linux-kernel - Re: kernel.org status: hints on how to check your machine for intrusion

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Date:	Sat, 01 Oct 2011 23:06:57 +0100
From:	"Frank A. Kingswood" <frank@...gswood-consulting.co.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Willy Tarreau <w@....eu>, Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: kernel.org status: hints on how to check your machine for intrusion

On 01/10/11 19:06, Steven Rostedt wrote:
> On Sat, Oct 01, 2011 at 09:35:33AM +0200, Willy Tarreau wrote:
>>
> For my machine that is connected to the outside world, I have a script
> that runs every night that checks for attacks. As bots constantly look
> for port 22 and 80, they find my machine without issue. When my script
> detects a bunch of ssh login attempts that fail, it will add that ip
> address to the iptables DROP chain:
>
> # iptables -L -n | grep DROP | wc -l
> 2656
>
> I've picked up quite a few ;)
>
> This script only runs and scans once at night. Probably better to have
> it run more often.

Limiting SSH accesses to a few a minute (failed or not) is useful to 
block many password guess attacks. I set up mine a long time ago 
following this article using "recent" matches in iptables:

http://www.debian-administration.org/articles/187

You'll want to set the same rules for ipv6.

This won't stop low frequency and distributed attacks, and sometimes but 
extremely rarely I find myself connecting more quickly than the rate limit.

Setting "PasswordAuthentication no" in your sshd_config is good too.

Regards,

Frank

-- 
------------------------------------------------------------------------
Frank A. Kingswood                      frank@...gswood-consulting.co.uk
Cambridge, United Kingdom                               +44-870-095 0000
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