DenyHosts Setup

DenyHosts - Preventing Brute Forced Attacks
SSH Brute Force Attacks Protection using DenyHosts

You can easily block SSH server attacks including dictionary based attacks and brute force attacks using a Python based script – DenyHosts. It analyzes the sshd log messages to determine what hosts or IPs are attempting to hack into your system.

STEP 1: Open the package manager and install denyhosts STEP 2: Configure Denyhosts

The default configuration file is located at /etc/denyhosts.conf. You need to allow yourself access sshd.

Using your favorite text editor. Open /etc/hosts.allow (must be root user) and add the following line. sshd:  For Example: sshd:127.0.0.0 <-- this is the localhost feedback loop Save and close the file.

STEP 3: Open denyhosts.conf and change admin email. You will get an email on newly restricted hosts and IPs. If you do not want a email notification, leave it with #. Use your favorite text editor and open /etc/denyhosts.conf and edit (must be root) this line.

 # ADMIN_EMAIL = youremail@yourdomain.com

Save and close the file.

Your configuration file should look something like this: SECURE_LOG = /var/log/secure HOSTS_DENY = /etc/hosts.deny BLOCK_SERVICE = sshd DENY_THRESHOLD_INVALID = 3 DENY_THRESHOLD_VALID = 5 DENY_THRESHOLD_ROOT = 1 DENY_THRESHOLD_RESTRICTED = 1 WORK_DIR = /usr/share/denyhosts/data SUSPICIOUS_LOGIN_REPORT_ALLOWED_HOSTS=YES HOSTNAME_LOOKUP=YES LOCK_FILE = /var/lock/subsys/denyhosts ADMIN_EMAIL = youremail@yourdomain.com SMTP_HOST = localhost SMTP_PORT = 25 SMTP_FROM = DenyHosys  SMTP_SUBJECT = DenyHosts Report of your “System Name” AGE_RESET_VALID=5d AGE_RESET_ROOT=25d AGE_RESET_RESTRICTED=25d AGE_RESET_INVALID=10d DAEMON_LOG = /var/log/denyhosts DAEMON_SLEEP = 30s DAEMON_PURGE = 1h
 * 1) THESE SETTINGS ARE REQUIRED ############
 * 1) PURGE_DENY = 7d (This will never delete or purge entries)
 * 1) THESE SETTINGS ARE OPTIONAL ############
 * 1) THESE SETTINGS ARE SPECIFIC TO DAEMON MODE ##########

Now, start this utility by executing, in a console window as the root user type in:

service denyhosts start

Removing a blocked IP
If your IP is blocked and you want to remove it, follow below steps to remove your IP from DenyHosts Database.

STEP 1: Stop DenyHosts first, in a console window as the root user type in:

service denyhosts stop

STEP 2: Remove Your IP From /etc/hosts.deny

In your favorite text editor open /etc/hosts.deny Delete your IP address. Save and close the file.

STEP 3: You need to edit the following files using your favorite text editor and remove the lines containing the IP address. These files are found in the /var/lib/denyhosts folder (you must be the root user to edited these files)

Be sure to save each file you edit. 1.hosts 2.hosts-restricted 3.hosts-root 4.hosts-valid 5.users-hosts

STEP 4: Start DenyHosts by executing, in a console window as the root user type in:

service denyhosts start

That’s it…! You can access ssh service with same IP, which was earlier blocked !