under another kind of attack

[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 ?
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

-- 
Karlsruher Institut für Technologie (KIT)
ATIS - Abt. Technische Infrastruktur, Fakultät für Informatik

Dipl.-Geophys. Olaf Hopp
- Leitung IT-Dienste -

Am Fasanengarten 5, Gebäude 50.34, Raum 009
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Fax: +49 721 608-46699
E-Mail: Olaf.Hopp at kit.edu
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