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Inbound IP packets with a local host loopback address (127.0.0.0/8) must be blocked, denied, or dropped at the perimeter device.


Overview

Finding ID Version Rule ID IA Controls Severity
V-14689 NET0923 SV-15384r2_rule ECSC-1 High
Description
This type of IP address spoofing occurs when someone outside the network uses a local host 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 2017-03-09

Details

Check Text ( C-12851r3_chk )
Review the perimeter device configuration to ensure access control lists are configured to block, deny, or drop inbound IP addresses using the local host IP address space of 127.0.0.0/8. 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 127.0.0.0 0.255.255.255 any log
!
Fix Text (F-14154r2_fix)
Configure the perimeter device to ensure access control lists are configured to block, deny, or drop inbound IP addresses using the local host IP address space of 127.0.0.0/8. Depending on the security posture of the access control list, this requirement may be met explicitly or inexplicitly.