Ubuntu Server 20.04 : SNORT , Tripwire install

1. Install SNORT

Snort is an open source network intrusion detection system that can perform real-time traffic analysis and packet logging over IP networks.

It can perform “protocol analysis”, “content search” and “matching” and can be used to detect a variety of attacks such as “buffer overflows”, “stealth port scans”, “CGI attacks”, “SMB probes”, “OS fingerprinting attempts”, “semantic URL attacks” and “server message block probes”.

1.1 Install

①Required library installation

# apt install -y gcc libpcre3-dev zlib1g-dev libluajit-5.1-dev \
libpcap-dev openssl libssl-dev libnghttp2-dev libdumbnet-dev \
bison flex libdnet autoconf libtool

②Create working directory

# mkdir /usr/src/snort_src
# cd /usr/src/snort_src

③Daq download and install
Download the latest DAQ source package from the Snort web site using the wget command.
If a new source is available, please replace the version number of the command

# wget https://www.snort.org/downloads/snort/daq-2.0.7.tar.gz
# tar -xvzf daq-2.0.7.tar.gz
# cd daq-2.0.7
# autoreconf -f -i
# ./configure && make && make install
# cd ../

④Download and install SNORT

# wget https://www.snort.org/downloads/snort/snort-2.9.19.tar.gz
# tar -xvzf snort-2.9.19.tar.gz
# cd snort-2.9.19
# ./configure –enable-sourcefire && make && make install
# ldconfig
# ln -s /usr/local/bin/snort /usr/sbin/snort

1.2 Setting up user and folder structures

In order to run Snort securely without root access, a new unprivileged user and a new user group for running the daemon must be created

# groupadd snort
# useradd snort -r -s /sbin/nologin -c SNORT_IDS -g snort
# mkdir -p /etc/snort/rules
# mkdir /var/log/snort
# mkdir /usr/local/lib/snort_dynamicrules
# mkdir /etc/snort/preproc_rules
# chmod -R 5775 /etc/snort
# chmod -R 5775 /var/log/snort
# chmod -R 5775 /usr/local/lib/snort_dynamicrules
# chown -R snort:snort /etc/snort
# chown -R snort:snort /var/log/snort
# chown -R snort:snort /usr/local/lib/snort_dynamicrules

Create the following files

# touch /etc/snort/rules/white_list.rules
# touch /etc/snort/rules/black_list.rules
# touch /etc/snort/rules/local.rules

1.3 Setting up the configuration file

Copy all files to the configuration directory.

# cp /usr/src/snort_src/snort*/etc/*.conf* /etc/snort
# cp /usr/src/snort_src/snort*/etc/*.map /etc/snort

1.4 Use of community rules

Get the freely available community rules.

①Retrieve the community rules and copy them to the configuration folder

# wget https://www.snort.org/rules/community -O ~/community.tar.gz
# tar -xvf ~/community.tar.gz -C ~/
# cp ~/community-rules/* /etc/snort/rules

②Comment out unwanted lines en masse

# sed -i ‘s/include \$RULE\_PATH/#include \$RULE\_PATH/’ /etc/snort/snort.conf


1.5 Retrieving registered user rules

Free registration on the website gives you access to an Oink code that allows you to download the registered user ruleset.

①Get Oinkcode
Register as a user on the official Snort website and get the Oinkcode you need to get the community rules
In order to download the latest rule files, you need to register as a user at the official Snort website.
Go to https://www.snort.org/ 

Click on “Sign In”

Click on “Sign Up”.

Enter your “Email”, “Password”, “Password confirmation” and check the other fields, then click “Sign Up”.

If the “Sign Up” is successful, you will receive the following email to your registered email address
Click on the link in the text

Enter your registration details and login

Click on your email address

Click on “Oinkcodes” and save the “Oinkcode” separately.

②Download the registered user rules
Replace the “oinkcode” in the following with the code you got above

# https://www.snort.org/rules/snortrules-snapshot-29181.tar.gz?oinkcode= oinkcode -O ~/registered.tar.gz

③Extract rules to configuration directory

# tar -xvf ~/registered.tar.gz -C /etc/snort

1.6 Configuration of network sets and rule sets

①Edit snort.conf

# vi /etc/snort/snort.conf

Editorial content

line 45 : to match the environment of your server
# Setup the network addresses you are protecting
ipvar HOME_NET 48
# Set up the external network addresses. Leave as “any” in most situations

Line 104-106
# Path to your rules files (this can be a relative path)
var RULE_PATH /etc/snort/rules
var SO_RULE_PATH /etc/snort/so_rules
var PREPROC_RULE_PATH /etc/snort/preproc_rules

Line 113,114
# Set the absolute path appropriately
var WHITE_LIST_PATH /etc/snort/rules
var BLACK_LIST_PATH /etc/snort/rules

Scroll down to Step #6 and configure the output of unified2 to be logged in the snort.log file name as follows
Line 526 : Additional entries
# unified2
# Recommended for most installs
output unified2: filename snort.log, limit 128

Finally, scroll to the bottom of the file to find a list of the rule sets included.
In order to allow Snort to read custom rules, you need to uncomment local.rules.
Line 547
include $RULE_PATH/local.rules

If you are using community rules, add them just below the local.rules line.
include $RULE_PATH/community.rules

②Configuration validation
Use the parameter -T to test the configuration and enable the test mode

# snort -T -c /etc/snort/rules/snort.conf

If you get a “file not found” error, copy the file that gives the error to /etc/snort/rules
I had an error with the following file

# cp /usr/src/snort_src/snort-2.9.19/etc/classification.config /etc/snort/rules
# cp /usr/src/snort_src/snort-2.9.19/etc/reference.config /etc/snort/rules
# cp /usr/src/snort_src/snort-2.9.19/etc/threshold.conf /etc/snort/rules
# cp /usr/src/snort_src/snort-2.9.19/etc/unicode.map /etc/snort/rules/

If you get an invalid error, you can do the following

# vi /etc/snort/rules/snort.conf
Line 322~324 : Change as follows
#decompress_swf {deflate lzma} \
decompress_swf {deflate} \
decompress_pdf {deflate}

Againe try

# snort -T -c /etc/snort/rules/snort.conf

When you run it, you will see a message like the following example

  –== Initialization Complete ==–
,,_   -*> Snort! <*-
o” )~  Version 2.9.19 GRE (Build 85)
””   By Martin Roesch & The Snort Team: http://www.snort.org/contact#team
    Copyright (C) 2014-2021 Cisco and/or its affiliates. All rights reserved.
    Copyright (C) 1998-2013 Sourcefire, Inc., et al.
    Using libpcap version 1.9.1 (with TPACKET_V3)
    Using PCRE version: 8.39 2016-06-14
    Using ZLIB version: 1.2.11

    Rules Engine: SF_SNORT_DETECTION_ENGINE Version 3.2 <Build 1>
    Preprocessor Object: SF_SDF Version 1.1 <Build 1>
    Preprocessor Object: SF_MODBUS Version 1.1 <Build 1>
    Preprocessor Object: SF_POP Version 1.0 <Build 1>
    Preprocessor Object: SF_FTPTELNET Version 1.2 <Build 13>
    Preprocessor Object: SF_SMTP Version 1.1 <Build 9>
    Preprocessor Object: SF_GTP Version 1.1 <Build 1>
    Preprocessor Object: SF_DNS Version 1.1 <Build 4>
    Preprocessor Object: SF_REPUTATION Version 1.1 <Build 1>
    Preprocessor Object: SF_DNP3 Version 1.1 <Build 1>
    Preprocessor Object: SF_IMAP Version 1.0 <Build 1>
    Preprocessor Object: SF_S7COMMPLUS Version 1.0 <Build 1>
    Preprocessor Object: SF_SSH Version 1.1 <Build 3>
    Preprocessor Object: SF_DCERPC2 Version 1.0 <Build 3>
    Preprocessor Object: appid Version 1.1 <Build 5>
    Preprocessor Object: SF_SIP Version 1.1 <Build 1>
    Preprocessor Object: SF_SSLPP Version 1.1 <Build 4>

Total snort Fixed Memory Cost – MaxRss:838424
Snort successfully validated the configuration!
Snort exiting

1.7 Testing the configuration

To test that Snort is logging alerts as intended, add a custom detection rule alert for incoming ICMP connections to the local.rules file

# vi /etc/snort/rules/local.rules
Add the following to the last line
alert icmp any any -> $HOME_NET any (msg:”ICMP test”; sid:10000001; rev:001;)

Test run

# snort -A console -i eno1 -u snort -g snort -c /etc/snort/snort.conf

Replace “eno1” with your own network interface.
If the terminal is left in this state and another PC on the same network (e.g. Windows) pings this server, the terminal running Snort will show the following notification for each ICMP call

Commencing packet processing (pid=131577)
12/15-21:27:03.928135 [**] [1:10000001:1] ICMP test [**] [Priority: 0] {ICMP} ->
12/15-21:27:03.928419 [**] [1:10000001:1] ICMP test [**] [Priority: 0] {ICMP} ->
12/15-21:27:04.931973 [**] [1:10000001:1] ICMP test [**] [Priority: 0] {ICMP} ->
12/15-21:27:04.932072 [**] [1:10000001:1] ICMP test [**] [Priority: 0] {ICMP} ->
Snort records alerts in a log under /var/log/snort/snort.log.<timestamp>.
The log can be read with the following command
# snort -r /var/log/snort/snort.log.<id_number>

1.8 Run Snort in background

Add a new Snort start-up script to run Snort as a service

# vi /lib/systemd/system/snort.service

Script content
eno1” is adapted to your environment

[Unit] Description=Snort NIDS Daemon
After=syslog.target network.target

[Service] Type=simple
ExecStart=/usr/local/bin/snort -q -u snort -g snort -c /etc/snort/snort.conf -i eno1

[Install] WantedBy=multi-user.target

Reflection of settings and start-up

# systemctl daemon-reload
# systemctl start snort

2.Install Tripwire

Install a system to detect tampering of Linux server files by crackers.
This time, we will introduce Tripwire, a host-type IDS (IDS=Intrusion Detection System) as a file tampering detection system.
Tripwire detects the addition/modification/deletion of files by creating a database of the file status at the time of deployment and comparing the database with the current status of the files.

2.1 Installation and configuration

# apt install tripwire

① Create site key
Tripwire requires a site passphrase to secure the “tw.cfg” tripwire configuration file and the “tw.pol” tripwire policy file.
Encrypts both files using the specified passphrase.
The site passphrase is also required for a single instance of tripwire.

②Local Key Passphrase
A local passphrase is required to protect the tripwire database and report files.
The local key used by tripwire to avoid unauthorised changes to the tripwire baseline database.

③tripwire configuration path
The tripwire configuration is stored in the /etc/tripwire/twcfg.txt file.
It is used to generate the encrypted configuration file tw.cfg.

④tripwire Policy Path
tripwire stores the policy in the /etc/tripwire/twpol.txt file.
This is used to generate the encrypted policy file tw.pol which is used by tripwire.

Installation will proceed.

2.2 Configuration file settings

①Tripwire configuration file (twcfg.txt)
The details of the tripwire configuration file (twcfg.txt) are as follows
The paths for the encrypted policy file (tw.pol), site key (site.key) and local key (hostname local.key) are as follows

ROOT =/usr/sbin   # Executable files
POLFILE =/etc/tripwire/tw.pol
DBFILE =/var/lib/tripwire/$(HOSTNAME).twd # Data pace file
REPORTFILE =/var/lib/tripwire/report/$(HOSTNAME)-$(DATE).twr
SITEKEYFILE =/etc/tripwire/site.key
LOCALKEYFILE =/etc/tripwire/$(HOSTNAME)-local.key
EDITOR =/usr/bin/editor
SMTPHOST =localhost

2.3 Initial setup, including key creation and database creation

①Edit twcfg.txt

# cd /etc/tripwire
# vi twcfg.txt
Line 9
Add “#” to the beginning of the line and “LOOSEDIRECTORYCHECKING =true” to the line below it
Line 12:Change as required (maximum report level: 4)

② Configuration file generation

# cd /etc/tripwire
# twadmin -m F -c tw.cfg -S site.key twcfg.txt
Please enter your site passphrase: <Site Key Passphrase>
Wrote configuration file: /etc/tripwire/tw.cfg

③ Optimise your policy
Use the following policy optimisation script to optimise your policy

# vi twpolmake.pl

Policy optimisation script content

# Tripwire Policy File customize tool
# —————————————————————-
# Copyright (C) 2003 Hiroaki Izumi
# This program is free software; you can redistribute it and/or
# modify it under 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.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# 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.

# —————————————————————-
# Usage:
#     perl twpolmake.pl {Pol file}
# —————————————————————-
open(POL,”$POLFILE”) or die “open error: $POLFILE” ;
my($myhost,$thost) ;
my($sharp,$tpath,$cond) ;
my($INRULE) = 0 ;
while (<POL>) {
    if (($thost) = /^HOSTNAME\s*=\s*(.*)\s*;/) {
        $myhost = `hostname` ; chomp($myhost) ;
        if ($thost ne $myhost) {
            $_=”HOSTNAME=\”$myhost\”;” ;
    elsif ( /^{/ ) {
        $INRULE=1 ;
    elsif ( /^}/ ) {
        $INRULE=0 ;
    elsif ($INRULE == 1 and ($sharp,$tpath,$cond) = /^(\s*\#?\s*)(\/\S+)\b(\s+->\s+.+)$/) {
        $ret = ($sharp =~ s/\#//g) ;
        if ($tpath eq ‘/sbin/e2fsadm’ ) {
            $cond =~ s/;\s+(tune2fs.*)$/; \#$1/ ;
        if (! -s $tpath) {
            $_ = “$sharp#$tpath$cond” if ($ret == 0) ;
        else {
            $_ = “$sharp$tpath$cond” ;
    print “$_\n” ;
close(POL) ;

# perl twpolmake.pl twpol.txt > twpol.txt.new
# twadmin -m P -c tw.cfg -p tw.pol -S site.key twpol.txt.new
Please enter your site passphrase: <Site Key Passphrase>
Wrote policy file: /etc/tripwire/tw.pol

④Create database

# tripwire -m i -s -c tw.cfg
Please enter your local passphrase: <Lokal Key Passphrase>

If it stops with an error in the middle of the process, use the “–v” option to display the progress and see which files stop with errors.
In our case, it stopped at a Snort-related file.

# chmod -R 5775 <Specify the absolute path to the file that causes the error>
# chown -R snort:snort <Specify the absolute path to the file that causes the error>

Paths and files that are expected to stop
After giving ownership and permissions to the above file, run the following again

# tripwire -m i -s -c tw.cfg
Please enter your local passphrase: <Lokal Key Passphrase>

When complete, the following will appear

Processing: /var/tmp
— Generating information for: /var/tmp
Processing: /home
— Generating information for: /home
Processing: /tmp
— Generating information for: /tmp
Wrote database file: /var/lib/tripwire/Lepard.twd
The database was successfully generated.

2.4 Run a check

①Create test file

# echo test > /root/test.txt

②Checking the operation of Tripwire

# tripwire -m c -s -c /etc/tripwire/tw.cfg

If successful, the following message will appear

Open Source Tripwire(R) Integrity Check Report
Report generated by: root
Report created on: Thu 16 Dec 2021 09:32:46 AM JST
Database last updated on: Never
Report Summary:
Host name: Lepard
Host IP address:
Host ID: None
Policy file used: /etc/tripwire/tw.pol
Configuration file used: /etc/tripwire/tw.cfg
Database file used: /var/lib/tripwire/Lepard.twd
Command line used: tripwire -m c -s -c /etc/tripwire/tw.cfg
Rule Summary:
Section: Unix File System
Rule Name Severity Level Added Removed Modified
——— ————– —– ——- ——–
Other binaries 66 0 0 0
Tripwire Binaries 100 0 0 0
Other libraries 66 0 0 0
Root file-system executables 100 0 0 0
* Tripwire Data Files 100 1 0 0
System boot changes 100 0 0 0
Root file-system libraries 100 0 0 0
Critical system boot files 100 0 0 0
Other configuration files 66 0 0 0
Boot Scripts 100 0 0 0
Security Control 66 0 0 0
* Root config files 100 1 0 0
Devices & Kernel information 100 0 0 0
Invariant Directories 66 0 0 0
Total objects scanned: 49813
Total violations found: 2
Object Summary:
# Section: Unix File System
Rule Name: Tripwire Data Files (/var/lib/tripwire/Lepard.twd)
Severity Level: 100
Rule Name: Root config files (/root)
Severity Level: 100
Error Report:
===============================================================No Errors
*** End of report ***
Open Source Tripwire 2.4 Portions copyright 2000-2018 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.

Delete the test file.

# rm -f /root/test.txt

2.5 Tripwire auto-run

①Create an autorun script (tripwire.sh) and run it automatically

# cd /opt/script
# vi tripwire.sh

Contents of the auto-run script (tripwire.sh)



# Passphrase settings
LOCALPASS=xxxxxxxx   # Local passphrase
SITEPASS=xxxxxxxx      # Site passphrase

cd /etc/tripwire

# Tripwire check run
tripwire -m c -s -c tw.cfg|mail -s “Tripwire(R) Integrity Check Report in `hostname`” root

# Policy file update
twadmin -m p -c tw.cfg -p tw.pol -S site.key > twpol.txt
perl twpolmake.pl twpol.txt > twpol.txt.new
twadmin -m P -c tw.cfg -p tw.pol -S site.key -Q $SITEPASS twpol.txt.new > /dev/null
rm -f twpol.txt* *.bak

# Database modernisation
rm -f /usr/local/tripwire/lib/tripwire/*.twd*
tripwire -m i -s -c tw.cfg -P $LOCALPASS

②Give execution permissions and run regularly with Cron

# chmod 700 tripwire.sh
# crontab -e
0 5 * * * /opt/script/tripwire.sh

Reference: Script for reporting results by email



# Passphrase settings
LOCALPASS=xxxxx    # Local passphrase
SITEPASS=xxxxx       # Site passphrase

#Specify email address for notification
MAIL=”<your mailaddress> ”

cd /etc/tripwire

# Tripwire check run
tripwire -m c -s -c tw.cfg|mail -s “Tripwire(R) Integrity Check Report in `hostname`” $MAIL

# Policy file update
twadmin -m p -c tw.cfg -p tw.pol -S site.key > twpol.txt
perl twpolmake.pl twpol.txt > twpol.txt.new
twadmin -m P -c tw.cfg -p tw.pol -S site.key -Q $SITEPASS twpol.txt.new > /dev/null
rm -f twpol.txt* *.bak

# データベース最新化
rm -f /usr/local/tripwire/lib/tripwire/*.twd*
tripwire -m i -s -c tw.cfg -P $LOCALPASS