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. By default UFW is disabled.
Gufw is a GUI that is available as a frontend.
Basic Syntax and Examples
Default rules are fine for the average home user
When
you turn UFW on, it uses a default set of rules (profile) that should
be fine for the average home user. That's at least the goal of the
Ubuntu developers. In short, all 'incoming' is being denied, with some
exceptions to make things easier for home users.
Enable and Disable
Enable UFW
To turn UFW on with the default set of rules:
sudo ufw enable
To check the status of UFW:
sudo ufw status verbose
The output should be like this:
youruser@yourcomputer:~$ sudo ufw status verbose [sudo] password for youruser: Status: active Logging: on (low) Default: deny (incoming), allow (outgoing) New profiles: skip youruser@yourcomputer:~$
Note
that by default, deny is being applied to incoming. There are
exceptions, which can be found in the output of this command:
sudo ufw show raw
You can also read the rules files in /etc/ufw (the files whose names end with .rules).
Disable UFW
To disable ufw use:
sudo ufw disable
Allow and Deny (specific rules)
Allow
sudo ufw allow/
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 packets on port 53
sudo ufw allow 53/udp
Deny
sudo ufw deny/
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:
less /etc/services
Allow by Service Name
sudo ufw allow
example: to allow ssh by name
sudo ufw allow ssh
Deny by Service Name
sudo ufw deny
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:
sudo ufw logging on
To disable logging use:
sudo ufw logging off
Advanced Syntax
You can also use a fuller syntax, specifying the source and destination addresses, ports and protocols.
Allow Access
This section shows how to allow specific access.
Allow by Specific IP
sudo ufw allow from
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 fromto port
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
Allow by specific port, IP address and protocol
sudo ufw allow fromto port proto
example: allow IP address 192.168.0.4 access to port 22 using TCP
sudo ufw allow from 192.168.0.4 to any port 22 proto tcp
Enable PING
Note: Security by obscurity may be of very little actual benefit with modern cracker scripts. By default, UFW allows ping requests. You may find you wish to leave (icmp) ping requests enabled to diagnose networking problems.
In order to disable ping (icmp) requests, you need to edit /etc/ufw/before.rules and remove the following lines:
# ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT -A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT -A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT -A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT -A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT
or change the "ACCEPT" to "DROP"
# ok icmp codes -A ufw-before-input -p icmp --icmp-type destination-unreachable -j DROP -A ufw-before-input -p icmp --icmp-type source-quench -j DROP -A ufw-before-input -p icmp --icmp-type time-exceeded -j DROP -A ufw-before-input -p icmp --icmp-type parameter-problem -j DROP -A ufw-before-input -p icmp --icmp-type echo-request -j DROP
Deny Access
Deny by specific IP
sudo ufw deny from
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 fromto port
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
Working with numbered rules
Listing rules with a reference number
You may use status numbered to show the order and id number of rules:
sudo ufw status numbered
Editing numbered rules
Delete numbered rule
You may then delete rules using the number. This will delete the first rule and rules will shift up to fill in the list.
sudo ufw delete 1
Insert numbered rule
sudo ufw insert 1 allow from
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 using tcp
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 proto tcp
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
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 proto tcp 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
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.
- UncomplicatedFirewall - UFW Project wiki page.
- Gufw - Graphic User Interface for UFW.
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