Cis Ubuntu1804 V220 3 4 3 2 3

CIS Ubuntu Linux 18.04 LTS Benchmark v2.2.0 - Control 3.4.3.2.3

Description

Configure the firewall rules for new outbound, and established connections.

Rationale

If rules are not in place for new outbound, and established connections all packets will be dropped by the default policy preventing network usage.

Impact

• Changing firewall settings while connected over network can result in being locked out of the system
• Remediation will only affect the active system firewall, be sure to configure the default policy in your firewall management to apply on boot as well

Audit Procedure

Command Line

Run the following command and verify all rules for new outbound, and established connections match site policy:

iptables -L -v -n

Expected Result

The output should show rules matching site policy for outbound and established connections.

Remediation

Command Line

Configure iptables in accordance with site policy. The following commands will implement a policy to allow all outbound connections and all established connections:

iptables -A OUTPUT -p tcp -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p udp -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p icmp -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -p icmp -m state --state ESTABLISHED -j ACCEPT

Default Value

No connection tracking rules exist 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