Detections
Analytics
4.3.4 Ensure nftables loopback traffic is configured
Information
Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback networkLoopback 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.
Solution
Run the following script to implement the loopback rules:#!/usr/bin/env bash
{ l_hbfw=""
if systemctl is-enabled firewalld.service 2>/dev/null | grep -q 'enabled'; then
echo -e "
- FirewallD is in use on the system
- Recommendation is NA
- Remediation Complete" && l_hbfw="fwd"
elif systemctl is-enabled nftables.service | grep -q 'enabled'; then
l_hbfw="nft"
fi
if [ "$l_hbfw" = "nft" ]; then
l_ipsaddr="$(nft list ruleset | awk '/filter_IN_public_deny|hooks+inputs+/,/}s*(#.*)?$/' | grep -P -- 'iph+saddr')"
if ! nft list ruleset | awk '/hooks+inputs+/,/}s*(#.*)?$/' | grep -Pq -- 'H+h+"lo"h+accept'; then
echo -e "
- Enabling input to accept for loopback address"
nft add rule inet filter input iif lo accept
else
echo -e "
-nftables input correctly configured to accept for loopback address"
fi
if ! grep -Pq -- 'iph+saddrh+127.0.0.0/8h+(counterh+packetsh+d+h+bytesh+d+h+)?drop' <<< "$l_ipsaddr" && ! grep -Pq -- 'iph+daddrh+!=h+127.0.0.1h+iph+saddrh+127.0.0.1h+drop' <<< "$l_ipsaddr"; then
echo -e "
- Setting IPv4 network traffic from loopback address to drop"
nft add rule inet filter input ip saddr 127.0.0.0/8 counter drop
else
echo -e "
-nftables correctly configured IPv4 network traffic from loopback address to drop"
fi
if grep -Pq -- '^h*0h*$' /sys/module/ipv6/parameters/disable; then
l_ip6saddr="$(nft list ruleset | awk '/filter_IN_public_deny|hook input/,/}/' | grep 'ip6 saddr')"
if ! grep -Pq 'ip6h+saddrh+::1h+(counterh+packetsh+d+h+bytesh+d+h+)?drop' <<< "$l_ip6saddr" && ! grep -Pq -- 'ip6h+daddrh+!=h+::1h+ip6h+saddrh+::1h+drop' <<< "$l_ip6saddr"; then
echo -e "
- Setting IPv6 network traffic from loopback address to drop"
nft add rule inet filter input ip6 saddr ::1 counter drop
else
echo -e "
- nftables IPv6 network traffic from loopback address to drop"
fi
fi
fi
}
See Also
Item Details
Audit Name: CIS AlmaLinux OS 9 v2.0.0 L1 Workstation
Category: SECURITY ASSESSMENT AND AUTHORIZATION, SYSTEM AND COMMUNICATIONS PROTECTION
References: 800-53|CA-9, 800-53|SC-7, 800-53|SC-7(5), CSCv7|9.4
Plugin: Unix
Control ID: 84cb5841fdcea7a5c5149588b96eaadbf13d3dd5af5299da1a2fe4d1065a43dc