Download Wordlist for dictionary attack

Crackstation wordlist is one of the most (if not the most) comprehensive wordlist which can be used for the purpose of dictionary -attack on passwords.

The wordlist comes in two flavors:

  1. Full wordlist (GZIP-compressed (level 9). 4.2 GiB compressed. 15 GiB uncompressed)
  2. Human-password only wordlist (GZIP-compressed. 247 MiB compressed. 684 MiB uncompressed)

Personally, I’ve already downloaded the full wordlist via torrent, and tested it against few PDF files (using pdfcrack) and UNIX password cracking (using John), all my test cases were successful. In my opinion, the wordlist is comprehensive for my need.

Since it looked like it took a significant effort to compile this wordlist, I rather advocate those who are interested to donate/buy the wordlist from: https://crackstation.net/buy-crackstation-wordlist-password-cracking-dictionary.htm

Cracking PDF file with PDFCrack in Linux

I’ve come across an PDF which was sent to my email from an automated banking system. Unfortunately, the PDF file is encrypted and I’ve no way of knowing the password (or actually I’ve forgotten the password).

Fortunately, my Ubuntu box comes with application which allows me to crack the PDF file within a reasonable time.

Using ‘pdfcrack’ to crack PDF file

You need to install pdfcrack to crack pdf file. In Ubuntu/Debian system, you simply need to run

sudo apt-get -y install pdfcrack

Then for actual cracking, you can run

pdfcrack -n5 -m10 encrypted.pdf

Where -n [minimum length] to brute-force, and -m [maximum length] to brute-force.

pdfcrack can also accept a file input containing list of words (dictionary attack). For dictionary-attack just run

pdfcrack --wordlist=dictionary.txt encrypted.pdf

Securing SSH port and limiting IP address connection with Firewall in Ubuntu

UFW: Securing SSH
UFW or Uncomplicated Firewall is a firewall package in Ubuntu. UFW can be used to secure SSH ports in Ubuntu server.

In order to secure OpenSSH, we must first disable UFW and allow all SSH rule.

sudo ufw disable
sudo ufw delete allow ssh

Then we add IP Address to be allowed to connect to SSH port. In this case I assume that “192.168.1.10” would be allowed to be connected to the server. You can replace IP Address, with any IP Address that you prefer.

sudo ufw allow from 192.168.1.10 to any port ssh

You can also add other IP Address that can be connected to SSH port. In this case, I chose em>”172.25.100.1″.

sudo ufw allow from 172.25.100.1 to any port ssh

Alternatively, you could also specify port number and protocol

sudo ufw allow from 192.168.1.10 to any port 22 proto tcp

Only allow SSH connections from certain subnets

sudo ufw allow from 192.168.1.0/24 to any port 22 proto tcp

Note: Adding firewall rules to only allow SSH connection from certain subnets would increase the server security, further reducing brute-force attack.

Further Reading: Ubuntu Server Administrator Reference

Solving “Connection is encrypted using obsolete cipher suite” warning from Chrome

Here is a how to on how to solve the dreaded warning “Your connection is encrypted using obsolete cipher suit” from Google Chrome.

Firstly the warning had nothing to do with using cheap or self-signed TLS/SSL security certificate, but it has to do with cipher suite used on the server part.

obsolete-cipher-suite

So if you are a system administrator, you can edit the site config to include a more modern cipher.

NGINX Server

Using nginx, add the line containing “ssl_cipers” to the site config.

# /etc/nginx/sites-enable/example.conf 
server {
 listen 443 ssl;
 root /var/www/example.com/;
 server_name example.com;
   ssl_ciphers 'ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA';

        ssl_protocols TLSv1.1 TLSv1.2;
        ssl_prefer_server_ciphers on;
...
...
...

}

sudo service nginx restart

Apache HTTP Server

For those who are using Apache HTTP server, you can edit the VirtualHost file from “/etc/apache2/sites-enable/” directory.

<VirtualHost *:443>
    ...
    SSLEngine on
    SSLCertificateFile      /path/to/signed_certificate
    SSLCertificateChainFile /path/to/intermediate_certificate
    SSLCertificateKeyFile   /path/to/private/key
    SSLCACertificateFile    /path/to/all_ca_certs

    # Intermediate configuration, tweak to your needs
    SSLProtocol             all -SSLv2 -SSLv3
    SSLCipherSuite          ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA
    SSLHonorCipherOrder     on
    SSLCompression          off

    # OCSP Stapling, only in httpd 2.3.3 and later
    SSLUseStapling          on
    SSLStaplingResponderTimeout 5
    SSLStaplingReturnResponderErrors off
    # On Apache 2.4+, SSLStaplingCache must be set *outside* of the VirtualHost
    SSLStaplingCache        shmcb:/var/run/ocsp(128000)
 
    # Enable this if your want HSTS (recommended)
    # Header add Strict-Transport-Security "max-age=15768000"
 
    ...
</VirtualHost>

You can restart Apache HTTP server by running

sudo service apache2 restart

How to send fail2ban notification with Telegram (telegram-cli)

This is a a guide to integrate Telegram messaging service Fail2Ban. With this integration, Fail2Ban notification will be sent through Telegram services.

t_logo

Requirements

  1. You need to have Fail2ban installed in your systems.
  2. Install or compile “telegram-cli”, refer to this guide to compile telegram-cli or install it from *.deb (Ubuntu LTS) AMD64

Setting Up Fail2Ban with Telegram

After installing ‘telegram-cli’ and its requirements, you should proceed to add ‘telegram.conf’ config in /etc/fail2ban/action.d

The content of telegram.conf is as follows.

#
# /etc/fail2ban/action.d/telegram.conf
#
# Author: Toon Ketels
# Modified by: Mohammad Hafiz bin Ismail [mypapit @gmail.com]
#
# $Revision$
#

[Definition]

# Option:  actionstart
# Notes.:  command executed once at the start of Fail2Ban.
# Values:  CMD
#
actionstart = /usr/share/fail2ban/fail2ban-telegram.sh start

# Option:  actionstop
# Notes.:  command executed once at the end of Fail2Ban
# Values:  CMD
#
actionstop = /usr/share/fail2ban/fail2ban-telegram.sh stop

# Option:  actioncheck
# Notes.:  command executed once before each actionban command
# Values:  CMD
#
actioncheck =

# Option:  actionban
# Notes.:  command executed when banning an IP. Take care that the
#          command is executed with Fail2Ban user rights.
# Tags:    [ip]  IP address
#          [failures]  number of failures
#          [time]  unix timestamp of the ban time
# Values:  CMD
#
actionban = /usr/share/fail2ban/fail2ban-telegram.sh ban [ip]

# Option:  actionunban
# Notes.:  command executed when unbanning an IP. Take care that the
#          command is executed with Fail2Ban user rights.
# Tags:    [ip]  IP address
#          [failures]  number of failures
#          [time]  unix timestamp of the ban time
# Values:  CMD
#
actionunban = /usr/share/fail2ban/fail2ban-telegram.sh unban [ip]

[Init]

init = 'Fail2Ban Telegram plugins activated"


Then, you need to create a script file in /usr/share/fail2ban/fail2ban-telegram.sh.

#!/bin/bash
# /usr/share/fail2ban/fail2ban-telegram.sh
#
# Sends text messages using telegram api
# to alert server administrator of ip banning.
#
# Requires one argument, one of the following:
#  start
#  stop
#  ban
#  unban
#
# Optional second argument: IP for ban/unban




#replace this with your own telegram contact

to=Telegram_peer_replace_this

# Display usage information
function show_usage {
  echo "Usage: $0 action [ip]"
  echo "Where action is start, stop, ban, unban"
  echo "and ip is optional passed to ban, unban"
  exit
}



# Actually send telegram messages
# Expects the telegram content (body) to be passed
# as argument.
function send_telegram {

  msg="[`date -Iminutes`] - `hostname`:  Notice: $1 "
  echo "$msg" >> /var/log/fail2ban-telegram.log
 (echo "contact_list";sleep 30;echo "msg $to $msg"; echo "safe_quit") | telegram-cli
  exit
}



# Check for script arguments
if [ $# -lt 1 ]
then
  show_usage
fi



# Take action depending on argument
if [ "$1" = 'start' ]
then
  message="Fail2ban just started."
  send_telegram "$message"
elif [ "$1" = 'stop' ]
then
  message="Fail2ban just stopped."
  send_telegram "$message"
elif [ "$1" = 'ban' ]
then
  message=$([ "$2" != '' ] && echo "Fail2ban just banned $2" || echo 'Fail2ban just banned an ip.' )
  send_telegram "$message"
elif [ "$1" = 'unban' ]
then
  message=$([ "$2" != '' ] && echo "Fail2ban just unbanned $2" || echo "Fail2ban just unbanned an ip." )
  send_telegram "$message"
else
  show_usage
fi

After that, you need to ensure that the script is executable, by running.

sudo chmod a+rwx /usr/share/fail2ban/fail2ban-telegram.sh

Then, you need to edit “/etc/fail2ban/jail.conf” file to hook the action plugin with events. In this case, I choose the ssh and sshd events.

sudo nano -c /etc/fail2ban/jail.conf

Then proceed to find the [ssh] and [ssh-ddos] part. Add ‘telegram’ config in the file. Replace the “webmaster@example.com” email address with your email address.

[ssh]

enabled  = true
port     = ssh
filter   = sshd
logpath  = /var/log/auth.log
maxretry = 3
action = mail-whois[name=SSH, dest=webmaster@example.com]
         telegram

Now go to the “ssh-ddos” section, repeat the same step.

[ssh-ddos]

enabled  = true
port     = ssh
filter   = sshd-ddos
logpath  = /var/log/auth.log
maxretry = 4
action = mail-whois[name=SSH, dest=webmaster@example.com]
         telegram

Finishing up: Restart Fail2Ban

Finish up by restarting fail2ban server, and if you done it correctly you will be receiving both telegram messages and email notification regarding fail2ban startup!

sudo service fail2ban restart

Sample Screenshot

telegram-fail2ban

Congratulations!!

How to quickly become firewall expert with UFW !

Uncomplicated Firewall (UFW) is a helper tool which allows you to quickly setup iptables firewall in any Ubuntu server. It is installed by default and it allows you to secure your server at no time!

Basic UFW

Basic UFW: Check Status
You can check UFW by running this command. The verbose argument prints additional information such as UFW profiles, logging settings.

The ‘numbered’ argument prints the list of rules with line number. I’ll explain later on the use of this feature.

sudo ufw status
sudo ufw status verbose
sudo ufw status  numbered

Basic UFW: Enable and Disable Firewall
You can easily enable and disable firewall by specifying ‘disable’ and ‘enable’ argument.

Warning : Please do not enable UFW if you’re connecting using SSH connection to your Ubuntu box, you might be disconnected.

sudo ufw disable
sudo ufw enable

Basic UFW: Setting up default rule and Enabling SSH
A lot of you might be connecting to Ubuntu box using SSH connections, so the first step is to setup a default rule and enabling SSH connection.

Deny incoming connection

sudo ufw default deny incoming

Allow incoming SSH connection

sudo ufw allow ssh

Alternatively you can write:

sudo ufw allow 22/tcp

Finally, enable firewall

sudo ufw enable

You can check the firewall rules by running

sudo ufw status

Basic UFW: Enabling other service: HTTP, HTTPS

Enabling web server port and https is as easy as running

sudo ufw allow http
sudo ufw allow https

Basic UFW: Deleting rule
You can delete UFW rule by running

sudo ufw delete allow https

or by specifying its port and protocol

sudo ufw delete allow 443/tcp

Additionally you could also delete rule using its number by running “ufw status numbered” first

sudo ufw status numbered
ufw status numbered
Status: active

     To                         Action      From
     --                         ------      ----
[ 1] 22                         ALLOW IN    Anywhere
[ 2] 22/tcp                     ALLOW IN    Anywhere
[ 3] 443                        ALLOW IN    Anywhere
[ 4] 22 (v6)                    ALLOW IN    Anywhere (v6)
[ 5] 22/tcp (v6)                ALLOW IN    Anywhere (v6)
[ 6] 443 (v6)                   ALLOW IN    Anywhere (v6)

Then pick a firewall rule based on its number to delete, I picked number 3 and 6, because I want to delete https rule

sudo ufw delete 3
sudo ufw delete 6

UFW will print a confirmation prompt and you can continue deleting the firewall rules

/home/mypapit# ufw delete 6
Deleting:
 allow 443
Proceed with operation (y|n)? y   
Rule deleted (v6)

/home/mypapit# ufw delete 3
Deleting:
 allow 443
Proceed with operation (y|n)? y
Rule deleted

Intermediate UFW

Intermediate UFW: Deny access from ip address or ip block
You can prevent certain ip address or ip blocks / subnets from reaching your server by running:

sudo ufw deny from 172.18.44.12

Deny an ip address subnet

sudo ufw deny from 172.18.44.0/24

Deny an ip address subnet, example #2

sudo ufw deny from 172.16.0.0/16

Intermediate UFW: Allow services to be connected from certain ip address or subnet
In this case, I will only allow certain ip address to connect to my SSH port.

First we delete the old – “allow all” SSH rule

sudo ufw disable
sudo ufw delete allow ssh

Then we add ip address to be allowed to connect to SSH port

sudo ufw allow from 192.168.20.40 to any port ssh

Alternatively, you could also specify port number and protocol

sudo ufw allow from 192.168.20.40 to any port 22 proto tcp

Only allow SSH connections from certain subnets

sudo ufw allow from 192.168.20.0/24 to any port 22 proto tcp

Note: Adding firewall rules to only allow SSH connection from certain subnets would increase the server security, further reducing brute-force attack.

Further Reading: Ubuntu Server Administrator Reference

Generating TLS/SSL Self Signed Certificate for Nginx in Ubuntu LTS

This post concerns on generating self-signed TLS/SSL certificate for Nginx in Ubuntu LTS and assumes that you’ve configured nginx server with a default site.

Step 1: Generate OpenSSL certificate

sudo mkdir /etc/nginx/ssl
sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/nginx/ssl/nginx.key -out /etc/nginx/ssl/nginx.crt

You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:CA
Locality Name (eg, city) []:Palo Alto
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Mypapit LLC
Organizational Unit Name (eg, section) []:Billing
Common Name (e.g. server FQDN or YOUR name) []:Mypapit
Email Address []:mypapit+cert@gmail.com

Step 2: Edit nginx site config

You can edit nginx site config here, replace ‘default’ with your own server config.


sudo nano -c /etc/nginx/sites-enable/default

You will see this server block.


server {
        listen 80;
        listen [::]:80;
        server_name your_domain.com;
        root /var/www/your_domain.com;
        index index.html index.htm;

...
...
}

Add additional line (in italic)

server {
        listen 80;
        listen [::]:80;

    listen 443 ssl;

       server_name your_domain.com;
        root /var/www/your_domain.com;
      index index.html index.htm;

        ssl_certificate /etc/nginx/ssl/nginx.crt;
        ssl_certificate_key /etc/nginx/ssl/nginx.key;
        ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
        ssl_prefer_server_ciphers on;
        add_header Strict-Transport-Security max-age=31536000;



...
...
}

Save file, and restart nginx server

sudo nginx -t
sudo service nginx restart

Test configuration by going to https://your_domain.com.

Done!

Bonus: Add HSTS header and Serve only TLS

HSTS header