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How To Trap Bad Telnet Login Information (Username and Password)

Posted on 2007-11-21
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Last Modified: 2012-06-22
Hello,

We have users telnet (usually locally) into our servers (RedHat 8 and CentOS 4.5).

When we have a bad login attempt, I would like to be able to trap the bad username and password in a log file of some sort.

How can I do this?

Thanks in advance,

s1m0ne
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Question by:s1m0ne
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8 Comments
 
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Tintin earned 168 total points
ID: 20332095
Details will be in /var/log/secure as well as /var/log/messages
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by:WizRd-Linux
WizRd-Linux earned 166 total points
ID: 20332263
As far as I know there isn't a way to specifically split out the logs for specifically failed login attempts via telnet.

You can however edit /etc/syslog.conf and add a line similar to:

auth.notice        /var/log/auth.log

As I said, I don't know of a way to split it out so it will log notices and above for any programs that ask for a username and password, eg login, su, ftpd, sshd, telnetd.
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by:s1m0ne
ID: 20332268
Thanks, but how do I log the actual bad password in addition to the user?
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by:Tintin
ID: 20332295
You can't log the bad password without making custom changes to sit in middle of the login process.
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by:WizRd-Linux
ID: 20332331
Tintin is absolutely correct.  To log the bad password attempt you would have to modify the telnetd source to include the bad password in the log output then recompile it.
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Assisted Solution

by:omarfarid
omarfarid earned 166 total points
ID: 20332478
Hi,

How getting the bad passwords will help you? It is a security breach if you could capture users passwords.

It will be enough for you to know that certain account / accounts are failing to login which could till that either the end users need to be educated about how to login / enter password, or that some accounts are under risk of login attempts.

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