cyberstrikeus CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0 - Control 4.4.3.2
Profile
- Level: Level 1 - Server, Level 1 - Workstation
- Assessment Status: Automated
Description
Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network (::1).
Note:
- 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
Loopback traffic is generated between processes on machine and is typically critical to operation of the system. The loopback interface is the only place that loopback network (::1) traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.
Audit Procedure
Command Line
Run the following commands and verify output includes the listed rules in order (packet and byte counts may differ):
ip6tables -L INPUT -v -n
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all * * ::/0 ::/0
0 0 DROP all * * ::1 ::/0
ip6tables -L OUTPUT -v -n
Chain OUTPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all * lo ::/0 ::/0
- OR - Verify IPv6 is disabled: Run the following script. Output will confirm if IPv6 is enabled on the system.
#!/usr/bin/env bash
{
l_ipv6_enabled="is"
! grep -Pqs -- '^\h*0\b' /sys/module/ipv6/parameters/disable && l_ipv6_enabled="is not"
if sysctl net.ipv6.conf.all.disable_ipv6 | grep -Pqs -- "^\h*net\.ipv6\.conf\.all\.disable_ipv6\h*=\h*1\b" \
&& \
sysctl net.ipv6.conf.default.disable_ipv6 | grep -Pqs -- "^\h*net\.ipv6\.conf\.default\.disable_ipv6\h*=\h*1\b"; then
l_ipv6_enabled="is not"
fi
echo -e " - IPv6 $l_ipv6_enabled enabled on the system"
}
Expected Result
INPUT chain accepts loopback traffic and drops traffic from ::1. OUTPUT chain accepts outbound loopback traffic. Or IPv6 is disabled.
Remediation
Command Line
Run the following commands to implement the loopback rules:
ip6tables -A INPUT -i lo -j ACCEPT
ip6tables -A OUTPUT -o lo -j ACCEPT
ip6tables -A INPUT -s ::1 -j DROP
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, T1562.004 | TA0011 | M1031, M1037