Tuesday, July 24, 2012

Linux admin tip : "Detecting root account logins"

Just wanted to share this tip that i found very simple, yet elegant. This tip is useful in a scenario where you would like to be notified/warned instantly (via email in this example) when someone logs in to the root account. This can be modified to monitor any account, but since root is a juicy target for hackers, we will use it for this example.

Sometimes the easy solution is the best and a lot of the time you just want a solution that gets the job done. There are multiple ways to accomplish this task but i like the simplicity of this one and ease of  its setup. Essentially, we will be adding a line of code to the .bash_profile file in root's home directory (/root/) that will simply construct and send an email to your email account, notifying you that someone has logged into the root account. The .bash_profile file is a script file that gets executed for a particular user when someone logs in via ssh or locally on a terminal. Simple enough right?

Lets start:

In a text editor, open up the .bash_profile hidden file found in root's home directory and add this to the bottom of the file.
who | mail -s "Someone logged in as root" your@email.com
Save the file then exit. To test this out, simply log out or reboot your computer. Of course for this to work, you would need an active internet connection, a mail client and an smtp server. In my case, for the smtp server, i had postfix installed. An alternative method to send the email will be essentially the same method i used in the swatch blog post using the sendemail program. This method would involve you leaving your hard coded password for your email account in the .bash_profile file which is rather in-secure but nonetheless, a method that will work.

It's well known that you should resist logging into the root account for performing day to day tasks. You should have an already created user with the relevant privileges to perform all necessary admin tasks. But lets say you frequently have to log into the root account for whatever reason. As you can imagine, when you log in as root legitimately, this will send an email each time to the specified account and hence adds more weight to your already obese inbox. Here is one solution.

Replace the code we wrote before in the .bash_profile file with this:
echo "who|mail -s 'Someone logged in as root' your@email.com" | at now + 1 min
Every time someone logs in as root, a new task is scheduled to be executed one minute from the time the user logged in. This means that everytime an authorized person logs in as root, a task will be scheduled to run within a min. A notification email will then be sent to your designated email address. However, if you the administrator needs to log in frequently, the one minute delay should give you enough time to remove the task from the schedule (at least on a system that logs in quickly; can increase the delay to 2 minutes or more if necessary). This is similar to your home security system where you would usually have to disarm the system before it goes off. Disarming our "root access notifier" is as simple as removing it from the scheduled tasks.

To remove the task:
root@desktop:~# atq // lists the scheduled tasks
1    tue Jul 24 11:36:00 2012 a root

root@desktop:~# atrm 1 //removes a specific task by its id number
 Or you can make a "Disarm" script with this: atq | cut -f1 | xargs atrm
that you can quickly execute when necessary.

Resources/Good Reading:
unixmen.com: Best practices to secure your server
at command

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