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cis-ubuntu2004-v300-4-2-4

DevOps & Security
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Ensure ufw service is enabled

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_20.04_LTS_Benchmark_v3.0.0/cis-ubuntu2004-v300-4-2-4/SKILL.md

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CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.2.4

Profile

  • Level: Level 1 - Server, Level 1 - Workstation
  • Assessment Status: Automated

Description

UncomplicatedFirewall (ufw) is a frontend for iptables. ufw provides a framework for managing netfilter, as well as a command-line and available graphical user interface for manipulating the firewall.

Note:

  • When running ufw enable or starting ufw via its initscript, ufw will flush its chains. This is required so ufw can maintain a consistent state, but it may drop existing connections (eg ssh). ufw does support adding rules before enabling the firewall.
  • Run the following command before running ufw enable.
ufw allow proto tcp from any to any port 22
  • The rules will still be flushed, but the ssh port will be open after enabling the firewall. Please note that once ufw is 'enabled', ufw will not flush the chains when adding or removing rules (but will when modifying a rule or changing the default policy)
  • By default, ufw will prompt when enabling the firewall while running under ssh. This can be disabled by using ufw --force enable

Rationale

The ufw service must be enabled and running in order for ufw to protect the system

Impact

Changing firewall settings while connected over network can result in being locked out of the system.

Audit Procedure

Command Line

Run the following command to verify that the ufw daemon is enabled:

systemctl is-enabled ufw.service

Run the following command to verify that the ufw daemon is active:

systemctl is-active ufw

Run the following command to verify ufw is active:

ufw status

Expected Result

enabled
active
Status: active

Remediation

Command Line

Run the following command to unmask the ufw daemon:

systemctl unmask ufw.service

Run the following command to enable and start the ufw daemon:

systemctl --now enable ufw.service

Run the following command to enable ufw:

ufw enable

Default Value

Not applicable.

References

  1. http://manpages.ubuntu.com/manpages/precise/en/man8/ufw.8.html
  2. NIST SP 800-53 Rev. 5: SC-7
  3. STIG ID: UBTU-20-010434 | Rule ID: SV-238355r958672 | CAT II
  4. STIG ID: UBTU-22-251015 | Rule ID: SV-260515r958672 | CAT II

CIS Controls

v8 - 4.4 Implement and Manage a Firewall on Servers v8 - 4.5 Implement and Manage a Firewall on End-User Devices v7 - 9.4 Apply Host-based Firewalls or Port Filtering

MITRE ATT&CK Mappings: T1562, T1562.004 | TA0005 | M1018