Inbound IP packets using RFC 1918 address space (10.0.0.0/8, 172.16.0.0 /12, and 192.168.0 /16) must be blocked, denied, or dropped at the perimeter device.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-14692	NET0927	SV-15393r2_rule	ECSC-1	High

Description
This type of IP address spoofing occurs when someone outside the network uses an RFC1918 address to gain access to systems or devices on the internal network. If the intruder is successful, they can intercept data, passwords, etc., and use that information to perform destructive acts on or to the network.

STIG	Date
Perimeter L3 Switch Security Technical Implementation Guide - Cisco	2018-11-28

Details

Check Text ( C-12860r2_chk )
Review the perimeter device configuration to ensure access control lists are configured to block, deny, or drop inbound IP addresses using the RFC1918 IP address space of 10.0.0.0/8, 172.16.0.0 /12, and 192.168.0 /16. Depending on the security posture of the access control list, this requirement may be met explicitly or inexplicitly. Config Example: interface FastEthernet 0/0 description to NIPRNet core router ip address 199.36.92.1 255.255.255.252 ip access-group 100 in ….. access-list 100 deny ip 10.0.0.0 0.255.255.255 any log access-list 100 deny ip 172.16.0.0 0.15.255.255 any log access-list 100 deny ip 192.168.0.0 0.0.255.255 any log

Check Text ( C-12860r2_chk )

Review the perimeter device configuration to ensure access control lists are configured to block, deny, or drop inbound IP addresses using the RFC1918 IP address space of 10.0.0.0/8, 172.16.0.0 /12, and 192.168.0 /16. Depending on the security posture of the access control list, this requirement may be met explicitly or inexplicitly.

Config Example:
interface FastEthernet 0/0
description to NIPRNet core router
ip address 199.36.92.1 255.255.255.252
ip access-group 100 in
…..
access-list 100 deny ip 10.0.0.0 0.255.255.255 any log
access-list 100 deny ip 172.16.0.0 0.15.255.255 any log
access-list 100 deny ip 192.168.0.0 0.0.255.255 any log

Fix Text (F-14157r3_fix)
Configure the perimeter device to ensure access control lists are configured to block, deny, or drop inbound IP addresses using the RFC1918 IP address space of 10.0.0.0/8, 172.16.0.0 /12, and 192.168.0 /16. Depending on the security posture of the access control list, this requirement may be met explicitly or inexplicitly.