telnet?

Posted by Vivek Gite [Last updated: December 19, 2006]

If you use ssh as remote login service, use following command to find out all failed login attempts via ssh or telnet (don't use telnet):

Use grep command to find out authentication failure message from /var/log/messages file

Use awk and cut command to print IPs/hostname

Use sort command to sort them

Use uniq command to print total failed login attempts

1) Login as root user

2) Type following command at shell prompt:

# grep "authentication failure" /var/log/messages|awk '{ print $13 }' | cut -b7- | sort | uniq -c

Output:

 1 216.12.193.35
 2 DEVssh
 2 hack.baddomain.net
 ...
 ..

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Asim Says: December 27th, 2006 at 1:27 am
command does not work i’ve tried it in FC5
Ash Says: December 28th, 2006 at 6:18 pm
I got this among valid addresses:

1 ev/tty2
1 y2

Because sometimes log includes “1 more authentication failure” or “2 more authentication failures” instead of “authentication failure”.

I recommend not to rely on field # 13 and use some more sophisticated command with pattern matching like:

grep “authentication failure” /var/log/messages | sed -n -e “s/.*rhost=$[^ ]*$.*/\1/p” | sort | uniq -c

or similar. A.
Ash Says: December 29th, 2006 at 8:52 am
sed -n -e “/sshd/s/.*Invalid user $.*$ from $[^ ]*$.*/\2/p” /var/log/messages | sort | uniq -c

gives interesting results too. Thanks for nice “sort + uniq -c” hint.

Nice site, handy and useful articles… great. Ctrl+D.
DM Says: July 6th, 2008 at 10:28 pm
Is it good if there is no authentication failure message?

hehehehe

Just secured my server and it all stopped. I use to get a few per hour.

nice!

see google secure centos server.

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