Open Source Tripwire®
Open Source Tripwire® is a security and data integrity tool for monitoring and alerting on file & directory changes. This project is based on code originally contributed by Tripwire, Inc. in 2000.
Overview
A Tripwire check compares the current filesystem state against a known baseline state, and alerts on any changes it detects. 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.
When an expected change occurs, such as upgrading a package, the baseline database can be updated to the new known-good state. The policy can also be updated, for example to reduce noise or cover a newly installed package.
Getting Started
This section covers manual setup of Open Source Tripwire. If installing via an RPM or Debian package, or via make install, a setup script will walk the user through the initial setup steps (key generation thru policy creation) and these will not need to be done by hand.
Generating Keys
The first step is to generate site and local key files. This is necessary because Tripwire policy, configuration, and database files are signed by default, and report files may also be signed. The site key is used to sign config and policy files, while databases and reports are signed with the local key. The idea here is that multiple machines can share a site key, but each will have its own local key. The policy and config files can then be created once and distributed across these machines.
A common practice is to include the hostname in the local key filename, as follows:
./twadmin --generate-keys -L /etc/tripwire/${HOSTNAME}-local.key
./twadmin --generate-keys -S /etc/tripwire/site.key
Creating a configuration file
The next step is to create a Tripwire config file. The config file contains a variety of settings including the locations of Tripwire binaries and key files, email report settings, and parameters that control baseline/check behavior. These settings are explained in detail in the twconfig(4) manual page.
This command line reads and validates the config text in /path/to/twcfg.txt, writes the results to tw.cfg, and signs the resulting file with the provided site key:
./twadmin --create-cfgfile -S /path/to/site.key /path/to/twcfg.txt
Generating a policy file
Now it's time to configure which files & directories OST will monitor. A few simple examples of policy rules:
/start/point -> $(IgnoreNone); # Get all attributes for this dir tree
/another/start -> +pinugS; # Get selected attributes for this dir tree
!/start/point/subdir/to/ignore; # Don't monitor this dir tree
The Tripwire policy language is documented in detail in the twpolicy(4) manual page, and default policies for most common operating systems are available in the OST project's policy subdirectory.
./twadmin --create-polfile -S /path/to/site.key /etc/tripwire/twpol.txt
Creating a baseline
The next step is to baseline the system for the first time. This step is necessary even if the previous steps are handled by a setup/install script.
./tripwire --init
This creates a database file in the configured directory, typically a file with a .twd extension in /var/lib/tripwire. The optional --verbose argument to init mode lists files and directories as they're being scanned.
Running a check
./tripwire --check
This runs a check, again with an optional --verbose option that displays what it's doing. Scan results are written to standard out, as well as a report file, which typically has a .twr extension and lives in /var/lib/tripwire/report. If email reporting is enabled, emails will be sent at the end of the check.
A common way to use OST is to set up a cron job to run checks periodically, emailing results to an administrative account. Note that the OST install script currently does not create any cron jobs, and this will need to be done by hand.
Printing a report
./twprint -m r -t [0-4] -r /path/to/reportfile.twr
The -t argument specifies the level of report verbosity, where 0 is a single line summary of the report contents, and 4 displays all gathered attributes on all changed objects. The report level defaults to 3 if not specified on the command line or via the REPORTLEVEL config file option.
Databases can be also printed with:
./twprint -m d -d /path/to/database.twd
Updating a database
The simplest form of update updates the database with all the changes in a report file:
./tripwire --update --accept-all
While a
./tripwire --update
brings up a text report in the user's preferred editor (as configured in the config file's EDITOR option), with a checkbox next to each detected change. After saving and exiting the editor, the database will only be updated for those objects that remain selected with an [x].
Updating a policy
Policy update mode modifies the current Tripwire policy without losing existing baselines.
./tripwire --update-policy updated-policy.txt
A check is run with the new policy as part of the update process. If this check detects changes, the default behavior is to display the changes and exit without updating the policy or database. To accept the changes and continue with the policy update, use the -Z low / --secure-mode low command line option.
Testing the email configuration
To test email configuration:
./tripwire --test --email [email protected]
This sends a test email to the specified address, using the email settings specified in the config file.
Building OST
Prerequisites
A C++ compiler. It's known to build with gcc and clang; OST should work with gcc versions as old as 2.95.2, although gcc older than version 3.1 will need an external STLPort package.
A POSIX-like operating system, including Linux, macOS, various BSDs, Solaris, AIX, HP-UX, Minix, Haiku, GNU/Hurd, and others. Windows users can build OST under Cygwin, although this does not provide support for monitoring the Registry or any Windows-specific file attributes.
Perl 5+ is needed to run the project's test suite.
Configuring & Building
OST uses a standard automake build, so the first configuration step will generally be:
./configure
Additional compiler arguments (such as Debian hardening options), non-default paths, and other options can be set up in this step. A ./configure --help lists the available configuration options.
The --prefix=/some/path option controls where a subsequent make install will install to, and where Tripwire binaries will look for a configuration file.
The --enable-static option causes the build to create statically linked binaries. This is often used as a security enhancement, so that Tripwire will not rely on the shared libraries on the machine. This is not possible on all platforms, as some (like macOS and Solaris) don't provide the necessary static libraries to link against.
Note that Linux systems that use NSS for name lookups will still employ shared libraries behind the scenes even when the OST binaries are statically linked. There have been occasional reports of segfaults when trying to do a name lookup in these circumstances, particularly when the binary was built on a different machine or it's trying to do an LDAP or NIS name lookup. If this occurs, there are two ways to work around it: Either switch to dynamic binaries, or set the Tripwire config file option RESOLVE_IDS_TO_NAMES=false, which tells OST to just watch numeric user & group IDs and not perform name lookups.
If the configure or make step fails with errors about the automake/autoconf version, it may be necessary to run the script
./touchconfig.sh
before building the project. This script simply touches files in the correct order such that their last change times are not all identical, and that they're different in the right order.
Then just
make
to build the project.
Running the test suites
the make check make target runs two things: The acceptance test suite in the src/test-harness directory, and unit tests by running twtest, which is built in the bin directory along with other Tripwire binaries. These tests can also be run separately:
./twtest runs all unit tests, while ./twtest list lists all available tests.
./twtest Groupname runs all tests in a group, and
./twtest Groupname/Testname just runs the specified test.
To run the acceptance tests manually, cd to the src/test-harness directory and run perl ./twtest.pl.
Deployment
The make install target installs OST to the configured location, and make install-strip installs and removes symbols from the Tripwire binaries. A make dist creates a gzipped source bundle.
Authors
License
The developer of the original code and/or files is Tripwire, Inc. Portions created by Tripwire, Inc. are copyright 2000-2018 Tripwire, Inc. Tripwire is a registered trademark of Tripwire, Inc. All rights reserved.
This program is free software. The contents of this file are subject to the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. You may redistribute it and/or modify it only in compliance with the GNU General Public License.
This program is distributed in the hope that it will be useful. However, this program is distributed "AS-IS" WITHOUT ANY WARRANTY; INCLUDING THE IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Please see the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
Nothing in the GNU General Public License or any other license to use the code or files shall permit you to use Tripwire's trademarks, service marks, or other intellectual property without Tripwire's prior written consent.
If you have any questions, please contact Tripwire, Inc. at either [email protected] or www.tripwire.org.