How to Block IP addresses that show up in /var/log/auth.log after so many attempts?

Posted on 2007-08-08
Medium Priority
Last Modified: 2010-04-22
Like most auth.log we have multiple failed attempts from various IP, usually trying to login as root. Is there any way to block a specific IP once it attempts to authenticate and fails more than three times?
Question by:douggoss
LVL 16

Accepted Solution

Blaz earned 1600 total points
ID: 19654117
It is possible to do, but it is simpler to limit login attempts from one IP in a timeframe:
iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW -m recent --set --name SSH
iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 8 --rttl --name SSH -j DROP

lines copied from:
LVL 19

Assisted Solution

by:http:// thevpn.guru
http:// thevpn.guru earned 400 total points
ID: 19654157
What you need is SNORT...it is an intrusion detection system for linux..you can setup the scenario asked for and other different scenarios through it.
LVL 16

Assisted Solution

Blaz earned 1600 total points
ID: 19654173
One method for locking IPs exceding login attempts is described in http://blinkeye.ch/mediawiki/index.php/SSH_Blocking

Also, if possible, you should limit from which IPs you can connect to the server via port 22.
LVL 32

Expert Comment

ID: 19654186
Wouldn't it be a good thing to leave it as it is now ? This is the record you have for future hack problems.

LVL 30

Expert Comment

by:Kerem ERSOY
ID: 19655027

I have some suggestions for you:
- First of all I'd suggest you to change your SSH port to a non-standard, if possible  greater then 1024  port. Becasue most of these attacks come from pepople having a scanner scanning well known ports.
- Then you might block password as authentication method and use certifiate authentication instead.

rsivanandan: using a live production system as a honey-pot :) Thanks but no thanks :)

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