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How to block an IP address with ufw on Ubuntu Linux server

I am using UFW to manage firewall on my Ubuntu Linux 12.04/14.04 LTS server. I need to block a specific IP address from accessing my server. How do I block an IP address using ufw?

UFW (Uncomplicated Firewall) is a front-end for iptables and is particularly well-suited for a single server or host-based firewalls. It is the default firewall configuration tool for Ubuntu Linux. The UFW developed for a new sysadmin with ease use in mind. It is a user-friendly way to create an IPv4 or IPv6 based firewall to protect the server.

ufw block specific IP address

The syntax is:
sudo ufw deny from {ip-address-here} to any
To block or deny all packets from 192.168.1.5, enter:
sudo ufw deny from 192.168.1.5 to any

Show firewall status including your rules

Verify newly added rules, enter:
$ sudo ufw status numbered
OR
$ sudo ufw status

Fig.01: ufw firewall status

Fig.01: ufw firewall status

ufw block specific IP and port number

The syntax is:
ufw deny from {ip-address-here} to any port {port-number-here}
To block or deny spammers IP address 202.54.1.5 to port 80, enter:
sudo ufw deny from 202.54.1.5 to any port 80
Again verify with the following command:
$ sudo ufw status numbered
Sample outputs:

Status: active
 
	 To                         Action      From
	 --                         ------      ----
[ 1] 192.168.1.10 80/tcp        ALLOW       Anywhere
[ 2] 192.168.1.10 22/tcp        ALLOW       Anywhere
[ 3] Anywhere                   DENY        192.168.1.5
[ 4] 80                         DENY IN     202.54.1.5

ufw deny specific IP, port number, and protocol

The syntax is:
sudo ufw deny proto {tcp|udp} from {ip-address-here} to any port {port-number-here}
For example block hacker IP address 202.54.1.1 to tcp port 22, enter:
$ sudo ufw deny proto tcp from 202.54.1.1 to any port 22
$ sudo ufw status numbered

ufw block subnet

The syntax is same:
$ sudo ufw deny proto tcp from sub/net to any port 22
$ sudo ufw deny proto tcp from 202.54.1.0/24 to any port 22

How do I delete blocked IP address or unblock an IP address again?

The syntax is:
$ sudo ufw status numbered
$ sudo ufw delete NUM

To delete rule number # 4, enter:
$ sudo ufw delete 4
Sample outputs:

Deleting:
 deny from 202.54.1.5 to any port 80
Proceed with operation (y|n)? y
Rule deleted

Tip: UFW NOT blocking an IP address

UFW (iptables) rules are applied in order of appearance, and the inspection ends immediately when there is a match. Therefore, for example, if a rule is allowing access to tcp port 22 (say using sudo ufw allow 22), and afterward another Rule is specified blocking an IP address (say using ufw deny proto tcp from 202.54.1.1 to any port 22), the rule to access port 22 is applied and the later rule to block the hacker IP address 202.54.1.1 is not. It is all about the order. To avoid such problem you need to edit the /etc/ufw/before.rules file and add a section to “Block an IP Address” after “# End required lines” section.
$ sudo vi /etc/ufw/before.rules
Find line that read as follows:

# End required lines

Append your rule to block spammers or hackers:

# Block spammers 
-A ufw-before-input -s 178.137.80.191 -j DROP
# Block ip/net (subnet) 
-A ufw-before-input -s 202.54.1.0/24 -j DROP

Save and close the file. Finally, reload the firewall:
$ sudo ufw reload

Sysadmin because even developers need heroes!!!

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{ 1 comment… add one }
  • P4 January 19, 2016, 9:06 pm

    Simple indeed. I’m still a fanboy of core commands because any command wrapper could be a target of potential attacker and altering a python3 script seem to be much easier than altering a binary.

    How would you block the whole AS address space for a given AS the easiest way?

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