The F5 BIG-IP appliance must be configured to restrict itself from accepting outbound packets that contain an illegitimate address in the source address field via an egress filter or by enabling Unicast Reverse Path Forwarding (uRPF).

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-266259	SRG-NET-000364-FW-000042	F5BI-FW-300015	SV-266259r1024876_rule	2024-09-09	1

Description
A compromised host in an enclave can be used by a malicious platform to launch cyber attacks 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. Distributed denial-of-service (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. F5 BIG-IP AFM Source checking: When source checking is enabled, the BIG-IP system verifies that the return path for an initial packet is through the same VLAN from which the packet originated. Note that the system only enables source checking if the global setting Auto Last Hop is disabled.

Description

A compromised host in an enclave can be used by a malicious platform to launch cyber attacks 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. Distributed denial-of-service (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. F5 BIG-IP AFM Source checking: When source checking is enabled, the BIG-IP system verifies that the return path for an initial packet is through the same VLAN from which the packet originated. Note that the system only enables source checking if the global setting Auto Last Hop is disabled.

ℹ️ Check
From the BIG-IP GUI: 1. Network. 2. VLANs. 3. VLAN List. 4. <Name> of internal VLAN. 5. Verify that "Source Check" is enabled. 6. Verify that Auto Last Hop is set to "Disabled". From the BIG-IP Console, type the following command(s): tmsh list net vlan <Name> auto-lasthop tmsh list net vlan <Name> source-checking If the BIG-IP appliance is not configured to disable Auto Last Hop, this is a finding.

ℹ️ Check

From the BIG-IP GUI: 1. Network. 2. VLANs. 3. VLAN List. 4. <Name> of internal VLAN. 5. Verify that "Source Check" is enabled. 6. Verify that Auto Last Hop is set to "Disabled". From the BIG-IP Console, type the following command(s): tmsh list net vlan <Name> auto-lasthop tmsh list net vlan <Name> source-checking If the BIG-IP appliance is not configured to disable Auto Last Hop, this is a finding.

✔️ Fix
From the BIG-IP GUI: 1. Network. 2. VLANs. 3. VLAN List. 4. <Name> of internal VLAN. 5. Check the box next to "Source Check". 6. Set Auto Last Hop to "Disabled". From the BIG-IP Console, type the following command(s): tmsh modify net vlan <Name> auto-lasthop disabled tmsh list net vlan <Name> source-checking enabled tmsh save sys config