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1. title Uncomplicated Firewall - UFW

Introduction

For an introduction to firewalls, please see Firewall.

UFW - Uncomplicated Firewall

The default firewall configuration tool for Ubuntu is ufw. Developed to ease iptables firewall configuration, ufw provides a user friendly way to create an IPv4 or IPv6 host-based firewall. UFW by default is initially disabled.

Basic Syntax and Examples

Set Default Rule

Setting the default mode of ufw is recommended before turning it on Set Default Deny:

sudo ufw default deny

Set Default Allow:

sudo ufw default allow

Enable and Disable

Enable ufw

To turn UFW on:

sudo ufw enable

Unless you have used set the default to deny when you initially enable ufw it is in ALLOW mode, and will allow everything incoming and outgoing until you make rulesets.

Disable ufw

To disable ufw use:

sudo ufw disable

Allow and Deny

Allow

sudo ufw allow <port>/<optional: protocol>

example: To allow incoming tcp and udp packet on port 53

sudo ufw allow 53

example: To allow incoming tcp packets on port 53

sudo ufw allow 53/tcp

example: To allow incoming udp packes on port 53

sudo ufw allow 53/udp

Deny

sudo ufw deny <port>/<optional: protocol>

example: To deny tcp and udp packets on port 53

sudo ufw deny 53

example: To deny incoming tcp packets on port 53

sudo ufw deny 53/tcp

example: To deny incoming udp packets on port 53

sudo ufw deny 53/udp

Delete Existing Rule

To delete a rule, simply prefix the original rule with delete. For example, if the original rule was:

ufw deny 80/tcp

Use this to delete it:

sudo ufw delete deny 80/tcp

Services

You can also allow or deny by service name since ufw reads from /etc/services To see get a list of services:

cat /etc/services | less

Allow by Service Name

sudo ufw allow <service name>

example: to allow ssh by name

sudo ufw allow ssh

Deny by Service Name

sudo ufw deny <service name>

example: to deny ssh by name

sudo ufw deny ssh

Status

Checking the status of ufw will tell you if ufw is enabled or disabled and also list the current ufw rules that are applied to your iptables. To check the status of ufw:

sudo ufw status

Firewall loaded

To                         Action  From
--                         ------  ----
22:tcp                     DENY    192.168.0.1
22:udp                     DENY    192.168.0.1
22:tcp                     DENY    192.168.0.7
22:udp                     DENY    192.168.0.7
22:tcp                     ALLOW   192.168.0.0/24
22:udp                     ALLOW   192.168.0.0/24

if ufw was not enabled the output would be:

sudo ufw status
Status: inactive

Logging

To enable logging use:

ufw logging on

To disable logging use:

ufw logging off

Advanced Syntax

You can also use a fuller syntax, specifying the source and destination addresses and ports.

Allow Access

This section shows how to allow specific access.

Allow by Specific IP

sudo ufw allow <ip address>

example:To allow packets from 207.46.232.182:

sudo ufw allow from 207.46.232.182

Allow by Subnet

You may use a net mask :

sudo ufw allow from 192.168.1.0/24

Allow by specific port and IP address

sudo ufw allow from <ip address> to <protocol> port <port number>

example: allow ip address 192.168.0.4 access to port 22 for all protocols

sudo ufw allow from 192.168.0.4 to any port 22

Enable PING

Note: Security by obscurity may be of very little actual benefit with modern cracker scripts. By default, UFW blocks ping requests. You may find you wish to enable ping to diagnose networking problems. You need to edit /etc/ufw/before.rules and remove the commment on this line (remove the # in the front)

-A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT

Deny Access

Deny by specific IP

sudo ufw deny from <ip address>

example:To block packets from 207.46.232.182:

sudo ufw deny from 207.46.232.182

Deny by specific port and IP address

sudo ufw deny from <ip address> to <protocol> port <port number>

example: deny ip address 192.168.0.1 access to port 22 for all protocols

sudo ufw deny from 192.168.0.1 to any port 22

Advanced Blocking Rules

Blocking IP addresses is not so straight forward if you have an existing set of rules as IPTABLES matches in order. So if you started with default deny and added in port 80 for a public server :

sudo ufw allow 80

But then find IP address 111.222.3.44 is hacking your server :

sudo ufw deny 111.222.3.44

will do nothing (you allowed access with your first rule). You need to edit /etc/ufw/before.rules and add a section "Block IP" after "Drop INVALID packets" :

-A ufw-before-input -s 111.222.3.44 -j DROP #Assuming no loging is desired of course)
# drop INVALID packets
# uncomment to log INVALID packets
#-A ufw-before-input -m conntrack --ctstate INVALID -j LOG --log-prefix "[UFW B$
-A ufw-before-input -m conntrack --ctstate INVALID -j DROP

# Block IP
# This it is efective :)
-A ufw-before-input -s 111.222.3.44 -j DROP

Advanced Example

Scenario: You want to block access to port 22 from 192.168.0.1 and 192.168.0.7 but allow all other 192.168.0.x IPs to have access to port 22

sudo ufw deny from 192.168.0.1 to any port 22
sudo ufw deny from 192.168.0.7 to any port 22
sudo ufw allow from 192.168.0.0/24 to any port 22

This puts the specific rules first and the generic second. Once a rule is matched the others will not be evaluated (see manual below) so you must put the specific rules first. As rules change you may need to delete old rules to ensure that new rules are put in the proper order. To check your rules orders you can check the status; for the scenario the output below is the desired output for the rules to work properly

sudo ufw status
Firewall loaded

To                         Action  From
--                         ------  ----
22:tcp                     DENY    192.168.0.1
22:udp                     DENY    192.168.0.1
22:tcp                     DENY    192.168.0.7
22:udp                     DENY    192.168.0.7
22:tcp                     ALLOW   192.168.0.0/24
22:udp                     ALLOW   192.168.0.0/24

Scenario change: You want to block access to port 22 to 192.168.0.3 as well as 192.168.0.1 and 192.168.0.7.

sudo ufw delete allow from 192.168.0.0/24 to any port 22
sudo ufw status
Firewall loaded

To                         Action  From
--                         ------  ----
22:tcp                     DENY    192.168.0.1
22:udp                     DENY    192.168.0.1
22:tcp                     DENY    192.168.0.7
22:udp                     DENY    192.168.0.7

sudo ufw deny 192.168.0.3 to any port 22
sudo ufw allow 192.168.0.0/24 to any port 22
sudo ufw status

Firewall loaded

To                         Action  From
--                         ------  ----
22:tcp                     DENY    192.168.0.1
22:udp                     DENY    192.168.0.1
22:tcp                     DENY    192.168.0.7
22:udp                     DENY    192.168.0.7
22:tcp                     DENY    192.168.0.3
22:udp                     DENY    192.168.0.3
22:tcp                     ALLOW   192.168.0.0/24
22:udp                     ALLOW   192.168.0.0/24

If you simply add the deny rule the allow would have been above it and been applied instead of the deny

Other Resources

• For instructions on using ufw first see the official server guide.
• The most recent syntax and manual can be retrieved by getting the man page. Otherwise open a terminal window and type:

man ufw

• Firewall - wiki homepage for firewall related documentation.
• Iptables - interface to the netfilter subsystem in the Linux kernel.
• UbuntuWiki:UbuntuFirewall - UFW Project wiki page.

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