The Cisco perimeter switch must be configured to filter traffic destined to the enclave in accordance with the guidelines contained in DoD Instruction 8551.1.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-101899	CISC-RT-000320	SV-111003r1_rule		Medium

Description
Vulnerability assessments must be reviewed by the System Administrator, and protocols must be approved by the Information Assurance (IA) staff before entering the enclave. ACLs are the first line of defense in a layered security approach. They permit authorized packets and deny unauthorized packets based on port or service type. They enhance the posture of the network by not allowing packets to reach a potential target within the security domain. The lists provided are highly susceptible ports and services that should be blocked or limited as much as possible without adversely affecting customer requirements. Auditing packets attempting to penetrate the network that are stopped by an ACL will allow network administrators to broaden their protective ring and more tightly define the scope of operation. If the perimeter is in a Deny-by-Default posture and what is allowed through the filter is in accordance with DoD Instruction 8551.1, and if the permit rule is explicitly defined with explicit ports and protocols allowed, then all requirements related to PPS being blocked would be satisfied.

Description

Vulnerability assessments must be reviewed by the System Administrator, and protocols must be approved by the Information Assurance (IA) staff before entering the enclave. ACLs are the first line of defense in a layered security approach. They permit authorized packets and deny unauthorized packets based on port or service type. They enhance the posture of the network by not allowing packets to reach a potential target within the security domain. The lists provided are highly susceptible ports and services that should be blocked or limited as much as possible without adversely affecting customer requirements. Auditing packets attempting to penetrate the network that are stopped by an ACL will allow network administrators to broaden their protective ring and more tightly define the scope of operation. If the perimeter is in a Deny-by-Default posture and what is allowed through the filter is in accordance with DoD Instruction 8551.1, and if the permit rule is explicitly defined with explicit ports and protocols allowed, then all requirements related to PPS being blocked would be satisfied.

STIG	Date
Cisco NX-OS Switch RTR Security Technical Implementation Guide	2020-05-20

Details

Check Text ( C-100787r1_chk )
Review the switch configuration to verify that the ingress ACL is in accordance with DoD 8551.1. Step 1: Verify that an inbound ACL is configured on all external interfaces. interface Ethernet2/2 description link to DISN no switchport ip access-group EXTERNAL_ACL in Step 2. Review the inbound ACL to verify that it is filtering traffic in accordance with DoD 8551.1. ip access-list EXTERNAL_ACL 10 permit tcp any any established 20 permit tcp x.11.1.1/32 eq bgp x.11.1.2/32 30 permit tcp x.11.1.1/32 x.11.1.2/32 eq bgp 40 permit icmp x.11.1.1/32 x.11.1.2/32 echo 50 permit icmp x.11.1.1/32 x.11.1.2/32 echo-reply 60 permit tcp any x.11.2.3/32 eq www 70 permit udp x.12.1.9/32 x.12.1.21/32 eq ntp … … < must be in accordance with DoD Instruction 8551.1> … 140 deny ip any any log If the switch does not filter traffic in accordance with the guidelines contained in DoD 8551, this is a finding.

Check Text ( C-100787r1_chk )

Review the switch configuration to verify that the ingress ACL is in accordance with DoD 8551.1.

Step 1: Verify that an inbound ACL is configured on all external interfaces.

interface Ethernet2/2
description link to DISN
no switchport
ip access-group EXTERNAL_ACL in

Step 2. Review the inbound ACL to verify that it is filtering traffic in accordance with DoD 8551.1.

ip access-list EXTERNAL_ACL
10 permit tcp any any established
20 permit tcp x.11.1.1/32 eq bgp x.11.1.2/32
30 permit tcp x.11.1.1/32 x.11.1.2/32 eq bgp
40 permit icmp x.11.1.1/32 x.11.1.2/32 echo
50 permit icmp x.11.1.1/32 x.11.1.2/32 echo-reply
60 permit tcp any x.11.2.3/32 eq www
70 permit udp x.12.1.9/32 x.12.1.21/32 eq ntp
…
… < must be in accordance with DoD Instruction 8551.1>
…
140 deny ip any any log

If the switch does not filter traffic in accordance with the guidelines contained in DoD 8551, this is a finding.

Fix Text (F-107581r1_fix)
Configure the switch to use an inbound ACL on all external interfaces as shown in the example below to restrict traffic in accordance with the guidelines contained in DOD Instruction 8551.1. SW2(config)# ip access-list EXTERNAL_ACL SW2(config-acl)# permit tcp any any established SW2(config-acl)# permit tcp x.11.1.1/32 eq bgp x.11.1.2/32 SW2(config-acl)# permit tcp x.11.1.1/32 x.11.1.2/32 eq bgp SW2(config-acl)# permit icmp x.11.1.1/32 x.11.1.2/32 echo SW2(config-acl)# permit icmp x.11.1.1/32 x.11.1.2/32 echo-reply SW2(config-acl)# permit tcp any x.11.2.3/32 eq www … … < must be in accordance with DoD Instruction 8551.1> … SW2(config-acl)# deny ip any any log SW2(config-acl)# exit SW1(config)#int e2/2 SW1(config-if)# ip access-group EXTERNAL_ACL in SW1(config-if)# end

Fix Text (F-107581r1_fix)

Configure the switch to use an inbound ACL on all external interfaces as shown in the example below to restrict traffic in accordance with the guidelines contained in DOD Instruction 8551.1.

SW2(config)# ip access-list EXTERNAL_ACL
SW2(config-acl)# permit tcp any any established
SW2(config-acl)# permit tcp x.11.1.1/32 eq bgp x.11.1.2/32
SW2(config-acl)# permit tcp x.11.1.1/32 x.11.1.2/32 eq bgp
SW2(config-acl)# permit icmp x.11.1.1/32 x.11.1.2/32 echo
SW2(config-acl)# permit icmp x.11.1.1/32 x.11.1.2/32 echo-reply
SW2(config-acl)# permit tcp any x.11.2.3/32 eq www
…
… < must be in accordance with DoD Instruction 8551.1>
…
SW2(config-acl)# deny ip any any log
SW2(config-acl)# exit
SW1(config)#int e2/2
SW1(config-if)# ip access-group EXTERNAL_ACL in
SW1(config-if)# end