SC-45(1): Synchronization with Authoritative Time Source

SC-45(1): synchronization with authoritative time source requirement means you must regularly compare your systems’ internal clocks against an authoritative time source and take action when drift exceeds your defined tolerance. To operationalize it fast, standardize on approved time sources, enforce NTP/chrony configuration baselines, monitor offset, and retain evidence showing comparisons, exceptions, and remediation ¹.

Key takeaways:

• Define “authoritative time source,” drift thresholds, and comparison frequency per system type, then document them ¹.
• Centralize configuration and monitoring for NTP/chrony across servers, endpoints, network devices, and cloud workloads.
• Keep assessor-ready evidence: configs, monitoring reports, alerts/tickets, and change records proving comparisons happened and drift was corrected.

Time is a security control dependency. If clocks drift, logs stop lining up, incident timelines fall apart, authentication and certificate validation can misbehave, and detection rules that depend on ordering become unreliable. SC-45(1): synchronization with authoritative time source requirement addresses that by requiring you to compare internal system clocks against an authoritative reference and act on the result ¹.

For a CCO, GRC lead, or compliance operator, the goal is simple: make time sync a managed, testable control with clear ownership and recurring evidence. Treat it like patching: define standards, push configuration, monitor continuously, and close the loop with tickets when drift occurs. Your auditors will not be satisfied with “we use NTP” as a statement. They will ask which systems, which sources, what drift threshold, how you know it’s working, and what you do when it isn’t. This page gives requirement-level guidance you can assign to IT operations, security engineering, and system owners, then verify through artifacts and periodic checks aligned to NIST SP 800-53 Rev. 5 ².

Regulatory text

Control enhancement: SC-45(1): Synchronization with Authoritative Time Source
Excerpt: “Compare the internal system clocks {{ insert: param, sc-45.01_odp.01 }} with {{ insert: param, sc-45.01_odp.02 }} ; and” ¹

Operator meaning: You must (1) identify the internal system clocks in scope and (2) compare them to an authoritative time source you trust, on a defined cadence or continuously, and (3) respond to detected time drift according to your procedure. The excerpt is truncated in the catalog view provided, but the implementation expectation is clear: comparisons are required and must be provable with evidence ¹.

Plain-English interpretation (what SC-45(1) requires)

SC-45(1): synchronization with authoritative time source requirement expects that:

• Every in-scope system’s clock is either synchronized to, or at least compared against, an authoritative time source.
• You can detect clock drift and demonstrate that you correct it (or formally accept the risk for exceptions).
• You treat time as a control with governance: approved sources, configuration standards, monitoring, and evidence.

Practically, “compare” should mean an automated check of offset (difference between system time and reference time), with alerting and a ticket when the offset exceeds your tolerance.

Who it applies to (entity and operational context)

Entities: Federal information systems and contractor systems handling federal data are explicit applicability targets in the provided control metadata ¹.

Operational contexts where assessors care most:

• Security monitoring and incident response: Correlation across SIEM, EDR, IDS, cloud logs depends on consistent timestamps.
• Identity and access systems: Authentication flows, Kerberos-like ecosystems, token issuance/validation, and certificate checks can fail or become unreliable if time is wrong.
• Distributed systems: Microservices, message queues, databases, and container clusters need stable time for ordering and debugging.
• Regulated workloads: Any system supporting compliance attestations, investigations, or eDiscovery needs defensible timestamps.

In-scope assets (typical):

• Domain controllers and identity services
• Log sources (servers, endpoints, WAFs, firewalls, VPN, proxies)
• SIEM and log collectors
• Critical applications and databases
• Cloud workloads (VMs, managed Kubernetes nodes, container hosts)
• Network gear that produces security logs

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

Step 1 — Assign ownership and define the “authoritative time source”

1. Name a control owner (often IT Ops or SecEng) and a compliance owner (GRC) who validates evidence and exceptions.
2. Define authoritative time sources you approve (example: internal stratum-1/2 NTP servers, or cloud-provider time services where permitted).
3. Document trust rules: which sources are allowed, how they’re authenticated (where supported), and which networks can reach them.

Deliverable: Time Synchronization Standard (1–2 pages) that includes: approved sources, required protocol(s), drift tolerance targets by asset class, and exception process.

Step 2 — Build an authoritative time architecture (resilient and auditable)

Create a clear topology:

• Reference layer: external authoritative sources (or provider service).
• Internal time tier: your internal NTP servers that sync upstream.
• Clients: systems configured to sync to your internal tier.

Controls to decide and document:

• Redundancy (multiple sources)
• Network segmentation (time sources reachable from restricted networks)
• Configuration management method (GPO, MDM, Ansible, cloud policy, gold images)

Step 3 — Standardize configuration baselines (server, endpoint, network, cloud)

Implement “known good” time configuration per platform. Your baseline should specify:

• Service used (NTP/chrony/systemd-timesyncd or platform equivalent)
• Approved servers/pools (internal time tier)
• Polling behavior and failover settings (platform-specific)
• Startup behavior (sync at boot)
• Logging enabled for time sync events

Make this enforceable:

• Windows: domain time hierarchy settings, GPO enforcement, and monitoring.
• Linux: chrony/ntpd config via config management, immutable settings where appropriate.
• Network devices: NTP server definitions and logging settings in standard templates.
• Cloud: enforce via instance templates, config rules, or image pipelines.

Step 4 — Implement “comparison” monitoring (this is the part auditors probe)

SC-45(1) is satisfied by proving comparison and handling drift ¹. Put monitoring in place that:

• Collects offset and sync status from clients and time servers.
• Alerts when offset exceeds your documented tolerance.
• Produces periodic reports you can hand to an assessor.

Practical options:

• Infrastructure monitoring tools (offset metrics)
• SIEM rules on time service logs
• Scheduled scripts that run chronyc tracking, ntpq -p, or OS equivalents and forward results
• For network devices, periodic config and state pulls (NTP associations)

Step 5 — Define drift handling and exception workflow

Write a short procedure that answers:

• What happens when a system is out of sync?
• Who receives the alert?
• How fast is it triaged based on system criticality?
• What remediation steps are approved (restart service, fix firewall rules, correct config, rebuild VM image, replace faulty hardware clock)?
• When do you open a security incident vs. an ops ticket?

Exceptions must be explicit:

• Air-gapped or highly restricted networks
• Legacy devices without NTP support
• Lab environments (if truly out of compliance scope)

For each exception: record compensating controls (for example, local trusted time server inside the enclave) and a review cadence.

Step 6 — Test, then operationalize recurring evidence

Run a controlled validation:

• Pick representative systems per platform and environment.
• Prove they point to the approved source.
• Force a drift scenario in a test environment and prove the alert-to-ticket chain works.

Then move to steady-state:

• Monitor continuously.
• Review weekly exception queues.
• Review time source health and upstream sync.

Daydream fit (earned mention): If your bottleneck is evidence assembly and control mapping across mixed environments, Daydream can track SC-45(1) ownership, procedures, and recurring evidence requests so the time-sync control stays audit-ready without chasing screenshots every cycle ¹.

Required evidence and artifacts to retain

Keep artifacts that prove design, implementation, and operation:

Design (policy/standards)

• Time Synchronization Standard (authoritative sources, drift thresholds, platforms in scope)
• Network diagram or architecture note showing time source hierarchy

Implementation (config proof)

• Configuration baselines (GPO exports, config management code snippets, approved templates)
• System build/image documentation showing time settings baked in
• Inventory list mapping asset classes to time configuration method

Operation (the “comparison” proof)

• Monitoring dashboards or periodic reports showing offset/sync status
• Alert samples and tickets showing drift detection and remediation
• Change records for time server updates
• Exception register with approvals and reviews

Auditors commonly accept sampled evidence if the sampling method is documented and risk-based.

Common exam/audit questions and hangups

Expect questions like:

• “What is your authoritative time source, and how is it protected?” ¹
• “Show me evidence that systems compare internal clocks to the authoritative source.”
• “What drift threshold triggers action, and where is it documented?”
• “How do you know endpoints and network devices comply, not just servers?”
• “How are exceptions approved and reviewed?”
• “What happens if the time source is unreachable?”

Hangups:

• Teams can show NTP config but cannot show comparison results over time.
• Coverage gaps in SaaS, PaaS, or managed services where time is “provider-managed” but not documented in your control narrative.
• Overreliance on ad hoc screenshots without a repeatable evidence process.

Frequent implementation mistakes (and how to avoid them)

1. Mistake: “We use pool.ntp.org everywhere” without governance.
   Fix: Define approved sources and route clients through internal time servers where feasible. Document the rationale and access controls.

2. Mistake: Time servers exist, but clients don’t consistently point to them.
   Fix: Enforce baselines with policy-as-code, GPO/MDM, and configuration management; validate with compliance scans.

3. Mistake: No defined drift tolerance or response expectation.
   Fix: Set drift thresholds by asset criticality in the standard, then tie alerts to tickets.

4. Mistake: Monitoring only checks “service running,” not offset.
   Fix: Monitor offset and synchronization state; retain trend evidence.

5. Mistake: Exceptions live in email threads.
   Fix: Maintain an exception register with approvals, compensating controls, and periodic review.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for SC-45(1). Treat this as an assessment-readiness control: weak time synchronization frequently becomes a finding because it degrades logging integrity, investigative defensibility, and detection reliability. The direct risk is operational: you may be unable to reconstruct event timelines, correlate multi-system activity, or prove sequence of actions during an incident.

Practical 30/60/90-day execution plan

First 30 days (stabilize scope and standards)

• Assign control owner(s) and publish the Time Synchronization Standard.
• Identify authoritative time sources and document topology (including cloud and restricted networks).
• Build an asset inventory view that tags systems as “time-managed” with method and owner.
• Select monitoring approach for offset comparison and define alert thresholds.

Days 31–60 (implement baselines and monitoring)

• Roll out configuration baselines across primary platforms (Windows, Linux, network devices, cloud images).
• Stand up or harden internal NTP tier (or document provider-managed time where applicable).
• Implement offset monitoring and alert routing to ticketing.
• Start evidence collection: baseline exports, monitoring screenshots/reports, and sample tickets.

Days 61–90 (prove operation and close gaps)

• Run a targeted internal assessment: sample each platform/environment and validate end-to-end evidence.
• Remediate systemic drift causes (firewall rules, broken configs, DHCP option issues, VM host time drift).
• Formalize exception handling and complete the exception register.
• Put SC-45(1) on a recurring evidence calendar in Daydream so evidence stays current between audits ¹.

Frequently Asked Questions

What counts as an “authoritative time source” for SC-45(1)?

A time source you explicitly approve, document, and control access to, so systems can compare their internal clocks against it and you can defend that choice in an assessment ¹.

Is “NTP enabled” enough to pass SC-45(1)?

Usually no. Assessors look for proof of comparison and operational handling of drift, not just a configuration line that says NTP is on ¹.

How do we handle cloud managed services where we can’t set NTP directly?

Document the shared responsibility model in your control narrative, retain provider documentation where available, and focus your evidence on what you control: workload configuration, logging alignment tests, and monitoring for time anomalies.

What evidence is most persuasive to auditors?

A written standard, enforced baselines, and monitoring reports that show offsets over time plus a few tickets demonstrating you corrected drift. Pair that with an exception register for edge cases.

How should we treat isolated or air-gapped networks?

Treat them as a separate enclave. Provide an internal authoritative source inside the enclave or document the compensating approach and track it as a formal exception with review.

Where does Daydream help with SC-45(1)?

Daydream is useful for mapping SC-45(1) to owners, procedures, and recurring evidence artifacts, then keeping those artifacts current for audits and customer reviews ¹.

Footnotes

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

2. NIST SP 800-53 Rev. 5