full-disclosure - SSH Bruteforce blocking script

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Message-ID: <A54C844ED592544A8AA8EF69AAB04018034886@sbswin001>
Date: Fri Sep  2 09:36:53 2005
From: mike.benjamin at clarinet.com.au (Michael L Benjamin)
Subject: SSH Bruteforce blocking script

Hmm even that is no good.

I would also suggest chown root.root ${TMP_FILE} in there too after chmod. In case a user
is attempting to insert a change during the tiny window in which the file is about to be clobbered.

Sorry for wasting bandwidth but for the sake of correctness, I think it's the right thing to do.

Cheers, Mike. 

-----Original Message-----
From: full-disclosure-bounces@...ts.grok.org.uk [mailto:full-disclosure-bounces@...ts.grok.org.uk] On Behalf Of Michael L Benjamin
Sent: Friday, September 02, 2005 04:31 PM
To: full-disclosure@...ts.grok.org.uk
Subject: RE: [Full-disclosure] SSH Bruteforce blocking script

Ok, well spotted. Something for me to fix there.

Here you go, add these lines to the script just after the touch:

chmod 700 ${TMP_FILE}
> ${TMP_FILE}

My apologies, that is a no-no and something I should have spotted.

I originally thought about doing this with arrays in memory. I might go back to that later.

Thanks for your input.

Cheers, Mike.

-----Original Message-----
From: full-disclosure-bounces@...ts.grok.org.uk [mailto:full-disclosure-bounces@...ts.grok.org.uk] On Behalf Of Alejandro Barrera
Sent: Friday, September 02, 2005 04:04 PM
To: full-disclosure@...ts.grok.org.uk
Subject: Re: [Full-disclosure] SSH Bruteforce blocking script

Well, we apreciate your script although I would preffer to stay with my nice bruteforcing attempts than to create an insecure temporary file bug:

ergosum@...rta:~$ cat test.sh
#!/bin/sh

SCRIPT_NAME=$(basename $0)
TMP_FILE="/tmp/${SCRIPT_NAME}.$$"

touch ${TMP_FILE}
echo "pwn3d" > ${TMP_FILE}
exit
ergosum@...rta:~$ cat data
pr0n g0ld collection: ....

ergosum@...rta:~$ ln -s /home/ergosum/data /tmp/test.sh.18359 ergosum@...rta:~$ ln -s /home/ergosum/data /tmp/test.sh.18361 ergosum@...rta:~$ ln -s /home/ergosum/data /tmp/test.sh.18362 ergosum@...rta:~$ ./test.sh ergosum@...rta:~$ cat data pwn3d

> #!/bin/ksh
> #
> # ssh_brute_blocker
> #
> # 05/07/2004 15:05 - Michael L. Benjamin #

> SCRIPT_NAME=$(basename $0)
> LOG_FILE="/var/log/secure"
> DENY_FILE="/etc/hosts.deny"
> TMP_FILE="/tmp/${SCRIPT_NAME}.$$"
> INBOUND_IP=""
> INLINE=""
> GUESS_COUNT=0
> PERMIT_GUESS=4

> touch ${TMP_FILE}

> while :
> do

> tail -10000 ${LOG_FILE} | grep "Failed password for illegal user" | 
> awk -F"from" {'print $2'} | awk {'print $1'} | uniq > ${TMP_FILE}

--
Alejandro Barrera Garc?a-Orea
R&D Engineer
c/ Alcala 268 28027 Madrid
Office: +34 91 326 66 11
Fax: +34 91 326 66 11
e-mail: abarrera@...n-gate.net

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