The Cisco ASA VPN remote access server must be configured to disable split-tunneling for remote clients.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-239982	CASA-VN-000700	SV-239982r929016_rule		Medium

Description
Split tunneling would in effect allow unauthorized external connections, making the system more vulnerable to attack and to exfiltration of organizational information. A VPN hardware or software client with split tunneling enabled provides an unsecured backdoor to the enclave from the internet. With split tunneling enabled, a remote client has access to the internet while at the same time has established a secured path to the enclave via an IPsec tunnel. A remote client connected to the internet that has been compromised by an attacker in the internet provides an attack base to the enclave’s private network via the IPsec tunnel. Hence, it is imperative that the VPN gateway enforces a no split-tunneling policy to all remote clients.

Description

Split tunneling would in effect allow unauthorized external connections, making the system more vulnerable to attack and to exfiltration of organizational information. A VPN hardware or software client with split tunneling enabled provides an unsecured backdoor to the enclave from the internet. With split tunneling enabled, a remote client has access to the internet while at the same time has established a secured path to the enclave via an IPsec tunnel. A remote client connected to the internet that has been compromised by an attacker in the internet provides an attack base to the enclave’s private network via the IPsec tunnel. Hence, it is imperative that the VPN gateway enforces a no split-tunneling policy to all remote clients.

STIG	Date
Cisco ASA VPN Security Technical Implementation Guide	2023-09-14

Details

Check Text ( C-43215r929015_chk )
Verify the ASA disables split-tunneling for remote clients VPNs as shown in the example below. group-policy ANY_CONNECT_GROUP attributes … … … split-tunnel-policy tunnelall If the ASA does not disable split-tunneling for remote clients VPNs, this is a finding. Note: Certain cloud products require direct connectivity to operate correctly. These items may be excluded from the split tunneling restriction if documented and approved. If split-tunneling for remote client VPNs is enabled by the above exception, verify only authorized external destinations are excluded from tunneling as shown in the example below: Webvpn anyconnect-custom-attr dynamic-split-exclude-domains description DoD IL5 Authorized Destinations anyconnect-custom-data dynamic-split-exclude-domains DoD-IL5 dod.teams.microsoft.us,azureedge.net,core.usgovcloudapi.net,streaming.media.usgovcloudapi.net,wvd.azure.us,cdn.office365.us anyconnect-custom dynamic-split-exclude-domains value DoD-IL5 If any unauthorized exempted connections exist, this is a finding.

Check Text ( C-43215r929015_chk )

Verify the ASA disables split-tunneling for remote clients VPNs as shown in the example below.

group-policy ANY_CONNECT_GROUP attributes
…
…
…
split-tunnel-policy tunnelall

If the ASA does not disable split-tunneling for remote clients VPNs, this is a finding.

Note: Certain cloud products require direct connectivity to operate correctly. These items may be excluded from the split tunneling restriction if documented and approved.

If split-tunneling for remote client VPNs is enabled by the above exception, verify only authorized external destinations are excluded from tunneling as shown in the example below:

Webvpn
anyconnect-custom-attr dynamic-split-exclude-domains description DoD IL5 Authorized Destinations
anyconnect-custom-data dynamic-split-exclude-domains DoD-IL5 dod.teams.microsoft.us,azureedge.net,core.usgovcloudapi.net,streaming.media.usgovcloudapi.net,wvd.azure.us,cdn.office365.us

anyconnect-custom dynamic-split-exclude-domains value DoD-IL5

If any unauthorized exempted connections exist, this is a finding.

Fix Text (F-43174r666351_fix)
Configure the ASA to disable split-tunneling for remote clients VPNs as shown in the example below. ASA2(config)# group-policy ANY_CONNECT_GROUP attributes ASA2(config-group-policy)# split-tunnel-policy tunnelall ASA2(config-group-policy)# end