Re: [Full-disclosure] reduction of brute force login attempts via SSH through iptables --hashlimit

On 3/1/06, GroundZero Security <fd@xxxxxxx> wrote:
Well i had a few minutes time, so i updated the script a bit.

I did not use lastb though, as it wouldnt work (read the manpage.....)
Anyhow, maybe someone found it usefull so here is v.0.2 :

http://www.groundzero-security.com/code/bruteforce-block.sh

Any suggestions are welcome, insults and flames can be sent to /dev/null

-sk

GroundZero Security Research and Software Development
http://www.groundzero-security.com

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pub 1024D/69928CB8 2004-09-27 Stefan Klaas <sk@xxxxxxxxxxxxxxxxxxxxxxx>
sub 2048g/2A3C7800 2004-09-27

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Is this supposed to be like some 'My first attempt at scripting?

Please do not offer scripts like this as some people might believe it
is useful, or even secure. The same people that will run this in /tmp
with . in their path.

Please note that this entire script can ALL be done in 1, count them
1, awk command. (sed as well, but not worth it).

WTF is this?

lIP=`ifconfig|grep -1 eth0|grep inet|sed 's/inet addr://'|awk '{print $1}'`

If you are going to ATTEMPT to do something, at least use documented
options. It's ``grep -A1'' not ``grep -1''. Then a pipe into sed
THEN into awk?

lIP=`/sbin/ifconfig | awk '/^eth0/{getline; sub(".*:","",$2); print $2}'`
lIP=`/sbin/ifconfig | sed -ne '/^eth0/{n;s/^.*addr:\([^ \x09]*\).*/\1/;p}'`


cat /var/log/messages |grep "Failed password" >$fail
cat /var/log/messages |grep "Illegal user" >$fail2
cat /var/log/messages |grep "Invalid user" >$fail3
cat /var/log/messages |grep "Failed keyboard" >$fail4

Really? Really? yeah, /var/log/messages only has to be read ONE time
and the other files can be written to.

Which brings me to another point. Your use of static temp files in
the current working directory is just... my god. We will just assume
that 99% of all users do not use noclobber. You do know the
implemencations of this, right?

if [ "` cat $fail |grep "Failed password" |awk '{ print $15 }'`" == "" ];
then
cat $fail |grep "Failed password" |awk '{ print $11 }' >ips1
fi
if [ "` cat $fail2 |grep "Illegal user" |awk '{ print $14 }'`" == "" ];
then
cat $fail2 |grep "Illegal user" |awk '{ print $10 }' >ips2
fi
if [ "` cat $fail3 |grep "Invalid user" |awk '{ print $14 }'`" == "" ];
then
cat $fail3 |grep "Invalid user" |awk '{ print $10 }' >ips3
fi
if [ "` cat $fail4 |grep "Failed keyboard" |awk '{ print $17 }'`" == "" ];
then
cat $fail4 |grep "Failed keyboard" |awk '{ print $13 }' >ips4
fi


Ughh, reading those files enough? That makes no sense anyways, and
yet again we are clobbering static TEMPORARY files in the current
working directory.

echo "~ sorting out ip by ip"
for line in `cat ips1` # |read line
do
echo $line| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$' >>ip.$line
done
for line in `cat ips2` # |read line
do
echo $line| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$' >>ip.$line
done
for line in `cat ips3` # |read line
do
echo $line| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$' >>ip.$line
done
for line in `cat ips4` # |read line
do
echo $line| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$' >>ip.$line
done


See above. Not even going to comment on that again, let alone the
pattern match. Will throw something at that in a minute.


ls -la ip.*|awk '{ print $9 }' > ip.lst

That just makes no sense, yet again. Here is where you would use -1,
but with ls(documented and valid switch unlike in grep).


for line in `cat ip.lst`
do
if [ `wc -l $line |awk '{ print $1 }'` = '1' ];
then
# echo ""
# echo "not enough failed logins, probably no attack from: $line"
echo -n "*"
else if [ `wc -l $line |awk '{ print $1 }'` = '2' ];
then
# echo ""
# echo "not enough failed logins, probably no attack from: $line"
echo -n "*"
else if [ `wc -l $line |awk '{ print $1 }'` = '3' ];
then
# echo ""
# echo "not enough failed logins, probably no attack from: $line"
echo -n "*"
else if [ `wc -l $line |awk '{ print $1 }'` = '4' ];
then
# echo ""
# echo "not enough failed logins, probably no attack from: $line"
echo -n "*"
else
# generate list of the ip's to be blocked
# echo "* IP: $line will be blocked!"
echo -n "."
echo $line >>$blocklist
i=1;
fi
fi
fi
fi
done


You should have just done this way differently in the first place. And
Yippy! Another static temp file. $blocklist can be fun. This time no
clobbering so its even easier.

if [ $i != 0 ];
then
# edit blocklist (sometimes needs to be commented out or edited)
cat $blocklist |sed 's/ip.::ffff://' >g && mv g $blocklist

# cleanup
rm -f ip.* ips1 ips2 ips3 ips4 ip.lst $fail $fail2 $fail3 $fail4

for host in `cat $blocklist`
do
if ((${#host}>6)) && ((${#host}<16))
then
blk="`echo $host| grep
'^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$'`"
if [[ "$blk" != "$lIP" && "$blk" != "" ]];
then

echo " blocking IP: $blk" >> $log
echo "host: $host blk: $blk"
$fw -A INPUT -s $blk -j REJECT
fi
fi
done
cp $blocklist saved.blocklist
rm -f $blocklist

# left this in, in case you may not want to run this in background.
#
# echo "~ do you want to clean those entries from /var/log/messages ?"
# read -e answer

# if [ "$answer" == "y" ];
# then
echo "+ cleaning system logs.."
cat /var/log/messages |grep -v "llegal user" |grep -v "ailed
password" |grep -v "nvalid user"|grep -v "ailed keyboard" >m
echo "+ creating backup of old logfile.."
cp /var/log/messages msg.copy
echo "+ replacing logfile.."
cat m > /var/log/messages
rm -f m
# fi
else
echo "no attackers found."
fi
echo "finished."


Ohh, we are almost done! I liked symlinking m to /dev/urandom. It
made me feel good about myself.

grep | grep | grep | grep | grep | tee | grep | grep | cat | grep > /dev/stdout

What else do we have here?

$ export blocklist=blocklist fw=echo log=log
$ echo 0.0.0.0/0 >> $blocklist
$ for host in `cat $blocklist`
do
if ((${#host}>6)) && ((${#host}<16))
then
blk="`echo $host| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$'`"
if [[ "$blk" != "$lIP" && "$blk" != "" ]];
then

echo " blocking IP: $blk" >> $log
echo "host: $host blk: $blk"
$fw -A INPUT -s $blk -j REJECT
fi
fi
done
host: 0.0.0.0/0 blk: 0.0.0.0/0
-A INPUT -s 0.0.0.0/0 -j REJECT
$ cat log
blocking IP: 0.0.0.0/0

:( Your not blocking lIP did not matter, like it would anyways. You
made me sad. Notice your pattern match just LOVED accepting
0.0.0.0/0.

Hints:
bash
[ -e "$file" ]
[ -h "$file" ]
[ -n "$variable" ]
set -o
case/esac
IFS=.; set -- $host
${VAR//}
bc
mktemp
_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

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