Tag: brute-force

Posted on

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

Posted on

Limiting the number of connections to SSH Server using Iptables

This is the quickest way to limit the number of connection to your SSH server with iptables.

[bash]
sudo /sbin/iptables -A INPUT -p tcp –syn –dport 22 -m connlimit –connlimit-above 5 -j REJECT
[/bash]

This will only allow up to 5 concurrent connections to the SSH server, subsequent connections will be rejected by iptables, thus this can thwarts Brute-force attempts to your server.

More Articles About Securing SSH Server

Posted on

How to Secure SSH server from Brute-Force and DDOS with Fail2ban ( Ubuntu )

Fail2ban is a security tool used for preventing brute-force attack and Distributed Denial of Service (DDoS) attack to your GNU/Linux box.

Fail2ban monitors failed login attempts and subsequently blocks the ip address from further logins. Although Fail2ban can also be used to secure other services in Ubuntu server, in this post, I will only focus on securing SSH server.

Step 1: Install Fail2ban and (optionally) sendmail

sudo apt-get install fail2ban
sudo apt-get install sendmail-bin

Step 2: Setting up Fail2ban

Next, you need to configure fail2ban by creating a copy of ‘jail.conf’ to ‘jail.local’

cd /etc/fail2ban
sudo cp jail.conf jail.local

Step 3: General fail2ban configuration

Edit fail2ban configuration file using your favorite text-edito (I personally use ‘nano’)

sudo nano /etc/jail.local

You can set IP address for fail2ban to ignore, IP addresses can be separated by space.

Bantime is the duration of time that you want fail2ban to block suspicious attempt, the value is in seconds
Maxretry is the number of failed attempts before fail2ban block the IP-address, in this case 3600 means 1-hour ban

# "ignoreip" can be an IP address, a CIDR mask or a DNS host
ignoreip = 127.0.0.1 192.168.1.1
bantime  = 3600
maxretry = 3

Step 4: Enabling ssh and ssh-ddos protection
Find ssh configuration under [ssh] heading, and enable it.

[ssh]
enabled = true
port    = ssh
filter  = sshd
logpath  = /var/log/auth.log
maxretry = 3

Similarly, you can also enable [ssh-dos] protection by changing the enabled value to “enabled = true”

[ssh-ddos]
enabled = true
port    = ssh
filter  = sshd-ddos
logpath  = /var/log/auth.log
maxretry = 2

Step 5: Enable Sending Notification Email (optional)
Optionally you can have fail2ban sends you notification email in case of suspicious login detected. To do that, you need to locate destemail settings and changed it to your email

destemail = security@mypapit.net

Fail2ban can use ‘sendmail’ and ‘mail’ application to send notification email

Step 6: (Re-)start Fail2ban
After all is done, you may save the file, and (re)start the fail2ban service

sudo /etc/init.d/fail2ban restart

You can test the configuration by trying to login into your box. You may also check fail2ban log in /var/logs/auth.log (or in other directory specified in jail.local)

For more information about fail2ban, you can read : the official fail2ban manual

Recommended Reading