This blog is an update to my original post on ninja here

Briefly, ninja is a security tool that monitors your host (computer) for unauthorized root access (ie user privilege escalation) and, if discovered, logs and terminates (kills) the process.

From the Ninja Home Page

Ninja is a privilege escalation detection and prevention
system for GNU/Linux hosts. While running, it will monitor
process activity on the local host, and keep track of all
processes running as root. If a process is spawned with
UID or GID zero (root), ninja will log necessary informa-
tion about this process, and optionally kill the process
if it was spawned by an unauthorized user.

Since my original post the installation process and configuration has been modified and, although it is much easier to configure, ninja still requires post installation configuration.

Install ninja

$ sudo apt-get install ninja

Configure ninja

Most important, read the documentation. Most of the relevant information is in the configuration file,

These are the adjustments I made (for Ubuntu).

1. Add a “magic” group (only members of the magic group are allowed root access). In this blog I will call the group “ninja” , you may change the name if you wish. Take note of the group id (gid or number).

$ sudo addgroup ninja
 Adding group `ninja’ (GID 1002) …
 Done.

Add root, messagebus, and your administrative user(s) to the magic group.

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 $ sudo usermod -a -G ninja root
 $ sudo usermod -a -G ninja messagebus
 $ sudo usermod -a -G ninja bodhi

2. Make a log file, restrict access to both /etc/ninja and the log file to root.

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$ sudo touch /var/log/ninja.log
 $ sudo chmod o-rwx -R /etc/ninja/
 $ sudo chmod o-rwx /var/log/ninja.log

3. Using any editor, open /etc/ninja/ninja.conf

I encourage you to read the configuration file

$ sudo -e /etc/ninja/ninja.conf

Make the following changes match the number with the magic group id:

group = 1002

Test ninja:

$ sudo ninja start
bodhi@lucid:~$ sudo -i
 root@lucid:~# sudo -u nobody /bin/bash
 bash: /root/.bashrc: Permission denied
 nobody@lucid:~$ whoami
 nobody
 nobody@lucid:~$ sudo -i
 [sudo] password for nobody:
 Sorry, try again.

Exit the shell and/or close the terminal.

At this time ninja is configured only to log events.

Examining the log will show the event:

$ sudo cat /var/log/ninja.log
NEW ROOT PROCESS: bash[2319] ppid=2015 uid=0 gid=0
 - ppid uid=1000(bodhi) gid=1000 ppid=2013
 + bodhi is in magic group, all OK!
 NEW ROOT PROCESS: sudo[2338] ppid=2335 uid=0 gid=0
 - ppid uid=65534(nobody) gid=65534 ppid=2319
 + UNAUTHORIZED PROCESS DETECTED: sudo[2338] (parent: bash[2335])
 - nokill option set, no signals sent

Notice three things :

  1. bodhi was allowed to run sudo.
  2. ninja detected nobody was not authorized to run sudo.
  3. Last, ninja is configured with the “no kill” option, so did not take action.

Reboot

Before we complete our configuration of ninja, we need to test it. If ninja is configured incorrectly you may loose all root access !!!

Clear the log

$ sudo bash -c “> /var/log/ninja.log”

Reboot, test root (sudo) access and run your system for a few hours or days (your choice). Watch the ninja log. If there are events you will need to determine if you need to configure ninja further, either via adding users to the ninja group or white listing processes.

Add a user to the magic group

Use the graphical tool or command line to add users to the ninja group

$ sudo usermod -a -G ninja user_to_add

Whitelist a process

Edit /etc/ninja/whitelist

If you examine the file you will find there are already a few processes listed. If you need to add a process the syntax is

/path_to/program:group:user

where group/user is a group/user allowed to run the process

Enable ninja

Assuming you have configured ninja and you are not getting alerts in the ninja log, it is time to activate ninja.

Using any editor, open /etc/ninja/ninja.conf

$ sudo -e /etc/ninja/ninja.conf

Change these lines

 no_kill = no
 no_kill_ppid = no

restart ninja

$ sudo service ninja restart

Test ninja

bodhi@lucid:/usr/share/doc/ninja$ sudo -i
 root@lucid:~# sudo -u nobody /bin/bash
 bash: /root/.bashrc: Permission denied
 nobody@lucid:~$ sudo -i
 [sudo] password for nobody: Killed
 nobody@lucid:~$ Killed

Adding an automated alert

Using any editor, open /etc/ninja/ninja.conf and make some changes. The “problem” is that the external command now runs as the user who triggered ninja, so we need some modifications to the scripts (from my original post).

external_command = /etc/alert

YOU must write this script if you wish to use it.

Examples might include (save this script in /etc/alert ):

#!/bin/bash
 echo “Ninja attack” | mail -s “Alert” you@secret-service.com
 echo “Ninja attack” > /home/.ninja/ALERT

Note: I suggest putting the script OFF the normal path of users to prevent users from running the script.

Make the script executable:

$ sudo chmod 555 /etc/alert

Now add this to the end of .bashrc (at least for root and I would suggest adding it to your admin user as well):

#Ninja alert
 RED=’\e[0;31m'
 if [ -e /home/.ninja/ALERT ]; then
 clear
 echo ”
 echo -e “${RED}NINJA ATTACK”
 echo ”
 fi

If you use this script, to clear the alert use

$ sudo rm /home/.ninja/ALERT

Ninja in action

root@karmic# sudo -u nobody /bin/bash
 bash: /root/.bashrc: Permission denied
nobody@karmic$ whoami
 nobody
nobody@karmic$ sudo -i
 [sudo] password for nobody: Killed
 nobody@karmic$ Killed
 root@karmic#


Notice how ninja killed not only the sudo attempt, but the bash shell as well.

If you used my alert script and configured ~/.bashrc you will also see a warning when you log in or sudo -i to root. If you receive an alert, review your ninja log.

To clear the alert:

$ sudo rm /home/.ninja/ALERT

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