The Cisco perimeter router must be configured to restrict it from accepting outbound IP packets that contain an illegitimate address in the source address field via egress filter or by enabling Unicast Reverse Path Forwarding (uRPF).

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-217005	CISC-RT-000310	SV-217005r531087_rule		High

Description
A compromised host in an enclave can be used by a malicious platform to launch cyberattacks on third parties. This is a common practice in "botnets", which are a collection of compromised computers using malware to attack other computers or networks. DDoS attacks frequently leverage IP source address spoofing to send packets to multiple hosts that in turn will then send return traffic to the hosts with the IP addresses that were forged. This can generate significant amounts of traffic. Therefore, protection measures to counteract IP source address spoofing must be taken. When uRPF is enabled in strict mode, the packet must be received on the interface that the device would use to forward the return packet; thereby mitigating IP source address spoofing.

Description

A compromised host in an enclave can be used by a malicious platform to launch cyberattacks on third parties. This is a common practice in "botnets", which are a collection of compromised computers using malware to attack other computers or networks. DDoS attacks frequently leverage IP source address spoofing to send packets to multiple hosts that in turn will then send return traffic to the hosts with the IP addresses that were forged. This can generate significant amounts of traffic. Therefore, protection measures to counteract IP source address spoofing must be taken. When uRPF is enabled in strict mode, the packet must be received on the interface that the device would use to forward the return packet; thereby mitigating IP source address spoofing.

STIG	Date
Cisco IOS XR Router RTR Security Technical Implementation Guide	2020-09-23

Details

Check Text ( C-18235r288855_chk )
This requirement is not applicable for the DODIN Backbone. Review the router configuration to verify uRPF or an egress ACL has been configured on all internal interfaces to restrict the router from accepting outbound IP packets that contain an illegitimate address in the source address field. uRPF example interface GigabitEthernet0/0/0/1 description downstream link to LAN ipv4 address 10.1.34.3 255.255.255.0 ipv4 verify unicast source reachable-via rx Egress ACL example ipv4 access-list EGRESS_FILTER 10 permit udp 10.1.15.0 0.0.0.255 any eq domain 20 permit tcp 10.1.15.0 0.0.0.255 any eq ftp 30 permit tcp 10.1.15.0 0.0.0.255 any eq ftp-data 40 permit tcp 10.1.15.0 0.0.0.255 any eq www 50 permit icmp 10.1.15.0 0.0.0.255 any 60 permit icmp 10.1.15.0 0.0.0.255 any echo 70 deny ipv4 any any … … … interface GigabitEthernet0/0/0/1 description downstream link to LAN ipv4 address 10.1.34.3 255.255.255.0 ipv4 access-group EGRESS_FILTER ingress If uRPF or an egress ACL to restrict the router from accepting outbound IP packets that contain an illegitimate address in the source address field has not been configured on all internal interfaces in an enclave, this is a finding.

Check Text ( C-18235r288855_chk )

This requirement is not applicable for the DODIN Backbone.

Review the router configuration to verify uRPF or an egress ACL has been configured on all internal interfaces to restrict the router from accepting outbound IP packets that contain an illegitimate address in the source address field.

uRPF example

interface GigabitEthernet0/0/0/1
description downstream link to LAN
ipv4 address 10.1.34.3 255.255.255.0
ipv4 verify unicast source reachable-via rx

Egress ACL example

ipv4 access-list EGRESS_FILTER
10 permit udp 10.1.15.0 0.0.0.255 any eq domain
20 permit tcp 10.1.15.0 0.0.0.255 any eq ftp
30 permit tcp 10.1.15.0 0.0.0.255 any eq ftp-data
40 permit tcp 10.1.15.0 0.0.0.255 any eq www
50 permit icmp 10.1.15.0 0.0.0.255 any
60 permit icmp 10.1.15.0 0.0.0.255 any echo
70 deny ipv4 any any
…
…
…
interface GigabitEthernet0/0/0/1
description downstream link to LAN
ipv4 address 10.1.34.3 255.255.255.0
ipv4 access-group EGRESS_FILTER ingress

If uRPF or an egress ACL to restrict the router from accepting outbound IP packets that contain an illegitimate address in the source address field has not been configured on all internal interfaces in an enclave, this is a finding.

Fix Text (F-18233r288856_fix)
This requirement is not applicable for the DODIN Backbone. Configure the router to ensure that an egress ACL or uRPF is configured on internal interfaces to restrict the router from accepting any outbound IP packet that contains an illegitimate address in the source field. The example below enables uRPF. RP/0/0/CPU0:R3(config)#int g0/0/0/1 RP/0/0/CPU0:R3(config-if)#ipv4 verify unicast source reachable-via rx

Fix Text (F-18233r288856_fix)

This requirement is not applicable for the DODIN Backbone.

Configure the router to ensure that an egress ACL or uRPF is configured on internal interfaces to restrict the router from accepting any outbound IP packet that contains an illegitimate address in the source field. The example below enables uRPF.

RP/0/0/CPU0:R3(config)#int g0/0/0/1
RP/0/0/CPU0:R3(config-if)#ipv4 verify unicast source reachable-via rx