Practice SC.L2-3.13.7 Details

Source of Reference: The official CMMC Level 2 Assessment Guide from the Office of the Under Secretary of Defense Acquisition & Sustainment.

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SC.L2-3.13.7 – SPLIT TUNNELING

SECURITY REQUIREMENT

Prevent remote devices from simultaneously establishing non-remote connections with organizational systems and communicating via some other connection to resources in external networks (i.e., split tunneling).

ASSESSMENT OBJECTIVES

Determine if:

[a] remote devices are prevented from simultaneously establishing non-remote connections with the system and communicating via some other connection to resources in external networks (i.e., split tunneling).

POTENTIAL ASSESSMENT METHODS AND OBJECTS

Examine

[SELECT FROM: System and communications protection policy;procedures addressing boundary protection; system security plan; system design documentation; system hardware and software; system architecture; system configuration settings and associated documentation; system audit logs and records; other relevant documents or records].

Interview

[SELECT FROM: System or network administrators; personnel with information security responsibilities; system developer; personnel with boundary protection responsibilities].

Test

[SELECT FROM: Mechanisms implementing boundary protection capability; mechanisms supporting or restricting non-remote connections].

DISCUSSION

Split tunneling might be desirable by remote users to communicate with local system resources such as printers or file servers. However, split tunneling allows unauthorized external connections, making the system more vulnerable to attack and to exfiltration of organizational information.This requirement is implemented in remote devices (e.g., notebook computers, smart phones, and tablets) through configuration settings to disable split tunneling in those devices, and by preventing configuration settings from being readily configurable by users. This requirement is implemented in the system by the detection of split tunneling (or of configuration settings that allow split tunneling) in the remote device, and by prohibiting the connection if the remote device is using split tunneling.

FURTHER DISCUSSION

Split tunneling for a remote user utilizes two connections: accessing resources on the internal network via a VPN and simultaneously accessing an external network such as a public network or the internet.

Split tunneling presents a potential opportunity where an open unencrypted connection from a public network could allow an adversary to access resources on internal network. As a mitigation strategy, the split tunneling setting should be disabled on all devices so that all traffic, including traffic for external networks or the internet, goes through the VPN.

Example

You are a system administrator responsible for configuring the network to prevent remote users from using split tunneling. You review the configuration of remote user laptops. You discover that remote users are able to access files, email, database and other services through the VPN connection while also being able to print and access resources on their local network. You change the configuration settings for all company computers to disable split tunneling [a]. You test a laptop that has had the new hardening procedures applied and verify that all traffic from the laptop is now routed through the VPN connection.

Potential Assessment Considerations

• Does the system prevent remote devices that have established connections (e.g., remote laptops) with the system from communicating outside that communications path with resources on uncontrolled/unauthorized networks [a]?

KEY REFERENCES

• NIST SP 800-171 Rev 2 3.13.7