/smtpd[2829]: connect from unknown[132.245.70.197]
May 23 05:27:33 mail02 postfix/smtpd[2829]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 05:27:33 mail02 postfix/smtpd[2829]: disconnect from unknown[132.245.70.197]
May 23 06:28:24 mail02 postfix/smtpd[6565]: connect from unknown[132.245.70.197]
May 23 06:28:24 mail02 postfix/smtpd[6565]: Anonymous TLS connection established from unknown[132.245.70.197]: TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)
May 23 06:28:24 mail02 postfix/smtpd[6565]: disconnect from unknown[132.245.70.197]

Shouldn't fail2ban stop these?
One IP had over 8000 connections.

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2 Reply by ZhangHuangbin

  • ZhangHuangbin
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Re: connections & fail2ban vs spam

This is normal smtp connection with TLS support. But connect and disconnect immediately is not usual.

3 Reply by pbf343 (edited by pbf343 2017-05-23 23:19:15)

  • pbf343
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Re: connections & fail2ban vs spam

ZhangHuangbin wrote:

This is normal smtp connection with TLS support. But connect and disconnect immediately is not usual.

Yes.  However, over 8400 connections within 24 hours on a system this size from one IP makes me highly suspicious.  How, or what, can be done to determine further information on these connections like a target address(es), breach in user account(s), etc.?

Thank you.

4 Reply by ZhangHuangbin

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Re: connections & fail2ban vs spam

Unfortunately, we don't have such tool to detect this situation and block the IP automatically.

5 Reply by Waschl

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Re: connections & fail2ban vs spam

You can add the IP to /etc/postfix/postscreen_access.cidr. That blocks the client but it has to be done manually.

6 Reply by raz

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Re: connections & fail2ban vs spam

i think you can add this line "disconnect from unknown[<HOST>\]" as failregex in /etc/fail2ban/filter.d/postfix.iredmail.conf.

but you will need to customize it a little.

Raz

7 Reply by ZhangHuangbin

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Re: connections & fail2ban vs spam

raz wrote:

i think you can add this line "disconnect from unknown[<HOST>\]" as failregex in /etc/fail2ban/filter.d/postfix.iredmail.conf.

All clients with invalid or missed DNS record will match this rule. I don't think this is what you really want.