cyberstrikeus CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.3.7
Profile
- Level: Level 1 - Server, Level 1 - Workstation
- Assessment Status: Manual
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.
Audit Procedure
Command Line
Run the following commands and verify all rules for established incoming connections match site policy: site policy:
nft list ruleset | awk '/hook input/,/}/' | grep -E 'ip protocol (tcp|udp) ct state'
Output should be similar to:
ip protocol tcp ct state established accept
ip protocol udp ct state established accept
Run the following command and verify all rules for new and established outbound connections match site policy
nft list ruleset | awk '/hook output/,/}/' | grep -E 'ip protocol (tcp|udp) ct state'
Output should be similar to:
ip protocol tcp ct state established,related,new accept
ip protocol udp ct state established,related,new accept
Expected Result
Established incoming and new/established outgoing connection rules are present.
Remediation
Command Line
Configure nftables in accordance with site policy. The following commands will implement a policy to allow all outbound connections and all established connections:
nft add rule inet filter input ip protocol tcp ct state established accept
nft add rule inet filter input ip protocol udp ct state established accept
nft add rule inet filter output ip protocol tcp ct state new,related,established accept
nft add rule inet filter output ip protocol udp ct state new,related,established accept
Default Value
Not applicable.
References
- NIST SP 800-53 Rev. 5: CA-9, SC-7
CIS Controls
v8 - 4.4 Implement and Manage a Firewall on Servers v8 - 4.5 Implement and Manage a Firewall on End-User Devices v7 - 9.4 Apply Host-based Firewalls or Port Filtering
MITRE ATT&CK Mappings: T1562 | TA0011 | M1031, M1037