On 08/01/2022 14:26, dc...@dvl.werbittewas.de wrote:
Am 08.01.22 um 05:27 schrieb Dave McGuire:
trying to mess with other peoples' stuff. I run fail2ban to catch those
log entries and block the source IP address for a month on the first
failed login. At any one time I have between 12,000 and 15,000
well, I don't know how _your_ users are connected to the internet, but
in germany most people has at least daily changing IPs out of larger
pools (when connected via xDSL) or even sometimes shares ip-addresses
with others (when connected via tv-cable or mobile - having a private
network-address, which is natted), so it's possible to get/use an IP,
which was used before by some script-kiddies...
so everyone, who's blocking such requests for more than some
minutes/hours should be aware of maybe blocking legitimate user-logins...
btw.: setting up a new mail-client and making any mistake by reading it
from old install or writing it into new install also leads to a
months-blocking with above restrictive handling...
(any may drive this user mad)
so anyone, who has no experience with blocking should be really careful
with it.
d.
yes, blocking on the first wrong password sounds like overkill. But it
does depend on user base. For a small mail server with few known users
it could be workable.
But even on small servers I'd recommend blocking for a small time (like
up to an hour) after a small number of failures (example 3). Then if
this pattern repeats (for example 3 times) within a longer period (for
example up to a day), blocking for a longer period (example 1 week)
using the recidive jail.
Mileage will vary depending on user base and number of support requests
generated.
The point about fail2ban is that it slows down attackers stopping
infinite and fast repeating attacks from the same ip. That should be in
combination with a good password policy which reduces the probability of
any single attack guessing the password. It doesn't necessarily have to
zero out attacks. As Dave has experimented, to bypass fail2ban all the
attacker has to do is use a different ip. 10-15K blocks in place at any
time seem very high compared to the few attacks I see.
I'd hazard a guess that the restrictive fail2ban policy is causing the
attacker(s) to try immediately from a new ip and isn't generating a
great deal more security than a slightly less restrictive policy which
lures the attacker into trying a few times more from the same ip with
longer intervals between the attempts.
John
