I would like to block brute force attacks. I've added the following iptables rules and yet, the attacks are not blocked. I've tried similar rules with the same results. The attacks persist for about 8 or so minutes. Why is this not working?
Walt

iptables -N SSH_KILLER
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -j SSH_KILLER
iptables -A SSH_KILLER -m recent --set --name SSH
iptables -A SSH_KILLER -m recent --update --seconds 60 --hitcount 4 --name SSH -j DROP

seems ok to me
iptables => is the path correct?

what is the output of

SSH_KILLER tcp -- anywhere anywhere tcp dpt:22 state NEW
Chain SSH_KILLER (1 references)
all -- anywhere anywhere recent: SET name: SSH side: source
DROP all -- anywhere anywhere recent: UPDATE seconds: 60 hit_count: 4 name: SSH side: source


Thanks for looking at this...Walt

should work.
can you test from a remote computer?

I opened 6 putty windows and then attempted to login with 6 bogus id's. When the 6th one was entered, I received a connection refused. So, I guess that tells me it is working. But then, why do I see this in /var/log/messages?

BTW, I'm running openSUSE 10.3 on this machine.

Walt

Feb 2 21:19:06 spock sshd[4803]: Did not receive identification string from 210.82.89.139
Feb 2 21:22:49 spock sshd[4807]: User root from 210.82.89.139 not allowed because listed in DenyUsers
Feb 2 21:22:51 spock sshd[4813]: Invalid user usuario from 210.82.89.139
Feb 2 21:22:53 spock sshd[4818]: Invalid user irina from 210.82.89.139
Feb 2 21:22:56 spock sshd[4823]: Invalid user karin from 210.82.89.139
Feb 2 21:22:58 spock sshd[4828]: Invalid user cvs from 210.82.89.139
Feb 2 21:23:01 spock sshd[4833]: Invalid user cvsroot from 210.82.89.139
Feb 2 21:23:03 spock sshd[4838]: Invalid user paper from 210.82.89.139
Feb 2 21:23:06 spock sshd[4843]: Invalid user a from 210.82.89.139
Feb 2 21:23:08 spock sshd[4848]: Invalid user carter from 210.82.89.139
Feb 2 21:23:11 spock sshd[4853]: Invalid user paul from 210.82.89.139
Feb 2 21:23:13 spock sshd[4858]: Invalid user julie from 210.82.89.139
Feb 2 21:23:16 spock sshd[4863]: Invalid user tomato from 210.82.89.139
Feb 2 21:23:18 spock sshd[4868]: Invalid user dev from 210.82.89.139
Feb 2 21:23:21 spock sshd[4873]: Invalid user eric from 210.82.89.139
Feb 2 21:23:23 spock sshd[4878]: Invalid user morgan from 210.82.89.139
Feb 2 21:23:25 spock sshd[4883]: Invalid user jackson from 210.82.89.139

======================== SNIP =======================================

Feb 2 21:31:13 spock sshd[5810]: Invalid user ftpuser from 210.82.89.139
Feb 2 21:31:16 spock sshd[5815]: Invalid user master from 210.82.89.139
Feb 2 21:31:18 spock sshd[5820]: Invalid user oleg from 210.82.89.139
Feb 2 21:31:20 spock sshd[5825]: Invalid user eugene from 210.82.89.139
Feb 2 21:31:23 spock sshd[5830]: Invalid user max from 210.82.89.139
Feb 2 21:31:25 spock sshd[5835]: Invalid user java from 210.82.89.139
Feb 2 21:31:28 spock sshd[5840]: Invalid user rick from 210.82.89.139
Feb 2 21:31:30 spock sshd[5845]: Invalid user ruth from 210.82.89.139
Feb 2 21:31:33 spock sshd[5850]: Invalid user resin from 210.82.89.139
Feb 2 21:31:35 spock sshd[5855]: Invalid user delgado from 210.82.89.139
Feb 2 21:31:38 spock sshd[5860]: Invalid user sara from 210.82.89.139
Feb 2 21:31:40 spock sshd[5865]: Invalid user amanda from 210.82.89.139
Feb 2 21:31:42 spock sshd[5870]: Invalid user stan from 210.82.89.139
Feb 2 21:31:45 spock sshd[5875]: Invalid user denis from 210.82.89.139
Feb 2 21:31:47 spock sshd[5880]: Invalid user dennis from 210.82.89.139
Feb 2 21:31:50 spock sshd[5885]: Invalid user vivian from 210.82.89.139
Feb 2 21:31:52 spock sshd[5890]: Invalid user viviane from 210.82.89.139
Feb 2 21:31:55 spock sshd[5895]: Invalid user jacob from 210.82.89.139

iptables -N SSH_KILLER
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -j SSH_KILLER
iptables -A SSH_KILLER -m recent --set --name SSH
iptables -A SSH_KILLER -m recent --update --seconds 60 --hitcount 4 --name SSH -j LOG
iptables -A SSH_KILLER -m recent --update --seconds 60 --hitcount 4 --name SSH -j DROP

I'm no whiz at Netfilter, but I believe that's what you want.

I use a similar rule... and I know it does work.

Ymmv.

As a temporary thing i'd be inclined to:-
Just so to make sure at least temporarily unless they then start using another IP, that they will get no-where with their brute attack. Then is there a specific reason your creating a new chain, it will work just as well:-
Shouldn't be any problems with that, althought can't say i see an issue with what you've got either.

Ok,
I put the following rules in:
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 22 -m state --state NEW -m recent --update --seconds 360 --hitcount 3 --name SSHATTEMPTS --rsource -j DROP
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 22 -m state --state NEW -m recent --set --name SSHATTEMPTS --rsource

I thought that since it specifically pointed to eth0 that maybe that would work. Not so, I had to shut down the ssh daemon in the middle of an attack.

Will try the one form the last posting.
Walt

Feb 4 13:12:41 spock sshd[21647]: Invalid user admin65 from 221.139.3.36
Feb 4 13:12:43 spock sshd[21652]: Invalid user admin from 221.139.3.36
Feb 4 13:12:44 spock sshd[21657]: Invalid user admin from 221.139.3.36
Feb 4 13:12:46 spock sshd[21662]: Invalid user admin from 221.139.3.36
Feb 4 13:12:48 spock sshd[21667]: Invalid user admin from 221.139.3.36
Feb 4 13:12:49 spock sshd[21672]: Invalid user admin from 221.139.3.36
Feb 4 13:12:51 spock sshd[21677]: Invalid user admin from 221.139.3.36
Feb 4 13:12:52 spock sshd[21682]: Invalid user admin from 221.139.3.36
Feb 4 13:12:54 spock sshd[21687]: Invalid user admin from 221.139.3.36
Feb 4 13:12:55 spock sshd[21692]: Invalid user admin from 221.139.3.36
Feb 4 13:12:57 spock sshd[21697]: Invalid user admin from 221.139.3.36
Feb 4 13:12:59 spock sshd[21702]: Invalid user admin from 221.139.3.36
Feb 4 13:13:00 spock sshd[21707]: Invalid user admin from 221.139.3.36
Feb 4 13:13:02 spock sshd[21712]: Invalid user admin from 221.139.3.36
Feb 4 13:13:03 spock sshd[21717]: Invalid user admin from 221.139.3.36
Feb 4 13:13:05 spock sshd[21722]: Invalid user admin from 221.139.3.36
Feb 4 13:13:06 spock sshd[21727]: Invalid user admin from 221.139.3.36
Feb 4 13:13:08 spock sshd[21733]: Invalid user admin from 221.139.3.36
Feb 4 13:13:10 spock sshd[21739]: Invalid user admin from 221.139.3.36

Is there a way of deleting iptables rules without having to re-boot the system and add new replacement iptables rules?
Thanks,
Walt

Yes, just change the -A or -I which you used to a -D.

I'm curious how '--update --seconds N' works. Does it wake up every N seconds and check how many matches there have been since the last interval? If so, lowering the value of N should see improvement in how quickly an IP gets blocked.

One thing to remember... it's not number of attempts. It's number of connects. If your sshd lets them take 20 attempts per connect... it'll take 60 attempts before it gets rid of them.

I think the sshd_config options you want to look at is strictmode (should be yes), maxauthtries (your call, mines 2), and logingracetime (I use 30s).

or if you want to dump them all "iptables -F"

Thanks. No one is getting in, just seeing the attempts in the /var/log/messages log is annoying.
Walt