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cis-ubuntu1804-v220-3-4-1-7

DevOps & Security
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Ensure ufw default deny firewall policy

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_18.04_LTS_Benchmark_v2.2.0/cis-ubuntu1804-v220-3-4-1-7/SKILL.md

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CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.4.1.7

Description

A default deny all policy on connections ensures that any unconfigured network usage will be rejected.

Rationale

With a default accept policy the firewall will accept any packet that is not configured to be denied. It is easier to white list acceptable usage than to black list unacceptable usage.

Impact

Any port or protocol not explicitly allowed will be blocked. Ensure that all required ports and protocols are allowed before enabling the default deny policy.

Audit Procedure

Command Line

Run the following command and verify that the default policy is deny, reject, or disabled for incoming, outgoing, and routed directions:

ufw status verbose | grep 'Default:'

Expected Result

Default: deny (incoming), deny (outgoing), disabled (routed)

or

Default: reject (incoming), reject (outgoing), disabled (routed)

Remediation

Command Line

Run the following commands to set the default policy to deny:

ufw default deny incoming
ufw default deny outgoing
ufw default deny routed

Default Value

Default policy is allow.

References

  1. NIST SP 800-53 Rev. 5: CA-9, SC-7
  2. CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0

CIS Controls

Version 8

4.4 Implement and Manage a Firewall on Servers - Implement and manage a firewall on servers, where supported.

4.5 Implement and Manage a Firewall on End-User Devices - Implement and manage a host-based firewall or port-filtering tool on end-user devices.

Version 7

9.4 Apply Host-based Firewalls or Port Filtering - Apply host-based firewalls or port filtering tools on end systems, with a default-deny rule that drops all traffic except those services and ports that are explicitly allowed.

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

Assessment Status

Automated