Contents
Tripwire
1. Download & Install
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# cd /usr/local/src # wget https://rpmfind.net/linux/epel/9/Everything/x86_64/Packages/t/tripwire-2.4.3.7-16.el9.x86_64.rpm # rpm -Uvh tripwire-2.4.3.7-16.el9.x86_64.rpm |
2. Passphrase setting
Set site passphrase and local passphrase
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# tripwire-setup-keyfiles |
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---------------------------------------------- The Tripwire site and local passphrases are used to sign a variety of files, such as the configuration, policy, and database files. Passphrases should be at least 8 characters in length and contain both letters and numbers. See the Tripwire manual for more information. ---------------------------------------------- Creating key files... (When selecting a passphrase, keep in mind that good passphrases typically have upper and lower case letters, digits and punctuation marks, and are at least 8 characters in length.) Enter the site keyfile passphrase: ←Enter any "Site Passphrase" Verify the site keyfile passphrase: ←Enter "Site Passphrase" again Generating key (this may take several minutes)...Key generation complete. (When selecting a passphrase, keep in mind that good passphrases typically have upper and lower case letters, digits and punctuation marks, and are at least 8 characters in length.) Enter the local keyfile passphrase: ←Enter any "Local Passphrase" Verify the local keyfile passphrase: ←Enter "Local Passphrase" again Generating key (this may take several minutes)...Key generation complete. ---------------------------------------------- Signing configuration file... Please enter your site passphrase: ←Enter "Site Passphrase" Wrote configuration file: /etc/tripwire/tw.cfg A clear-text version of the Tripwire configuration file: /etc/tripwire/twcfg.txt has been preserved for your inspection. It is recommended that you move this file to a secure location and/or encrypt it in place (using a tool such as GPG, for example) after you have examined it. ---------------------------------------------- Signing policy file... Please enter your site passphrase: ←Enter "Site Passphrase" Wrote policy file: /etc/tripwire/tw.pol A clear-text version of the Tripwire policy file: /etc/tripwire/twpol.txt ～中略～ default values from the current configuration file are used. |
3. Tripwire Configuration
①Configuration File Edit
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# vi /etc/tripwire/twcfg.txt Line 9 LOOSEDIRECTORYCHECKING =false Change LOOSEDIRECTORYCHECKING =true Line 12 REPORTLEVEL =3 Change REPORTLEVEL =4 |
②reate a Tripwire configuration file (cryptographically signed version)
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# twadmin -m F -c /etc/tripwire/tw.cfg -S /etc/tripwire/site.key /etc/tripwire/twcfg.txt Please enter your site passphrase: ←Enter site passphrase Wrote configuration file: /etc/tripwire/tw.cfg |
③Delete Tripwire configuration file (text version)
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# rm -f /etc/tripwire/twcfg.txt |
④Policy File Settings
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# cd /etc/tripwire/ # vi twpolmake.pl |
Contents of twpolmake.pl
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#!/usr/bin/perl # $POLFILE=$ARGV[0]; open(POL,"$POLFILE") or die "open error: $POLFILE" ; my($myhost,$thost) ; my($sharp,$tpath,$cond) ; my($INRULE) = 0 ; while (<POL>) { chomp; if (($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) ; |
⑤Policy File Optimizations
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# perl /etc/tripwire/twpolmake.pl /etc/tripwire/twpol.txt > /etc/tripwire/twpol.txt.new |
⑥Create policy file (cryptographically signed version) based on optimized policy file
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# twadmin -m P -c /etc/tripwire/tw.cfg -p /etc/tripwire/tw.pol -S /etc/tripwire/site.key /etc/tripwire/twpol.txt.new Please enter your site passphrase: ←Enter local passphrase Wrote policy file: /etc/tripwire/tw.pol |
⑦Create database and check operation
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# tripwire -m i -s -c /etc/tripwire/tw.cfg Please enter your local passphrase: ←Enter local passphrase |
Create test files
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# echo test > /root/test.txt |
Check Tripwire operation
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# tripwire -m c -s -c /etc/tripwire/tw.cfg The following is displayed and test.txt is detected Open Source Tripwire(R) 2.4.3.7 Integrity Check Report Report generated by: root Report created on: Thu 12 Sep 2024 10:05:04 AM JST Database last updated on: Never =============================================================================== Report Summary: =============================================================================== Host name: Lepard Host IP address: 192.168.11.83 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 --------- -------------- ----- ------- -------- User binaries 66 0 0 0 Tripwire Binaries 100 0 0 0 Libraries 66 0 0 0 Operating System Utilities 100 0 0 0 File System and Disk Administraton Programs 100 0 0 0 Kernel Administration Programs 100 0 0 0 Networking Programs 100 0 0 0 System Administration Programs 100 0 0 0 Hardware and Device Control Programs 100 0 0 0 System Information Programs 100 0 0 0 (/sbin/runlevel) Application Information Programs 100 0 0 0 (/sbin/rtmon) Critical Utility Sym-Links 100 0 0 0 Shell Binaries 100 0 0 0 Critical system boot files 100 0 0 0 * Tripwire Data Files 100 1 0 0 System boot changes 100 0 0 0 OS executables and libraries 100 0 0 0 Security Control 100 0 0 0 Login Scripts 100 0 0 0 Critical configuration files 100 0 0 0 * Root config files 100 1 0 0 Invariant Directories 66 0 0 0 Temporary directories 33 0 0 0 Critical devices 100 0 0 0 (/proc/kcore) Total objects scanned: 98029 Total violations found: 2 =============================================================================== Object Summary: =============================================================================== ------------------------------------------------------------------------------- # Section: Unix File System ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- Rule Name: Tripwire Data Files (/var/lib/tripwire) Severity Level: 100 ------------------------------------------------------------------------------- Added: "/var/lib/tripwire/Lepard.twd" ------------------------------------------------------------------------------- Rule Name: Root config files (/root) Severity Level: 100 ------------------------------------------------------------------------------- Added: "/root/test.txt" =============================================================================== 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 test files
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# rm -f /root/test.txt |
⑧Tripwire Scheduled Scripts
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# cd /var/www/system # vi tripwire.sh |
Contents of tripwire.sh
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#!/bin/bash PATH=/usr/sbin:/usr/bin:/bin:/usr/local/tripwire/sbin # Passphrase setting LOCALPASS= ←local passphrase SITEPASS= ←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 Modernization 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 modernization rm -f /usr/local/tripwire/lib/tripwire/*.twd* tripwire -m i -s -c tw.cfg -P $LOCALPASS |
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# chmod 700 tripwire.sh # crontab -e 0 3 * * * /var/www/system/tripwire.sh |
Reference: Script for reporting results by e-mail
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#!/bin/bash PATH=/usr/sbin:/usr/bin:/bin:/usr/local/tripwire/sbin # Passphrase setting LOCALPASS=xxxxx # local passphrase SITEPASS=xxxxx # site passphrase # Designation of e-mail address to be notified 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 Modernization 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 modernization rm -f /usr/local/tripwire/lib/tripwire/*.twd* tripwire -m i -s -c tw.cfg -P $LOCALPASS |
Execute the following command to confirm that the mail has been received
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# /var/www/system/tripwire.sh |
Chkrootkit
Install a rootkit detection tool called chkrootkit to check whether a rootkit has been installed on the Linux server.
Since chkrootkit is checked using the following command, it is desirable to install it in the early stages after Linux installation, since it is useless after the command itself has been tampered with so that rootkit cannot be detected.
[Commands used by chkrootkit]
awk, cut, echo, egrep, find, head, id, ls, netstat, ps, strings, sed, uname
Note that chkrootkit can only detect known rootkits and cannot detect new rootkits.
①Download and install chkrootkit
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# cd /usr/local/src # wget https://launchpad.net/chkrootkit/main/0.55/+download/chkrootkit-0.55.tar.gz # tar xvf chkrootkit-0.55.tar.gz |
➁Create /root/bin directory and move chkrootkit command to that directory
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# mkdir -p /root/bin # mv chkrootkit-0.55/chkrootkit /root/bin |
➂Check chkrootkit.
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# chkrootkit | grep INFECTED If nothing is displayed, no problem. |
Checking `chsh'... INFECTED
The chsh command changes the shell. If you do not use it, rename the file /usr/bin/chsh to chsh.bak and the display will disappear.
There is no problem even if the file is not renamed.
④Create chkrootkit periodic execution script and change permissions
Create chkrootkit execution script in a directory where it is automatically executed daily
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# vi /etc/cron.daily/chkrootkit |
Scheduled Script Contents
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#!/bin/bash PATH=/usr/bin:/bin:/root/bin LOG=/tmp/$(basename ${0}) # Run chkrootkit chkrootkit > $LOG 2>&1 # log output cat $LOG | logger -t $(basename ${0}) # SMTPS bindshell false positive response if [ ! -z "$(grep 465 $LOG)" ] && \ [ -z $(/usr/sbin/lsof -i:465|grep bindshell) ]; then sed -i '/465/d' $LOG fi # Support for Suckit false positives when updating upstart package if [ ! -z "$(grep Suckit $LOG)" ] && \ [ -z "$(rpm -V `rpm -qf /sbin/init`)" ]; then sed -i '/Suckit/d' $LOG fi # Send mail to root only when rootkit is detected [ ! -z "$(grep INFECTED $LOG)" ] && \ grep INFECTED $LOG | mail -s "chkrootkit report in `hostname`" root |
Add execution permission to chkrootkit execution script
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# chmod 700 /etc/cron.daily/chkrootkit |
⑤Backup commands used by chkrootkit
If the commands used by chkrootkit are tampered with, rootkit will not be detected.
Back up these commands.
If necessary, run chkrootkit with the backed up command
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# cd /root # mkdir /root/chkrootkit_cmd # cp `which --skip-alias awk cut echo egrep find head id ls netstat ps strings sed ssh uname` chkrootkit_cmd/ # ls -l /root/chkrootkit_cmd/ total 2628 -rwxr-xr-x 1 root root 714968 Sep 12 10:11 awk -rwxr-xr-x 1 root root 48944 Sep 12 10:11 cut -rwxr-xr-x 1 root root 36328 Sep 12 10:11 echo -rwxr-xr-x 1 root root 32 Sep 12 10:11 egrep -rwxr-xr-x 1 root root 291592 Sep 12 10:11 find -rwxr-xr-x 1 root root 44840 Sep 12 10:11 head -rwxr-xr-x 1 root root 40656 Sep 12 10:11 id -rwxr-xr-x 1 root root 140936 Sep 12 10:11 ls -rwxr-xr-x 1 root root 161624 Sep 12 10:11 netstat -rwxr-xr-x 1 root root 144608 Sep 12 10:11 ps -rwxr-xr-x 1 root root 116736 Sep 12 10:11 sed -rwxr-xr-x 1 root root 863768 Sep 12 10:11 ssh -rwxr-xr-x 1 root root 32680 Sep 12 10:11 strings -rwxr-xr-x 1 root root 32416 Sep 12 10:11 uname |
⑥Run chkrootkit on the copied command
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# chkrootkit -p /root/chkrootkit_cmd | grep INFECTED |
⑦Compresses backed up commands
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# tar zcvf chkrootkit_cmd.tar.gz chkrootkit_cmd chkrootkit_cmd/ chkrootkit_cmd/awk chkrootkit_cmd/cut chkrootkit_cmd/echo chkrootkit_cmd/egrep chkrootkit_cmd/find chkrootkit_cmd/head chkrootkit_cmd/id chkrootkit_cmd/ls chkrootkit_cmd/netstat chkrootkit_cmd/ps chkrootkit_cmd/strings chkrootkit_cmd/sed chkrootkit_cmd/ssh chkrootkit_cmd/uname |
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# ls -l total 1816 -rw-------. 1 root root 1200 Sep 8 12:57 anaconda-ks.cfg drwxr-xr-x 2 root root 4096 Sep 12 10:10 bin drwxr-xr-x 2 root root 4096 Sep 12 10:11 chkrootkit_cmd -rw-r--r-- 1 root root 1226549 Sep 12 10:11 chkrootkit_cmd.tar.gz --------------------------------------------------------------- |
⑧Send chkrootkit use command (compressed version) to root by e-mail
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# echo|mail -a chkrootkit_cmd.tar.gz -s chkrootkit_cmd.tar.gz root |
⑨Download and save chkrootkit_cmd.tar.gz file to Windows
⑩Delete backed up commands on the server
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# rm -f chkrootkit_cmd.tar.gz |
Logwatch
①Install
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# dnf install logwatch |
②Edit configuration file
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# vi /etc/logwatch/conf/logwatch.conf Per line 51 Set "MailTo = root" as a comment and set the email address you want to receive notifications to the line below it. #MailTo = root MailTo = [Mail address] Per line 84 : Set the level of detail for log notifications #Detail = Low Detail = High |
③Output Logwatch reports
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# logwatch --output stdout |
It will appear as follows
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################### Logwatch 7.5.5 (01/22/21) #################### Processing Initiated: Thu Sep 12 10:15:06 2024 Date Range Processed: yesterday ( 2024-Sep-11 ) Period is day. Detail Level of Output: 10 Type of Output/Format: stdout / text Logfiles for Host: Lepard ################################################################## --------------------- Kernel Audit Begin ------------------------ Number of audit daemon starts: 1 Number of audit initializations: 1 **Unmatched Entries** auditd[818]: audit dispatcher initialized with q_depth=2000 and 1 active plugins: 1 Time(s) ---------------------- Kernel Audit End ------------------------- ------omission------ --------------------- Disk Space Begin ------------------------ Filesystem Size Used Avail Use% Mounted on /dev/mapper/ml-root 16G 7.6G 7.7G 50% / /dev/nvme0n1p2 974M 272M 636M 30% /boot /dev/nvme0n1p1 599M 7.0M 592M 2% /boot/efi ---------------------- Disk Space End ------------------------- --------------------- lm_sensors output Begin ------------------------ No sensors found! Make sure you loaded all the kernel drivers you need. Try sensors-detect to find out which these are. ---------------------- lm_sensors output End ------------------------- ###################### Logwatch End ######################### |
④Test to see if the report arrives at the address you set. Check if you receive a log report email like the one above.
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# /etc/cron.daily/0logwatch |
Introduce disk usage check script
1. Script Creation
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# cd /var/www/system # vi disk_capacity_check.sh |
Contents of disk_capacity_check.sh
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#!/bin/bash # Designation of e-mail address to be notified MAIL="<your mailaddress>" DVAL=`/bin/df / | /usr/bin/tail -1 | /bin/sed 's/^.* \([0-9]*\)%.*$/\1/'` if [ $DVAL -gt 80 ]; then echo "Disk usage alert: $DVAL %" | mail -s "Disk Space Alert in `hostname`" $MAIL fi |
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# chmod 700 disk_capacity_check.sh |
2. Execution Confirmation
①Check current usage rates
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# df -h |
It appears as follows
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Filesystem Size Used Avail Use% Mounted on devtmpfs 4.0M 0 4.0M 0% /dev tmpfs 872M 0 872M 0% /dev/shm tmpfs 349M 7.0M 342M 2% /run /dev/mapper/ml-root 16G 7.6G 7.7G 50% / /dev/loop1 39M 39M 0 100% /var/lib/snapd/snap/snapd/21759 /dev/loop0 45M 45M 0 100% /var/lib/snapd/snap/certbot/3834 /dev/loop2 64M 64M 0 100% /var/lib/snapd/snap/core20/2318 /dev/nvme0n1p2 974M 272M 636M 30% /boot /dev/nvme0n1p1 599M 7.0M 592M 2% /boot/efi tmpfs 175M 8.0K 175M 1% /run/user/1000 |
②Create a dummy file to achieve at least 80% utilization(In the example, the name is dummyfile and it is about 6G.)
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# dd if=/dev/zero of=dummyfile bs=1M count=6000 |
③check again
Confirm that it is above 80% by performing the following
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# df -h |
④Run check scripts
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# /var/www/system/disk_capacity_check.sh |
You will receive an email to the email address you have set up, stating something like "Disk usage alert: 89 %".
⑤Delete "dummyfile"
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# rm dummyfile |
⑥Periodic Execution Setting
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# crontab -e Add the following 30 2 * * * /var/www/system/disk_capacity_check.sh |