03.13.09: Network Disconnect

03.13.09 sits in the NIST SP 800-171 security requirements that federal contractors and other nonfederal organizations follow to protect Controlled Unclassified Information (CUI). The control is deceptively simple: end the network connection when the session is over. In practice, teams stumble because “session over” varies by system, remote access method, and business process, and because the evidence is often scattered across firewall configs, VPN profiles, application settings, and endpoint policies.

For a CCO, CISO, or GRC lead, the fastest path is to treat 03.13.09 as an engineering requirement with clear acceptance criteria. Decide what events require a network disconnect, standardize settings across common connection types, and document exceptions where technical limits or mission needs block strict settings. Then validate it the way an assessor will: show the configuration, demonstrate behavior, and prove it stays enforced over time.

This page gives requirement-level implementation guidance you can hand to network, endpoint, and application owners to implement quickly, with the artifacts you need to keep for assessment readiness under NIST SP 800-171 Rev. 3. (NIST SP 800-171 Rev. 3)

Regulatory text

Requirement: “NIST SP 800-171 Rev. 3 requirement 03.13.09 (Network Disconnect).” (NIST SP 800-171 Rev. 3)

Operator interpretation (what you must accomplish)

You must implement technical controls that terminate or logically disconnect network sessions when the session ends or when defined disconnect conditions occur (for example, user logoff, session timeout, or explicit termination). The goal is to prevent an attacker or unauthorized user from reusing an abandoned connection to access systems that store, process, or transmit CUI. (NIST SP 800-171 Rev. 3)

What an assessor expects to see

• A documented standard for disconnect behavior (what triggers disconnect, where it applies).
• Implemented configurations on in-scope systems and access paths.
• Test evidence that shows the disconnect occurs as designed.
• Exception handling where a disconnect cannot be enforced, with compensating controls and approvals.

Plain-English interpretation of the requirement

If a user is “done,” the network path they used to reach CUI must not remain open. That includes remote access, admin sessions, and interactive application sessions. You are controlling session persistence and reducing the window for session hijacking, unauthorized reuse, and lateral movement from unattended endpoints.

Treat “network disconnect” as broader than a cable unplug. It includes:

• VPN tunnels ending when a user disconnects or after idle time
• SSH/RDP sessions terminating after logoff/idle time
• VDI sessions ending cleanly and not leaving active transport connections behind
• Web sessions ending with session expiration plus termination of underlying access where applicable (for example, reverse proxy timeouts)

Who it applies to (entity and operational context)

Entities

• Federal contractors and subcontractors handling CUI in nonfederal systems. (NIST SP 800-171 Rev. 3)
• Any nonfederal organization that must meet NIST SP 800-171 requirements by contract flow-down or customer requirement. (NIST SP 800-171 Rev. 3)

Operational context (where this control shows up)

• Remote access into the CUI enclave: VPN, ZTNA, VDI, bastion hosts
• Privileged administration paths: jump boxes, RDP, SSH, management consoles
• User-facing applications that expose CUI: internal web apps, file shares, collaboration tools
• Third-party managed environments when the third party operates the network boundary or identity/session layer

What you actually need to do (step-by-step)

Step 1: Define scope and “session types” for CUI access

Create a short inventory of access paths into CUI systems:

• User remote access (VPN/ZTNA/VDI)
• Admin remote access (RDP/SSH to servers, hypervisor consoles)
• App sessions (web apps, SaaS portals used for CUI)
• Network file access (SMB/NFS via corporate network or remote)

For each, identify the enforcing control plane: firewall/VPN concentrator, identity provider, reverse proxy, endpoint policy, application config, or managed service.

Deliverable: “03.13.09 Session Map” table (system/access method/owner/enforcement point).

Step 2: Set disconnect requirements you can test

Write a standard that answers:

• What events end a session (logoff, application logout, closing client, network loss)?
• What conditions force termination (idle, absolute session lifetime, token expiration, admin termination)?
• Where must this be enforced (all remote access, all privileged admin sessions, all CUI apps)?

Avoid vague wording like “disconnect when appropriate.” Make it measurable: “Connection terminates upon logout and after inactivity per standard.”

Deliverable: Network/session disconnect standard (1–2 pages) owned by security engineering and approved through your policy process.

Step 3: Implement technical enforcement by access type

Use centralized enforcement first, then fill gaps.

A. VPN / ZTNA

• Configure idle timeout and maximum session duration.
• Ensure logout terminates tunnel and clears session state.
• Disable “always-on” behavior for users who do not need it for CUI, or document why it remains and how risk is handled.

B. RDP / SSH / privileged admin

• Enforce idle disconnect and session termination settings on jump hosts and target servers.
• Ensure “disconnected sessions” do not remain indefinitely (common with RDP).
• Align privileged access workflows so admins must re-authenticate after disconnect.

C. VDI / remote application platforms

• Configure session limits and disconnect behavior at the broker/gateway.
• Ensure a user closing a client results in session termination (or rapid expiration) rather than leaving an active session running.

D. Web applications handling CUI

• Implement server-side session expiration (idle and absolute).
• Rotate/expire tokens; prevent long-lived sessions by default.
• Align reverse proxy and load balancer timeouts to application session limits so transport connections do not linger beyond session validity.

E. Network file services

• Enforce SMB session timeouts where feasible.
• Confirm endpoints lock and re-auth where required by your broader access controls; for 03.13.09, focus on the network session itself.

Deliverable: Configuration records (screenshots/exports) per enforcing system.

Step 4: Validate with repeatable tests (make it assessor-friendly)

For each session type, create a simple test script:

• Establish session to in-scope resource
• Perform “end of session” action (logout/close client) and confirm disconnect
• Wait through configured idle condition and confirm disconnect triggers
• Attempt to reuse the session without re-authentication and confirm it fails

Record evidence as:

• Date/time, system tested, tester, expected behavior, actual result
• Supporting logs (VPN log, RDP gateway log, IdP session log, app audit log)

Deliverable: “03.13.09 Network Disconnect Test Results” with supporting logs.

Step 5: Document exceptions and compensating controls

Some systems cannot enforce clean disconnect (legacy OT, specialized applications, third-party hosted tools). Treat exceptions as controlled risk:

• Document technical limitation and impacted CUI flow
• Define compensating controls (for example, access restricted to jump host with enforced disconnect; enhanced monitoring; stricter MFA re-auth)
• Assign an owner and review cadence
• Keep written approval

Deliverable: Exception register entries mapped to 03.13.09.

Step 6: Operationalize ongoing assurance

Add recurring checks:

• Quarterly config review for VPN/remote access profiles
• Monthly spot-check tests for a sample of access methods
• Alerting for unusually long sessions where your tools support it
• Change management requirement: any new CUI app must declare session/disconnect settings

This is where Daydream fits naturally: track the control requirement, assign system owners, collect configs and test evidence on a schedule, and keep 03.13.09 artifacts packaged for assessment requests without scrambling.

Required evidence and artifacts to retain

Keep evidence in a form that survives staff turnover and tool changes.

Artifact	What it proves	Owner
Network/session disconnect standard	Defined disconnect triggers and scope	GRC + Security Engineering
Session Map (systems and access paths)	You identified where disconnect must be enforced	GRC
Config exports/screenshots (VPN, gateways, brokers, proxies, apps)	Control is implemented, not just written	Network/App/Endpoint owners
Test scripts and test results	Control works in practice	Security Engineering / IT
Logs showing disconnect events	Disconnect actually occurs	SOC / IT
Exceptions + approvals + compensating controls	You manage constraints intentionally	GRC + Risk owner
Change tickets for config changes	Governance and traceability	ITSM owners

Common exam/audit questions and hangups

• “Show me where 03.13.09 is enforced for remote access.” Have VPN/ZTNA profiles exported and mapped to in-scope user groups. (NIST SP 800-171 Rev. 3)
• “How do you know sessions terminate?” Provide a test record plus log excerpts for disconnect events.
• “What about RDP ‘disconnected’ sessions?” Assessors often focus on whether sessions persist after closing the window; show the setting that terminates them.
• “Do your web apps expire sessions server-side?” A client-side timeout banner is not enough; show server session/token expiration configuration and proxy alignment.
• “How do you handle exceptions?” Produce approved exceptions with compensating controls and review notes.

Frequent implementation mistakes and how to avoid them

1. Policy-only compliance. Teams write a standard but cannot show enforcement. Fix: tie every statement to a configuration and a test.
2. Timeout mismatch across layers. App session expires at one interval, reverse proxy stays open longer. Fix: align timeouts and document the chosen hierarchy.
3. Relying on endpoint screen lock as “disconnect.” Screen lock helps, but 03.13.09 expects network session termination. Fix: configure server/gateway session termination in addition to endpoint controls.
4. Ignoring third-party managed components. If a third party operates your VDI broker or VPN, you still need evidence. Fix: require config attestations and logs in contract deliverables.
5. No exception discipline. Legacy systems become permanent gaps. Fix: time-bound exceptions with an owner and a roadmap item.

Enforcement context and risk implications

No public enforcement sources were provided for this requirement in the source catalog, so this page does not cite specific cases.

Operationally, weak disconnect controls increase the likelihood that abandoned sessions remain usable. That creates avoidable exposure for CUI environments: unauthorized reuse from unattended devices, persistence for an intruder who gains local access, and broader blast radius after credential theft. In assessments, the most common failure mode is evidence: teams cannot show consistent enforcement across the different ways users reach CUI.

A practical 30/60/90-day execution plan

First 30 days (establish control and cover the highest-risk paths)

• Build the Session Map for CUI access paths and owners.
• Publish the disconnect standard with defined triggers and exception process.
• Implement and document disconnect settings for VPN/ZTNA and privileged access gateways first.
• Run initial validation tests for remote access and privileged admin.

Days 31–60 (expand coverage and make evidence repeatable)

• Extend enforcement to VDI brokers/gateways and core CUI web applications.
• Align proxy/load balancer timeouts with application session expiration.
• Centralize evidence storage (configs, exports, logs, tests) with clear naming tied to 03.13.09.
• Open exception requests for systems that cannot meet the standard, with compensating controls.

Days 61–90 (operationalize and prepare for assessment scrutiny)

• Add recurring config review and spot-check tests to your control calendar.
• Integrate disconnect requirements into change management for new CUI apps and new remote access groups.
• Perform a tabletop “assessor request drill”: produce the standard, configs, and test results within a business day.
• Use Daydream (or your GRC system) to assign control owners and automate evidence collection reminders so artifacts stay current.

Frequently Asked Questions

Does 03.13.09 require a specific timeout value?

NIST SP 800-171 Rev. 3 does not provide a specific number in the provided excerpt, so set a value based on your risk and operational needs and make it consistent and testable. Document the rationale and enforce it across in-scope access paths. (NIST SP 800-171 Rev. 3)

Is a workstation screen lock enough to satisfy network disconnect?

Screen lock helps protect an endpoint, but 03.13.09 is about terminating the network connection or session. Configure disconnect at the VPN/gateway/server/application layer and keep test evidence that the session cannot be reused without re-authentication. (NIST SP 800-171 Rev. 3)

How do we handle SaaS applications where we can’t control session mechanics?

Treat it as shared responsibility: configure what the SaaS allows (session duration, idle timeout, token policies) and document vendor-provided settings or attestations. If settings are insufficient for CUI use, document an exception and add compensating controls such as access through a controlled proxy or restricted user groups.

What systems should we test first to show meaningful compliance?

Start with the paths most likely to be used for unauthorized persistence: VPN/ZTNA remote access and privileged admin access (RDP/SSH via jump hosts). Then test VDI and primary CUI applications that users access daily.

What evidence is strongest for auditors?

Config exports plus a repeatable test record, backed by logs showing disconnect events, is stronger than screenshots alone. Keep the artifacts mapped to the 03.13.09 requirement so you can produce them quickly. (NIST SP 800-171 Rev. 3)

How do third parties fit into 03.13.09?

If a third party provides or operates part of the access path (managed VPN, hosted VDI, managed bastion), require configuration evidence and operational logs as part of due diligence and ongoing monitoring. Your assessment still needs proof that disconnect controls exist and operate for CUI access.