The NSX Tier-0 Gateway router must be configured to have Internet Control Message Protocol (ICMP) mask replies disabled on all external interfaces.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-265442	SRG-NET-000362-RTR-000114	NT0R-4X-000065	SV-265442r999916_rule	2024-12-13	1

Description
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Mask Reply ICMP messages are commonly used by attackers for network mapping and diagnosis.

ℹ️ Check
If the Tier-0 Gateway is deployed in an Active/Active HA mode, this is Not Applicable. From the NSX Manager web interface, go to Security >> Policy Management >> Gateway Firewall >> Gateway Specific Rules, and choose each Tier-0 Gateway in the drop-down menu. Review each Tier-0 Gateway Firewall rule to verify one exists to drop ICMP mask replies. If a rule does not exist to drop ICMP mask replies, this is a finding.

ℹ️ Check

If the Tier-0 Gateway is deployed in an Active/Active HA mode, this is Not Applicable. From the NSX Manager web interface, go to Security >> Policy Management >> Gateway Firewall >> Gateway Specific Rules, and choose each Tier-0 Gateway in the drop-down menu. Review each Tier-0 Gateway Firewall rule to verify one exists to drop ICMP mask replies. If a rule does not exist to drop ICMP mask replies, this is a finding.

✔️ Fix
To configure a shared rule to drop ICMP unreachable messages, do the following: From the NSX Manager web interface, go to Security >> Policy Management >> Gateway Firewall >> All Shared Rules. Click "Add Rule" (add a policy first if needed). Under "Services", select the custom service that identifies ICMP mask replies, and then click "Apply". Enable logging, under the "Applied To" field select the target Tier-0 gateways' external interfaces, and then select "Publish" to enforce the new rule. Note: A rule can also be created under Gateway Specific Rules to meet this requirement. Note: A pre-created service for ICMP mask replies does not exist by default and may need created.

✔️ Fix

To configure a shared rule to drop ICMP unreachable messages, do the following: From the NSX Manager web interface, go to Security >> Policy Management >> Gateway Firewall >> All Shared Rules. Click "Add Rule" (add a policy first if needed). Under "Services", select the custom service that identifies ICMP mask replies, and then click "Apply". Enable logging, under the "Applied To" field select the target Tier-0 gateways' external interfaces, and then select "Publish" to enforce the new rule. Note: A rule can also be created under Gateway Specific Rules to meet this requirement. Note: A pre-created service for ICMP mask replies does not exist by default and may need created.