under some kind of attack

[Robert Schetterer]

Am 18.07.2017 um 22:15 schrieb 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?

i guess not, but typical bots arent using ssl, check it

however fail2ban sometimes is to slow
but as an alternative you may create a filter out of syslog to directly
feed in iptables recent, here is an example with smtp

https://sys4.de/de/blog/2012/12/28/botnets-mit-rsyslog-und-iptables-recent-modul-abwehren/



> 
> 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
>>



Best Regards
MfG Robert Schetterer

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