ot: how to block persistent same invalid account, different IPs

[Jeff Abrahamson]

On 22/12/17 11:41, Voytek Eymont wrote:
> I've installed fail2ban, it seems to be working as it identified my failed
> test logins, BUT, my question is:
>
> what can I do when I see same invalid name trying to login to dovecot,
> different IP each time, how can I say block each IP as used by this name ?
> or it that a bad idea ?
>
> I can see two persistent attempts as so:
>
> I don't have such user 'ignacio' or 'julian'
>
> #  grep ignacio.munoz  /var/log/dovecot.log | wc
>      178    3436   35624
> #  grep ignacio.munoz  /var/log/dovecot.log | grep 'auth fail' | wc
>      178    3436   35624
>
> #  grep julian  /var/log/dovecot.log | wc
>      178    3432   34321
> #  grep julian  /var/log/dovecot.log | grep 'auth fail' | wc
>      178    3432   34321
>
>
> last 6 tries, sometimes have just : <ignacio.munoz>, sometimes, with tld
>
> Dec 22 17:00:33 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 8 secs): user=<ignacio.munoz at aaa.com>, method=PLAIN, rip=157.122.183.218,
> lip=163.47.110.6, TLS, session=<Z4JniOdgkgCderfa>
> Dec 22 17:01:06 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 7 secs): user=<ignacio.munoz>, method=PLAIN, rip=60.172.162.2,
> lip=163.47.110.6, TLS, session=<CsdriudgWAA8rKIC>
> Dec 22 18:58:26 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 10 secs): user=<ignacio.munoz at aaa.com>, method=PLAIN, rip=60.30.224.189,
> lip=163.47.110.6, TLS: Disconnected, session=<kvLWLelg0QA8HuC9>
> Dec 22 18:58:59 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 7 secs): user=<ignacio.munoz>, method=PLAIN, rip=220.164.2.138,
> lip=163.47.110.6, TLS: Disconnected, session=<T7T5L+lgRADcpAKK>
> Dec 22 19:30:28 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 6 secs): user=<ignacio.munoz at aaa.com>, method=PLAIN, rip=113.8.194.3,
> lip=163.47.110.6, TLS, session=<jfSgoOlgswBxCMID>
> Dec 22 19:31:09 imap-login: Info: Disconnected (auth failed, 1 attempts in
> 6 secs): user=<ignacio.munoz>, method=PLAIN, rip=58.210.119.226,
> lip=163.47.110.6, TLS, session=<moAVo+lg8gA60nfi>

fail2ban isn't really the right tool to fight massive DDOS attacks.  On 
the other hand, you don't seem to have that problem, so things work out 
maybe.

It's cleaner to know the future and ban the right things at the right 
times, but is there real harm from people trying bad logins from 
different IP's and you just wait for fail2ban to block each one?  Your 
log snippet covers 151 minutes, even fail2ban would normally have 
unjailed ip's after that much time.

-- 

Jeff Abrahamson
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+44 7920 594 255
https://www.p27.eu/jeff/

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