cyberstrikeus CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 3.5.3.2.3
Profile
- Level: Level 1 - Server, Level 1 - Workstation
- Assessment Status: Manual
Description
Configure the firewall rules for new outbound, and established connections.
Notes:
- 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.
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.
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
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
References
None
CIS Controls
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.