Wednesday, March 29, 2017

More Postfix Success

I've been delving into why I don't see Postfix bans in my logs.  I think it has to do with the filters that came with my install of Fail2ban...they don't work for Ubuntu.

I looked at my logs and saw a ton of bruteforce attempts against the SMTP service, so I know for a fact that Fail2ban should be blocking these attempts.

I found this page and wanted to test to see if it's filter's regex would work on my server, so created the filter based on what was on that page then edited my jail.local file.  I then restarted Fail2ban but also wanted to see if the filter works, so I ran this:


root@linode:/var/log# fail2ban-regex /var/log/mail.log /etc/fail2ban/filter.d/postfix-auth.conf

Running tests

Use   failregex filter file : postfix-auth, basedir: /etc/fail2ban
Use         log file : /var/log/mail.log
Use         encoding : UTF-8


Failregex: 1526 total
|-  #) [# of hits] regular expression
|   1) [1526] ^\s*(<[^.]+\.[^.]+>)?\s*(?:\S+ )?(?:kernel: \[ *\d+\.\d+\] )?(?:@vserver_\S+ )?(?:(?:\[\d+\])?:\s+[\[\(]?postfix/smtpd(?:\(\S+\))?[\]\)]?:?|[\[\(]?postfix/smtpd(?:\(\S+\))?[\]\)]?:?(?:\[\d+\])?:?)?\s(?:\[ID \d+ \S+\])?\s*lost connection after .*\[\]$

Ignoreregex: 0 total

Date template hits:
|- [# of hits] date format
|  [10563] (?:DAY )?MON Day 24hour:Minute:Second(?:\.Microseconds)?(?: Year)?

Lines: 10563 lines, 0 ignored, 1526 matched, 9037 missed [processed in 0.88 sec]
Missed line(s): too many to print.  Use --print-all-missed to print all 9037 lines


This time I had matches.  The last few days of me trying this with other filters or editing the canned filters netted me nothing.

Then I checked my server's fail2ban logs:


 2017-03-29 21:53:56,987 fail2ban.filter         [12346]: INFO    [postfix-auth] Found
2017-03-29 21:53:57,037 fail2ban.filter         [12346]: INFO    [postfix-auth] Found
2017-03-29 21:53:57,971 fail2ban.actions        [12346]: NOTICE  [postfix-auth] Ban
2017-03-29 22:03:56,413 fail2ban.filter         [12346]: INFO    [postfix-auth] Found
2017-03-29 22:07:03,231 fail2ban.filter         [12346]: INFO    [postfix-auth] Found
2017-03-29 22:12:31,667 fail2ban.filter         [12346]: INFO    [postfix-auth] Found


So it is working.

Why do I want use Fail2ban to block bad traffic going to my SMTP service?  Well, when I checked one of those IPs above, just to see how noisy it was in the log files, this is what I saw:

root@linode:/var/log# grep mail.log | grep connect | wc -l
root@linode:/var/log# grep mail.log.1 | grep connect | wc -l
root@linode:/var/log# zgrep mail.log.*.gz | grep connect | wc -l

A grand total of 14,005 connection attempts between the 13th and 29th of March.  The filter is configured to block if more than 2 attempts occur in a 5 minute span of time, so it should now block most of these.  I'll watch to see if that filter's parameters work sufficiently, but at least I've a working filter now!
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