SC-7(9): Restrict Threatening Outgoing Communications Traffic

This control enhancement sits inside the NIST SP 800-53 boundary protection family (SC-7) and focuses on a specific failure mode: your systems can become the source of harm to others. Examiners read SC-7(9) as an expectation that you treat outbound traffic as enforceable policy, not an afterthought behind inbound firewalling.

Practically, this requirement forces two design decisions. First, you must define what “threatening outgoing communications traffic” means for your mission and architecture. Second, you must implement technical controls that can both detect and deny those communications, with a process that proves the block action is intentional, reviewed, and repeatable.

If you run federal information systems or contractor systems handling federal data, you’ll see SC-7(9) show up in authorization packages, continuous monitoring, and incident response discussions, especially where EDR, DNS security, web proxies, email security, and cloud egress controls overlap. Your fastest path to implementation is to anchor the control in egress choke points, route “unknown” egress through inspection, and document how you tune and override blocks without creating silent backdoors.

Regulatory text

Requirement (excerpt): “Detect and deny outgoing communications traffic posing a threat to external systems; and” ¹

Operator interpretation: you must (1) detect outbound traffic patterns or destinations that indicate your environment is attacking, exploiting, scanning, spamming, exfiltrating, or participating in botnet activity against external systems, and (2) deny that traffic through an enforcement mechanism (block, sinkhole, quarantine, or equivalent) rather than only generating alerts. The control is written as an action requirement: detection alone does not satisfy it ².

Plain-English interpretation (what “threatening egress” looks like)

Threatening outgoing communications typically includes:

• Known-bad destinations: command-and-control domains, malware distribution hosts, phishing kits, TOR exit coordination endpoints, known scanner infrastructures.
• Malicious patterns: high-rate connection attempts across ports/hosts, repeated authentication sprays outbound to third parties, abnormal SMTP bursts, suspicious DNS beacons, encrypted outbound sessions to rare domains from non-browser processes.
• Compromised asset behavior: an endpoint or workload contacting many external IPs, or repeatedly failing connections in a way consistent with scanning or worm propagation.

Your program needs a written definition plus a technical implementation that can stop these flows in real time or near real time, with a clear owner and exception path.

Who it applies to (entity + operational context)

Entity types in scope: federal information systems and contractor systems handling federal data ¹.

Operational context where SC-7(9) is usually assessed:

• Enterprise perimeter and internet egress: NAT gateways, firewalls, secure web gateways, DNS resolvers.
• Cloud environments: VPC/VNet egress, cloud NAT, egress firewalls, workload security controls.
• Remote endpoints: laptops off-network using VPN, ZTNA, or roaming web/DNS protection.
• Email and messaging: outbound SMTP and API-based email sending services, where compromise can harm others.
• Third-party operated components you manage: hosted applications, managed endpoints, or SaaS integrations where you control configuration and can enforce egress policies.

If you can’t control a given egress path (for example, a third party’s internal network), treat it as a third-party risk problem: contract for telemetry and blocking capabilities, or redesign the integration so your controlled egress points mediate traffic.

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

1) Assign ownership and define scope boundaries

• Name a control owner (often Network Security or SecOps) and a policy owner (often Security Governance/GRC).
• Document in-scope egress paths: corporate offices, data centers, cloud accounts/projects, developer networks, remote user stacks, and any direct-to-internet exceptions.
• Identify authoritative choke points where you can enforce deny actions: NGFW, SWG/proxy, DNS filtering, CASB, cloud egress firewall, EDR network containment.

Deliverable: a one-page “SC-7(9) egress enforcement scope” appendix tied to your system boundary documentation.

2) Write an operational definition of “threatening outgoing traffic”

Create a short standard with:

• Threat categories (examples: known malicious destination, scanning behavior, exploit traffic, spam/phishing distribution, botnet beaconing).
• Detection sources you will accept (threat intel feeds, DNS reputation, EDR detections, IDS signatures, UEBA anomalies).
• Default action per category (block, sinkhole, quarantine host, rate-limit, or manual approval).

Keep this tight. Auditors want to see that your deny decisions are policy-driven, not ad hoc.

3) Instrument detection at the right layers (network + endpoint)

Minimum coverage pattern:

• DNS layer: block/sinkhole known malicious domains and newly observed suspicious domains.
• Web layer (HTTP/S): proxy/SWG policies to block malware/phishing infrastructure and suspicious categories; inspect where permissible.
• Network layer: egress firewall rules plus IDS/IPS detections tuned for outbound scanning and exploit attempts.
• Endpoint/workload layer: EDR detections for beaconing, suspicious processes initiating network connections, and host isolation triggers.

Design tip: pick at least one layer that can still block traffic when users are off VPN (roaming DNS/SWG or EDR containment).

4) Implement deny controls with safe failure modes

• Configure enforcement so it cannot silently degrade into “alert-only” without change control.
• Ensure logs capture the block decision: source asset identity, user (if available), destination, detection reason/rule, timestamp, and action taken.
• Define fail-open vs fail-closed behavior for each enforcement point. If you choose fail-open for operational continuity, document compensating controls and the monitoring you use to catch gaps.

5) Build an exception and tuning workflow that does not weaken the control

Create a workflow that:

• Requires a ticket for allow-listing with business justification, scope (source/destination), expiration, and approval.
• Forces time-bounded exceptions with review.
• Captures tuning decisions (false positives, rule thresholds, intel feed changes) with evidence.

This is where many programs fail: permanent allow-lists accumulate and become the real policy.

6) Operationalize response: blocking must connect to IR

When a block indicates probable compromise:

• Open an incident or security case.
• Triage asset posture: recent EDR alerts, new software, suspicious persistence, outbound volume changes.
• If needed, isolate the host/workload, rotate credentials, and validate no other assets show the same egress pattern.

7) Continuous monitoring and periodic validation

• Run a recurring review of top blocked destinations, top blocked sources, and exception lists.
• Validate that each in-scope egress path still routes through enforcement (network changes and cloud projects drift).
• Test detection and deny in controlled ways (for example, using benign test domains or vendor-provided test indicators) and retain results.

Required evidence and artifacts to retain

Keep evidence that proves both design and operating effectiveness:

Governance

• SC-7(9) control statement mapped to owner, scope, and enforcement points.
• “Threatening egress” definition standard and exception procedure.
• Change management records for enforcement policy changes.

Technical configuration

• Firewall/proxy/DNS/EDR policy exports or screenshots showing deny rules and categories.
• Threat intel feed configuration references (what feeds, where applied).

Operational records

• Block logs (sample sets) showing action = deny/sinkhole/quarantine and reason codes.
• Incident/ticket records tied to significant outbound blocks.
• Exception tickets with approvals and expiration reviews.
• Periodic review/tuning notes (what changed, why, who approved).

Tip for speed: set an evidence cadence (monthly snapshots plus event-driven captures for significant changes) and automate collection where possible. Daydream is commonly used here to map SC-7(9) to the owner, implementation procedure, and recurring evidence artifacts so audits don’t turn into log archaeology ¹.

Common exam/audit questions and hangups

Auditors and assessors repeatedly ask:

• “Show me where you deny outbound malicious traffic.” They want to see enforcement points and policy objects, not architecture diagrams.
• “How do you know remote devices are covered?” If laptops can go direct-to-internet, they’ll press on roaming controls.
• “What’s your exception process?” They look for time bounds, approvals, and periodic reviews.
• “How do you distinguish exfiltration controls from ‘threatening traffic’?” Be ready to explain that SC-7(9) includes outbound harm to others, not only data loss.

Hangup: teams provide inbound IPS evidence and assume it carries. This enhancement is explicitly outbound-focused ².

Frequent implementation mistakes (and how to avoid them)

1. Alert-only detections.
   Fix: ensure the same detection that generates the alert also triggers a deny action at some layer, or document the automated workflow that blocks within the required operational window.

2. Too many direct egress paths.
   Fix: reduce and standardize egress points. In cloud, route through centralized egress controls. For remote endpoints, use roaming DNS/SWG or endpoint containment.

3. Allow-lists that never expire.
   Fix: require expiration on exceptions and review the exception list on a fixed cadence.

4. No proof that the deny action happened.
   Fix: tune logging and retention so a reviewer can trace “detection → deny → ticket/IR.”

5. Third-party blind spots.
   Fix: contract for outbound security telemetry and blocking controls, or keep integrations behind your controlled gateways.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not cite enforcement actions. Practically, SC-7(9) is assessed as a control that reduces downstream harm: if your environment participates in attacks against others, you risk incident escalation, contract findings, loss of trust, and broader regulatory scrutiny tied to incident handling and system authorization ².

A practical 30/60/90-day execution plan

First 30 days (establish enforceable scope)

• Assign control owner and document in-scope egress paths and enforcement points.
• Publish the “threatening egress” definition and exception workflow.
• Turn on baseline deny controls for known-bad destinations at DNS and SWG/proxy layers where available.
• Start evidence capture: policy exports, example deny logs, and the exception register.

Days 31–60 (close coverage gaps and connect to IR)

• Cover remote endpoints with roaming DNS/SWG or EDR network containment policies.
• Add outbound scanning/exploit detections at IDS/IPS or EDR behavioral layer.
• Integrate block events into SIEM/SOAR with ticket creation for high-confidence threats.
• Run a tabletop: “Outbound C2 beacon detected and blocked,” and record actions and outcomes.

Days 61–90 (prove operational maturity)

• Validate egress routing across network and cloud changes; document results.
• Tighten exception governance: expirations, reviews, and metrics you track (qualitative is fine).
• Perform a controlled test of deny actions and keep artifacts.
• Implement recurring evidence collection in Daydream so SC-7(9) stays audit-ready without manual scrambles ¹.

Frequently Asked Questions

Does SC-7(9) require blocking all outbound traffic by default?

No. It requires detecting and denying outbound communications that pose a threat to external systems ¹. Most environments allow normal business egress while blocking known malicious destinations and clearly malicious behaviors.

Is DNS sinkholing enough to satisfy the “deny” requirement?

DNS sinkholing can satisfy “deny” for domain-based threats if it reliably prevents the connection and logs the action. You still need coverage for threats that do not depend on DNS (for example, direct-to-IP traffic).

How do we handle encrypted outbound traffic if we can’t inspect TLS?

You can still detect and deny using destination reputation, SNI (where available), DNS signals, JA3/behavioral analytics, and endpoint telemetry. Document the decision not to decrypt in certain contexts and show compensating controls that still block threatening egress.

What counts as “external systems”?

Anything outside your authorization boundary: third-party networks, public internet services, partner environments, and customer systems. Treat partner connections as external unless the boundary documentation explicitly brings them inside your system scope.

How should we treat developers and CI/CD workloads that need broad internet access?

Route their egress through controlled gateways, segment build infrastructure, and use allow-listing for required repos and package registries where feasible. If you must permit broader access, document the exception rationale and add monitoring tuned for scanning and malware callbacks.

What evidence is most persuasive in an assessment?

A clear mapping from policy to enforcement plus proof of deny actions in logs and tickets: rule configurations, blocked event samples, and exception approvals with expirations. Assessors also like to see periodic reviews that result in specific tuning changes ².

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON

2. NIST SP 800-53 Rev. 5