V-221091

Discussion

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.

Check Content

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

uRPF example

interface Ethernet2/4
 description downstream link to LAN
 no switchport
 ip address 10.1.12.1/24
 ip verify unicast source reachable-via rx

Egress ACL example

ip access-list EGRESS_FILTER
 10 permit udp 10.1.15.0/24 any eq domain 
 20 permit tcp 10.1.15.0/24 any eq ftp 
 30 permit tcp 10.1.15.0/24 any eq ftp-data 
 40 permit tcp 10.1.15.0/24 any eq www 
 50 permit icmp 10.1.15.0/24 any 
 60 permit icmp 10.1.15.0/24 any echo 
 70 deny ip any any
…
…
…
interface Ethernet2/4
 description downstream link to LAN
 no switchport
 ip access-group EGRESS_FILTER in
 ip address 10.1.12.1/24

If uRPF or an egress ACL to restrict the switch 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.