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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