How to Install and Configure Tripwire IDS on Ubuntu 16.04

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By Hitesh Jethva, Alibaba Cloud Tech Share Author. Tech Share is Alibaba Cloud's incentive program to encourage the sharing of technical knowledge and best practices within the cloud community.

Tripwire is a free, open source host-based Intrusion Detection System (IDS) that can be used to detect if unauthorized filesystem changes occurred over time. Tripwire continuously monitor computer's filesystem, when an expected change occurs, such as upgrading a package, the baseline database can be updated to the new known-good state. Tripwire works by collecting detail information of your filesystem and stores this information to reference and validate the current state of the system. If changes are found between the known-good state and the current state, Tripwire will send an alert to you. The baseline and check behavior are controlled by a policy file, which specifies which files or directories to monitor, and which attributes to monitor on them, such as hashes, file permissions, and ownership. Tripwire allows the system admin to know immediately what was compromised and fix it.

In this tutorial, we will be installing and using Tripwire IDS on an Alibaba Cloud Elastic Compute Service (ECS) with Ubuntu 16.04.

Prerequisites

A fresh Alibaba Cloud Ubuntu 16.04 instance.
A static IP address is configured.
A root password is set up to your instance.

Launch Alibaba Cloud ECS Instance

First, log in to your Alibaba Cloud ECS Console. Create a new ECS instance, choosing Ubuntu 16.04 as the operating system with at least 2GB RAM. Connect to your ECS instance and log in as the root user.

Once you are logged into your Ubuntu 16.04 instance, run the following command to update your base system with the latest available packages.

apt-get update -y

Install Tripwire

By default, Tripwire is available in the Ubuntu 16.04 default repository. You can install it by just running the following command:

apt-get install tripwire -y

During the installation, you'll be prompted with several messages with various options.

First, you will be asked to provide SMTP configuration. Select Internet Site and click OK to continue the installation.

Here, you will be asked for Tripwire configuration agreement. Click OK. You will be redirected to site-key creation page.

Click Yes to create a site key passphrase.

Click Yes to rebuild the Tripwire configuration.

Click Yes to rebuild the Tripwire policy file. You should see the following page:

Provide your site-key passphrase and click Ok. You should see the following page:

Provide your local key passphrase and click Ok. Once the installation has been completed. You should see the following page:

Configure Tripwire Policy

Before starting, you will need to initialize the Tripwire database system. You can do this by running the following command:

tripwire --init

You should see the following output:

Please enter your local passphrase: 
Parsing policy file: /etc/tripwire/tw.pol
Generating the database...
*** Processing Unix File System ***
### Warning: File system error.
### Filename: /var/lib/tripwire/mail.example.com.twd
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /etc/rc.boot
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/mail
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/Mail
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/.xsession-errors
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/.xauth
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/.tcshrc
### No such file or directory
### Continuing...
### Warning: File system error.
### Filename: /root/.sawfish
### No such file or directory

In the above output, you should get "No such directory" error. To resolve this error, you will need to edit Tripwire policy configuration file and regenerate the configuration.

First, list out all the files and directory that does not exist by running the following command:

sh -c "tripwire --check | grep Filename > list.txt"

cat list.txt

You should see all the files and directories in the following output:

     Filename: /etc/rc.boot
     Filename: /root/mail
     Filename: /root/Mail
     Filename: /root/.xsession-errors
     Filename: /root/.xauth
     Filename: /root/.tcshrc
     Filename: /root/.sawfish
     Filename: /root/.pinerc
     Filename: /root/.mc
     Filename: /root/.gnome_private
     Filename: /root/.gnome-desktop
     Filename: /root/.gnome
     Filename: /root/.esd_auth
     Filename: /root/.elm
     Filename: /root/.cshrc
     Filename: /root/.bash_profile
     Filename: /root/.bash_logout
     Filename: /root/.amandahosts
     Filename: /root/.addressbook.lu
     Filename: /root/.addressbook
     Filename: /root/.Xresources
     Filename: /root/.Xauthority
     Filename: /root/.ICEauthority
     Filename: /proc/3776/fd/3
     Filename: /proc/3776/fdinfo/3
     Filename: /proc/3776/task/3776/fd/3
     Filename: /proc/3776/task/3776/fdinfo/3

Now, open the Tripwire policy configuration file twpol.txt.

nano /etc/tripwire/twpol.txt

Comment out the lines as shown below:

(
  rulename = "Boot Scripts",
  severity = $(SIG_HI)
)
{
        /etc/init.d             -> $(SEC_BIN) ;
        #/etc/rc.boot           -> $(SEC_BIN) ;
        /etc/rcS.d              -> $(SEC_BIN) ;
        /etc/rc0.d              -> $(SEC_BIN) ;
        /etc/rc1.d              -> $(SEC_BIN) ;
        /etc/rc2.d              -> $(SEC_BIN) ;
        /etc/rc3.d              -> $(SEC_BIN) ;
        /etc/rc4.d              -> $(SEC_BIN) ;
        /etc/rc5.d              -> $(SEC_BIN) ;
        /etc/rc6.d              -> $(SEC_BIN) ;
}


(
  rulename = "System boot changes",
  severity = $(SIG_HI)
)
{
        #/var/lock              -> $(SEC_CONFIG) ;
        #/var/run               -> $(SEC_CONFIG) ; # daemon PIDs
        /var/log                -> $(SEC_CONFIG) ;
}


(
  rulename = "Root config files",
  severity = 100
)
{
        /root                           -> $(SEC_CRIT) ; # Catch all additions to /root
        #/root/mail                     -> $(SEC_CONFIG) ;
        #/root/Mail                     -> $(SEC_CONFIG) ;
        #/root/.xsession-errors         -> $(SEC_CONFIG) ;
        #/root/.xauth                   -> $(SEC_CONFIG) ;
        #/root/.tcshrc                  -> $(SEC_CONFIG) ;
        #/root/.sawfish                 -> $(SEC_CONFIG) ;
        #/root/.pinerc                  -> $(SEC_CONFIG) ;
        #/root/.mc                      -> $(SEC_CONFIG) ;
        #/root/.gnome_private           -> $(SEC_CONFIG) ;
        #/root/.gnome-desktop           -> $(SEC_CONFIG) ;
        #/root/.gnome                   -> $(SEC_CONFIG) ;
        #/root/.esd_auth                        -> $(SEC_CONFIG) ;
        #/root/.elm                     -> $(SEC_CONFIG) ;
        #/root/.cshrc                   -> $(SEC_CONFIG) ;
        /root/.bashrc                   -> $(SEC_CONFIG) ;
        #/root/.bash_profile            -> $(SEC_CONFIG) ;
        #/root/.bash_logout             -> $(SEC_CONFIG) ;
        /root/.bash_history             -> $(SEC_CONFIG) ;
        #/root/.amandahosts             -> $(SEC_CONFIG) ;
        #/root/.addressbook.lu          -> $(SEC_CONFIG) ;
        #/root/.addressbook             -> $(SEC_CONFIG) ;
        #/root/.Xresources              -> $(SEC_CONFIG) ;
        #/root/.Xauthority              -> $(SEC_CONFIG) -i ; # Changes Inode number on login
        #/root/.ICEauthority                -> $(SEC_CONFIG) ;
}


(
  rulename = "Devices & Kernel information",
  severity = $(SIG_HI),
)
{
        /dev            -> $(Device) ;
#       /proc           -> $(Device) ;
}

Save and close the file, when you are finished. Then, recreate the encrypted policy file with the following command:

twadmin -m P /etc/tripwire/twpol.txt

Enter your site-key passphrase and press Enter.

Now, reinitialize the Tripwire database with the following command:

tripwire --init

Enter your local-key passphrase. You should see the following output:

Wrote database file: /var/lib/tripwire/mail.example.com.twd
The database was successfully generated.

Check System Files

Now, you will need to check the integrity of system files. You can do this with the following command:

tripwire --check

You should see the following output with no errors:

Total objects scanned:  27492
Total violations found:  0

===============================================================================
Object Summary: 
===============================================================================

-------------------------------------------------------------------------------
# Section: Unix File System
-------------------------------------------------------------------------------

No violations.

===============================================================================
Error Report: 
===============================================================================

No Errors

-------------------------------------------------------------------------------
*** End of report ***

Open Source Tripwire 2.4 Portions copyright 2000 Tripwire, Inc. Tripwire is a registered
trademark of Tripwire, Inc. This software comes with ABSOLUTELY NO WARRANTY;
for details use --version. This is free software which may be redistributed
or modified only under certain conditions; see COPYING for details.
All rights reserved.
Integrity check complete.

Now, create some file and directory with the following command:

touch test1.txt test2.txt test3.txt
mkdir test1 test2 test3

Next, check the system using Tripwire again:

tripwire --check

You should see files and directory which you have added earlier in the following output:

Total objects scanned:  27498
Total violations found:  7

===============================================================================
Object Summary: 
===============================================================================

-------------------------------------------------------------------------------
# Section: Unix File System
-------------------------------------------------------------------------------

-------------------------------------------------------------------------------
Rule Name: Root config files (/root)
Severity Level: 100
-------------------------------------------------------------------------------

Added:
"/root/test3"
"/root/test3.txt"
"/root/test1"
"/root/test2"
"/root/test2.txt"
"/root/test1.txt"

Modified:
"/root"

===============================================================================
Error Report: 
===============================================================================

No Errors

-------------------------------------------------------------------------------
*** End of report ***

Open Source Tripwire 2.4 Portions copyright 2000 Tripwire, Inc. Tripwire is a registered
trademark of Tripwire, Inc. This software comes with ABSOLUTELY NO WARRANTY;
for details use --version. This is free software which may be redistributed
or modified only under certain conditions; see COPYING for details.
All rights reserved.
Integrity check complete.

Add New Rules for Apache

Next, create a new Tripwire Rule for Apache named "Apache Ruleset" with severity 'High/SIG_HI' and all files on that directory is critical cannot be changed

First, open the Tripwire policy configuration file:

nano /etc/tripwire/twpol.txt

Add the following lines:

## Ruleset for Apache ##
(
  rulename = "Apache Ruleset",
  severity= $(SIG_HI)
)
{
        /var/www/html        -> $(SEC_CRIT);
}

Save and close the file, when you are finished. Then, regenerate the tripwire config file and reinitialize the Tripwire database with the following command:

twadmin -m P /etc/tripwire/twpol.txt
tripwire --init

Now, try to create a new file test.html inside /var/www/html directory with the following command:

echo "<h1> Test Apache</h1>" > /var/www/html/test.html

Next, check the system with the following command:

tripwire --check

You should get a notification about system violations with security level 100 in the following output:

Total objects scanned:  27502
Total violations found:  2

===============================================================================
Object Summary: 
===============================================================================

-------------------------------------------------------------------------------
# Section: Unix File System
-------------------------------------------------------------------------------

-------------------------------------------------------------------------------
Rule Name: Apache Ruleset (/var/www/html)
Severity Level: 100
-------------------------------------------------------------------------------

Added:
"/var/www/html/test.html"

Modified:
"/var/www/html"

===============================================================================
Error Report: 
===============================================================================

No Errors

-------------------------------------------------------------------------------
*** End of report ***

Open Source Tripwire 2.4 Portions copyright 2000 Tripwire, Inc. Tripwire is a registered
trademark of Tripwire, Inc. This software comes with ABSOLUTELY NO WARRANTY;
for details use --version. This is free software which may be redistributed
or modified only under certain conditions; see COPYING for details.
All rights reserved.
Integrity check complete.

Set Up E-mail Notification

By default, Tripwire provides a function 'emailto' in the configuration file to notify you through the mail. Before starting, test E-mail notification using the following command:

tripwire --test --email root@localhost

Now, check your mail with the following command:

tail -f /var/mail/root

You should see the following output:

From: "Open Source Tripwire(R) 2.4.2.2.2" <tripwire@mail.example.com>
To: root@localhost
Subject: Test email message from Tripwire
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Message-Id: <E1fyc6G-0000Uq-3Q@mail.example.com>

If you receive this message, email notification from tripwire. That means it is working correctly.

Next, you will need to configure Tripwire to send E-mail notification for Apache. You can do this by editing /etc/tripwire/twpol.txt file:

nano /etc/tripwire/twpol.txt

Make the following changes:

### Ruleset for Apache ###
(
  rulename = "Apache Ruleset",
  severity= $(SIG_HI),
  emailto = root@localhost
)
{
        /var/www/html        -> $(SEC_CRIT);
}

Save the file. Then, regenerate the configuration and reinitialize the Tripwire database with the following command:

twadmin -m P /etc/tripwire/twpol.txt
tripwire --init

Next, create some new file inside /var/www/html directory again and check the system manually using Tripwire and send the report over email.

tripwire --check --email-report

Now, check your mail using the following command:

tail -f /var/mail/root

You should see the following output:

Rule Name: Apache Ruleset (/var/www/html)
Severity Level: 100
-------------------------------------------------------------------------------

Added:
"/var/www/html/2"
"/var/www/html/3"
"/var/www/html/1"

Modified:
"/var/www/html"

===============================================================================
Error Report: 
===============================================================================

No Errors

-------------------------------------------------------------------------------
*** End of report ***

Open Source Tripwire 2.4 Portions copyright 2000 Tripwire, Inc. Tripwire is a registered
trademark of Tripwire, Inc. This software comes with ABSOLUTELY NO WARRANTY;
for details use --version. This is free software which may be redistributed
or modified only under certain conditions; see COPYING for details.
All rights reserved.
Integrity check complete.

Next, you can also configure cron that check your system every day and send a notification for an Apache rule violation to your email.

You can do this by editing /etc/crontab file:

nano /etc/crontab

Add the following line:

0 0 * * * tripwire --check --email-report

Save and close the file, then restart cron to apply the changes:

systemctl restart cron

Now, you will get notifications by e-mail every day.

Community

How to Install and Configure Tripwire IDS on Ubuntu 16.04

Prerequisites

Launch Alibaba Cloud ECS Instance

Install Tripwire

Configure Tripwire Policy

Check System Files

Add New Rules for Apache

Set Up E-mail Notification

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