Set configuration for loopback traffic

Classification:

compliance

Framework:

Control:

Description

Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network.

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 traffic should be seen, all other interfaces should ignore traffic on this network as an anti-spoofing measure.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

# Remediation is applicable only in certain platforms
if ( ! ( dpkg-query --show --showformat='${db:Status-Status}\n' 'nftables' 2>/dev/null | grep -q installed ) && ! ( dpkg-query --show --showformat='${db:Status-Status}\n' 'ufw' 2>/dev/null | grep -q installed ) ); then

iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
iptables -A INPUT -s 127.0.0.0/8 -j DROP

else
 >&2 echo 'Remediation is not applicable, nothing was done'
fi

Ansible playbook

The following playbook can be run with Ansible to remediate the issue.

- name: Gather the package facts
 package\_facts:
 manager: auto
 tags:
 - PCI-DSS-Req-1.3
 - PCI-DSSv4-1.4.1
 - medium\_severity
 - set\_loopback\_traffic

- name: Allow incoming traffic on the loopback interface
 ansible.builtin.iptables:
 chain: INPUT
 in\_interface: lo
 jump: ACCEPT
 when: ( not ( "nftables" in ansible\_facts.packages ) and not ( "ufw" in ansible\_facts.packages
 ) )
 tags:
 - PCI-DSS-Req-1.3
 - PCI-DSSv4-1.4.1
 - medium\_severity
 - set\_loopback\_traffic

- name: Allow outgoing traffic on the loopback interface
 ansible.builtin.iptables:
 chain: OUTPUT
 out\_interface: lo
 jump: ACCEPT
 when: ( not ( "nftables" in ansible\_facts.packages ) and not ( "ufw" in ansible\_facts.packages
 ) )
 tags:
 - PCI-DSS-Req-1.3
 - PCI-DSSv4-1.4.1
 - medium\_severity
 - set\_loopback\_traffic

- name: Drop incoming traffic from the localhost
 ansible.builtin.iptables:
 chain: INPUT
 source: 127.0.0.0/8
 jump: DROP
 when: ( not ( "nftables" in ansible\_facts.packages ) and not ( "ufw" in ansible\_facts.packages
 ) )
 tags:
 - PCI-DSS-Req-1.3
 - PCI-DSSv4-1.4.1
 - medium\_severity
 - set\_loopback\_traffic

Warning

Changing firewall settings while connected over network can result in being locked out of the system.