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Showing SKILL.md
| name | cis-ubuntu1604-v200-3-5-3-2-1 |
| description | Ensure iptables default deny firewall policy |
| category | cis-networking |
| version | 2.0.0 |
| author | cyberstrike-official |
| tags | ["cis","ubuntu","linux","ubuntu-16.04","firewall"] |
| cis_id | 3.5.3.2.1 |
| cis_benchmark | CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 |
| tech_stack | ["ubuntu","linux"] |
| cwe_ids | [] |
| chains_with | [] |
| prerequisites | [] |
| severity_boost | {} |
A default deny all policy on connections ensures that any unconfigured network usage will be rejected.
Notes:
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.
Run the following command and verify that the policy for the INPUT, OUTPUT, and FORWARD chains is DROP or REJECT:
iptables -L
Chain INPUT (policy DROP)
Chain FORWARD (policy DROP)
Chain OUTPUT (policy DROP)
Run the following commands to implement a default DROP policy:
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
None
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.