The Dell OS10 Switch must have all user-facing or untrusted ports configured as access switch ports.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-269970	SRG-NET-000512-L2S-000011	OS10-L2S-000250	SV-269970r1052296_rule	2024-12-11	1

Description
Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim's MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker's VLAN ID (probably the well-known and omnipresent default VLAN) is stripped off by the switch, and the inner tag that will have the victim's VLAN ID is used by the switch as the next hop and sent out the trunk port.

Description

Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim's MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker's VLAN ID (probably the well-known and omnipresent default VLAN) is stripped off by the switch, and the inner tag that will have the victim's VLAN ID is used by the switch as the next hop and sent out the trunk port.

ℹ️ Check
Review the Dell OS10 Switch configurations and examine all user-facing or untrusted switch ports. The example below shows both trunk port and user-facing access ports: interface ethernet 1/1/1 no shutdown switchport mode trunk switchport access vlan 99 switchport trunk allowed vlan 2100-2102 ! interface ethernet1/1/2 no shutdown switchport access vlan 201 flowcontrol receive off ! interface ethernet1/1/3 no shutdown switchport access vlan 200 flowcontrol receive off Note: The default switchport mode is access, so it will not be displayed when viewing the configuration of the user-facing ports. If any of the user-facing switch ports are configured as a trunk, this is a finding.

ℹ️ Check

Review the Dell OS10 Switch configurations and examine all user-facing or untrusted switch ports. The example below shows both trunk port and user-facing access ports: interface ethernet 1/1/1 no shutdown switchport mode trunk switchport access vlan 99 switchport trunk allowed vlan 2100-2102 ! interface ethernet1/1/2 no shutdown switchport access vlan 201 flowcontrol receive off ! interface ethernet1/1/3 no shutdown switchport access vlan 200 flowcontrol receive off Note: The default switchport mode is access, so it will not be displayed when viewing the configuration of the user-facing ports. If any of the user-facing switch ports are configured as a trunk, this is a finding.

✔️ Fix
Disable trunking on all user-facing or untrusted switch ports: OS10(conf-if-eth1/1/1)# interface ethernet 1/1/2 OS10(conf-if-eth1/1/2)# switchport mode access OS10(conf-if-eth1/1/2)# switchport access vlan 201