under another kind of attack

[Robert Schetterer]

Am 25.07.2017 um 16:37 schrieb Olaf Hopp:
> Hi folks,
> 
> "somehow" similar to the thread "under some kind oof attack" started by
> "MJ":
> 
> I have dovecot shielded by fail2ban which works fine.
> But since a few days I see many many IPs per day knocking on
> my doors with wron password and/or users. But the rate at which they are
> knocking
> is very very low. So fail2ban will never catch them.
> 
> For example one IP:
> 
> Jul 25 14:03:17 irams1 dovecot: auth-worker(2212):
> pam(eurodisc,101.231.247.210,<gAulHSNVsNZl5/fS>): unknown user
> Jul 25 15:16:36 irams1 dovecot: auth-worker(11047):
> pam(gergei,101.231.247.210,<dPzYIyRVtOpl5/fS>): pam_authenticate()
> failed: Authentication failure (password mismatch?)
> Jul 25 16:08:51 irams1 dovecot: auth-worker(3379):
> pam(icpe,101.231.247.210,<Ws6t3iRVkOhl5/fS>): unknown user
> Jul 25 16:10:47 irams1 dovecot: auth-worker(4250):
> pam(endsulei,101.231.247.210,<dceL5SRVGZVl5/fS>): unknown user
> 
> Note the timestamps.
> If I look the other way round (tries to one account) I'll get
> 
> Jul 25 01:30:48 irams1 dovecot: auth-worker(11276):
> pam(endsulei,60.166.12.117,<slp6mhhViI48pgx1>): unknown user
> Jul 25 01:31:26 irams1 dovecot: auth-worker(11276):
> pam(endsulei,222.243.211.200,<s0+6nBhVabHe89PI>): unknown user
> Jul 25 13:29:22 irams1 dovecot: auth-worker(4745):
> pam(endsulei,60.2.50.114,<4elhpCJVtcw8AjJy>): unknown user
> Jul 25 13:30:27 irams1 dovecot: auth-worker(4747):
> pam(endsulei,222.84.118.83,<kaE1qCJVn7neVHZT>): unknown user
> Jul 25 16:10:47 irams1 dovecot: auth-worker(4250):
> pam(endsulei,101.231.247.210,<dceL5SRVGZVl5/fS>): unknown user
> Jul 25 16:11:45 irams1 dovecot: auth-worker(5933):
> pam(endsulei,206.214.0.120,<R5H56CRVdJfO1gB4>): unknown user
> 
> Also note the timestamps!
> 
> And I see many many distinct IPs per day (a few hundred) trying many
> many existing and non-existings accounts.
> As you see in the timestamps in my examples, this can not be handled by
> fail2ban without affecting
> regular users with typos.
> Is anybody observing something similar ?


all the time ,since years, in my case its
always schema user xyz.abc
in my case all username without @ could be dropped at once
a regex deny should be fine, but i havent implemented/thinked of  it cause
it comming in small waves and mostly fail2ban stops it soon



> Anybody an idea against this ?
> Many of these observed IPs are chinese mobile IPs, if this matters. But
> we have also chinese students and
> researchers all abroad.
> 
> 
> Regards,
> Olaf
> 



Best Regards
MfG Robert Schetterer

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