full-disclosure - Re: targetted SSH bruteforce attacks

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Date: Thu, 17 Jun 2010 16:21:45 +0200
From: Samuel Martín Moro <faust64@...il.com>
To: Gary Baribault <gary@...ibault.net>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: targetted SSH bruteforce attacks

I also don't want to change my ssh port, nor restrict incoming IPs, ... and
I use keys only to log in without entering password.
So you're not alone.
I had my IP changed several times, my servers are only hosting personal
data.
But I'm still seeing bruteforce attemps in my logs.

Here's something I use on my servers.
In cron, every 5-10 minutes, that should do it.
Of course, if you're running *BSD, pf is way more interesting to do that.


---

#!/bin/sh

AUTH=/var/log/auth.log
BKLST=/var/log/blacklist.log
HOSTS=/etc/hosts
DHOSTS=/etc/hosts.deny
LOCAL_IP=_your_ip_

cat $AUTH | egrep -i "(failed|illegal|invalid)" | awk -F "from" '{ print $2
}' | awk '{ print $1 }' | sort -u >$BKLST

for i in `cat $BKLST`
do
    test `cat $AUTH | egrep -i "(failed|illegal|invalid)" | grep $i | wc
-l` -ge 3 || continue
    test "`echo $i | grep $LOCAL_IP`" && continue
    test "`cat $HOSTS | grep $i`" && continue
    test "`cat $DHOSTS | grep $i`" && continue
    echo "ALL : $i  # matched on `date`" >>$DHOSTS
done

---

Samuel Martín Moro
{EPITECH.} tek4
CamTrace S.A.S

"Nobody wants to say how this works.
 Maybe nobody knows ..."
                     Xorg.conf(5)


On Thu, Jun 17, 2010 at 1:48 PM, Gary Baribault <gary@...ibault.net> wrote:

> Hello list,
>
>    I have a strange situation and would like information from the
> list members. I have three Linux boxes exposed to the Internet. Two of
> them are on cable modems, and both have two services that are publicly
> available. In both cases, I have SSH and named running and available
> to the public. Before you folks say it, yes I run SSH on TCP/22 and no
> I don't want to move it to another port, and no I don't want to
> restrict it to certain source IPs.
>
>    Both of these systems are within one /21 and get attacked
> regularly. I run Denyhosts on them, and update the central server once
> an hour with attacking IPs, and obviously also download the public
> hosts.deny list.
>
>    These machines get hit regularly, so often that I don't really
> care, it's fun to make the script kiddies waste their time! But in
> this instance, only my home box is being attacked... someone is
> burning a lot of cycles and hosts to do a distributed dictionary
> attack on my one box! The named daemon is non recursive, properly
> configured, up to date and not being attacked.
>
>    Is anyone else seeing this type of attack? Or is someone really
> targeting MY box?
>
> Thanks
>
>
> Gary Baribault
> Courriel: gary@...ibault.net
> GPG Key: 0x685430d1
> Signature: 9E4D 1B7C CB9F 9239 11D9 71C3 6C35 C6B7 6854 30D1
>
> _______________________________________________
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