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cis-ubuntu1804-v220-3-4-2-3

DevOps & Security
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Ensure iptables are flushed with nftables

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How to use this skill

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I want to install this Agent Skill for this project in Codex.

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-v220-3-4-2-3/SKILL.md

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CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.4.2.3

Description

nftables is a replacement for iptables, ip6tables, ebtables and arptables.

Rationale

It is possible to mix iptables and nftables. However, this increases complexity and is not recommended. Flushing all iptables rules clears the way for a clean nftables configuration.

Impact

Flushing all iptables rules will remove all firewall rules. Ensure that nftables rules are configured before flushing iptables.

Audit Procedure

Command Line

Run the following commands to verify iptables are flushed:

iptables -L

No rules should be returned.

ip6tables -L

No rules should be returned.

Expected Result

Both commands should return empty chain outputs with no rules:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Remediation

Command Line

Run the following commands to flush iptables:

iptables -F
ip6tables -F

Default Value

iptables rules are empty by default.

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

Manual