under some kind of attack

[mj]

Hi,

Thanks for the quick follow-ups! Much appreciated. After posting this, I 
immediately started working on fail2ban. And between my initial posting 
and now, fail2ban already blocked 114 IPs.

I have fail2ban with maxretry=1 and bantime=1800

However, it seems almost all IPs are different, and I don't think I can 
keep the above settings permanently.

Robert, your iptables suggestions are _very_ interesting! However, will 
they also work on imaps/993, because of the ssl?

Thanks for the quick replies!

MJ

On 07/18/2017 09:52 PM, Robert Schetterer wrote:
> Am 18.07.2017 um 21:44 schrieb mj:
>> Hi all,
>>
>> It seems we are under some kind of password guessing attack:
>>
>>> Jul 18 21:33:33 auth: Info:
>>> ldap(username1,103.6.223.61,<W7wLl5xUfABnBt89>): invalid credentials
>>> (given password: 1q2w3e4r5t)
>>> Jul 18 21:34:16 auth: Info:
>>> ldap(username1,221.4.61.180,<89WnmZxUrADdBD20>): invalid credentials
>>> (given password: 1q2w3e4r5t)
>>> Jul 18 21:36:13 auth: Info:
>>> ldap(username2,117.243.180.225,<ESWBoJxUdQB187Th>): invalid
>>> credentials (given password: 1q2w3e4r)
>>> Jul 18 21:36:50 auth: Info:
>>> ldap(username2,58.59.103.230,<j7fQopxUNgA6O2fm>): invalid credentials
>>> (given password: 1q2w3e4r)
>>> Jul 18 21:36:56 auth: Info:
>>> ldap(username4,58.215.13.154,<gtY5o5xUlQA61w2a>): invalid credentials
>>> (given password: 1q2w3e4r5t)
>>> Jul 18 21:37:18 auth: Info:
>>> ldap(username3,220.175.154.205,<lFxppJxUFADcr5rN>): invalid
>>> credentials (given password: 1q2w3e4r)
>>> Jul 18 21:37:25 auth: Info:
>>> ldap(username5,14.142.29.142,<40zopJxUSgAOjh2O>): invalid credentials
>>> (given password: 1q2w3e4r)
>>> Jul 18 21:37:27 auth: Info:
>>> ldap(username4,119.1.98.121,<JDQOpZxUCwB3AWJ5>): invalid credentials
>>> (given password: 1q2w3e4r5t)
>>> Jul 18 21:37:54 auth: Info:
>>> ldap(username3,218.76.156.11,<OMqtppxUMADaTJwL>): invalid credentials
>>> (given password: 1q2w3e4r)
>>
>> Different IPs, different usernames, but all (almost) the same password.
>>
>> Any idea what we can do about this??
>>
>> Any advice you could give us would be very much appreciated.
>>
>> MJ
> 
> perhaps this
> 
> https://wiki.dovecot.org/HowTo/Fail2Ban
> 
> 
> or you may adapt this
> 
> https://sys4.de/de/blog/2015/11/07/abwehr-des-botnets-pushdo-cutwail-ehlo-ylmf-pc-mit-iptables-string-recent-smtp/
> 
> https://sys4.de/de/blog/2014/03/27/fighting-smtp-auth-brute-force-attacks/
> 
> to pop3(s)/imap(s) and your needs
> 
> 
> 
> 
> Best Regards
> MfG Robert Schetterer
>