SI-16: Memory Protection

SI-16: Memory Protection requires you to implement technical controls that prevent unauthorized code execution in system memory, and to be able to prove those controls are in place and working. Operationalize it by defining a standard for memory-protection features, enforcing it through secure configuration and build pipelines, and retaining evidence that coverage matches your system inventory. ¹

Key takeaways:

• Treat SI-16 as an engineering standard plus enforcement, not a policy-only control. ¹
• Scope starts with your system inventory; you cannot evidence memory protection if you cannot show which platforms and workloads are covered. ²
• Audits usually fail on “missing implementation evidence,” so design evidence collection as part of operations. ¹

The si-16: memory protection requirement is straightforward on paper: protect system memory from unauthorized code execution. In practice, it spans OS configuration, compiler and build settings, application hardening, and runtime monitoring, and it breaks most often at the seams between teams.

A Compliance Officer, CCO, or GRC lead can operationalize SI-16 quickly by turning it into: (1) a clear minimum technical baseline by platform (servers, endpoints, containers, mobile, embedded, cloud runtimes), (2) an enforcement mechanism (golden images, configuration management, CI/CD gates), and (3) recurring evidence that maps control coverage to in-scope assets.

This page gives requirement-level implementation guidance: what SI-16 means in plain English, who must comply, the concrete steps to implement and maintain it, and what artifacts you should retain to pass an assessment. Where the NIST excerpt references organization-defined parameters, your job is to define them, document them, and prove consistent execution. ¹

Regulatory text

NIST SP 800-53 SI-16 (Memory Protection): “Implement the following controls to protect the system memory from unauthorized code execution: {{ insert: param, si-16_odp }}.” ¹

What the operator must do with this text

• Interpret the “organization-defined parameter” as a requirement to select and document the specific memory-protection mechanisms you will enforce (for example, OS-level protections, compiler hardening, runtime mitigations).
• Implement the mechanisms across the in-scope system components (hosts, workloads, applications, and supporting services).
• Demonstrate operation by retaining evidence that protections are enabled and exceptions are risk-accepted with compensating controls.

The control text is short because NIST expects you to define the details appropriate to your system and impact level, then implement and assess them. ¹

Plain-English interpretation (what SI-16 is really asking)

You must prevent attackers (or malformed software) from placing or running unauthorized code in memory. This includes common failure modes like:

• Memory corruption leading to execution redirection
• Loading unsigned or unapproved code into a process
• Executing code from memory regions that should be data-only

From a compliance perspective, SI-16 is satisfied when you can show: your platforms have memory-protection features enabled by default, your software is built with memory-hardening settings where applicable, and you can detect or block deviations. ¹

Who SI-16 applies to

Entity scope

• Federal information systems and contractor systems handling federal data that adopt NIST SP 800-53 as a control baseline. ²

Operational scope (where it shows up)

SI-16 is usually assessed for:

• Endpoints and servers (Windows, Linux, macOS)
• Cloud compute (VMs, managed node groups, serverless runtimes where configuration is possible)
• Containers and Kubernetes nodes
• Applications that you build or significantly configure (especially native code, agents, and privileged services)
• Third-party components where you rely on vendor defaults and must manage exceptions

If you cannot configure a managed service’s underlying OS, scope the control to what you can control (build settings, runtime policies, isolation settings) and document shared-responsibility boundaries. ²

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

Step 1: Define your “SI-16 ODP” baseline (the missing parameter)

Create a one-page Memory Protection Standard with:

• In-scope platforms (by environment and workload type)
• Required protections (by platform)
• How to verify (commands, configuration checks, EDR posture, CI/CD checks)
• Exception process (who approves, compensating controls, review cadence)

This document is the heart of SI-16 because the requirement explicitly references organization-defined controls. ¹

Step 2: Map control ownership and operating procedure

Assign named owners for:

• Endpoint/OS engineering (OS baselines, device management)
• Platform/SRE (golden images, hardening, patching pipelines)
• AppSec (compiler and build hardening, dependency governance)
• GRC (scope, evidence, exceptions, assessment support)

A common and effective pattern is to maintain a simple RACI and a runbook for evidence collection. Daydream teams often start by mapping SI-16 to an owner, an implementation procedure, and recurring evidence artifacts so assessments do not stall on “who has proof.” ¹

Step 3: Enforce memory protections through configuration management

Pick the mechanism that matches your fleet:

• Golden images + drift control for servers and VMs
• MDM/endpoint management for endpoints
• Infrastructure-as-code for cloud settings that affect runtime isolation and permissions
• Policy-as-code checks for Kubernetes node and workload security posture

Operational requirement: enforcement must be repeatable. A one-time hardening sprint without drift detection is where SI-16 evidence decays fastest.

Step 4: Bake memory-hardening into build pipelines (where you control code)

For internally developed software, define build requirements that support memory safety and hardening (compiler/linker flags, signed binaries, restrictions on dynamic code loading where feasible). Then:

• Add CI checks that validate the settings are present for release builds.
• Require release artifacts to include a build manifest that records hardening settings.

If you do not control source code (commercial software), treat this as a third-party risk input: document what you can confirm, what is unverifiable, and how you reduce exposure (isolation, least privilege, segmentation). Keep the line clear between “implemented by us” and “assumed by supplier.” ²

Step 5: Monitor and respond to violations

You need a way to detect and act on:

• hosts that fall out of baseline,
• processes that load untrusted modules,
• suspicious memory execution behaviors (as supported by your security tooling).

Tie findings to ticketing with defined SLAs (your choice), and retain closure evidence. SI-16 does not require a specific tool, but assessors will expect you to show you can detect and correct deviations, not only define them. ²

Step 6: Maintain an exception register

Memory protection often has real exceptions (legacy apps, kernel drivers, performance constraints). Manage them explicitly:

• Document the technical reason.
• Document compensating controls (extra monitoring, isolation, restricted access).
• Record approval and periodic review.

Exception discipline is a major differentiator between mature compliance and “we meant to.” ¹

Required evidence and artifacts to retain

Keep evidence aligned to “defined, implemented, operating”:

Definition artifacts

• Memory Protection Standard (your SI-16 ODP definition) ¹
• Scope statement tied to your system boundary and asset inventory ²

Implementation artifacts

• OS baseline configuration documents ¹
• Golden image build records or baseline-as-code repositories
• CI/CD policy configuration for build hardening checks (where applicable)
• Third-party software attestation notes or security documentation you relied on (what you reviewed and when)

Operating effectiveness artifacts

• Sampled configuration scan results showing protections enabled
• Drift/exception reports and remediation tickets
• Monitoring alerts and incident tickets tied to memory-execution or untrusted code events (if your tooling supports it)
• Exception register with approvals and review notes

A practical evidence tactic: maintain a control packet for SI-16 with an index, current baseline, most recent scan output, and exception register export. Daydream can track these recurring artifacts so you do not rebuild the packet for every assessment. ¹

Common exam/audit questions and hangups

1. “What exactly are your SI-16 controls?”
   Hangup: you point to a policy instead of a technical standard plus proof. Provide your ODP baseline and verification method. ¹

2. “Show me which assets are in scope and their compliance status.”
   Hangup: incomplete inventory, or scan coverage doesn’t match inventory. Tie scan coverage to the same asset source of truth. ²

3. “How do you handle exceptions?”
   Hangup: ad hoc waivers in email/Slack. Use a register with approvals and compensating controls. ¹

4. “How do you know controls are still enabled after changes?”
   Hangup: no drift detection or no periodic validation evidence. Provide recurring scan outputs and change records. ²

Frequent implementation mistakes (and how to avoid them)

• Mistake: Treating SI-16 as endpoint-only.
  Fix: include servers, cloud workloads, and container nodes in the baseline and evidence plan. ²

• Mistake: “We enable it by default” with no proof.
  Fix: retain configuration outputs, posture reports, and baseline-as-code commits tied to environments. ¹

• Mistake: Exceptions become permanent.
  Fix: require compensating controls and a formal re-review trigger when apps/platforms change. ²

• Mistake: No ownership across OS, platform, and app layers.
  Fix: assign owners and write a short operating procedure for checks and evidence capture. ¹

Risk implications (why auditors care)

Unauthorized code execution in memory is a common path to privilege escalation, persistence, and lateral movement after an initial foothold. For regulated environments, SI-16 failures translate into:

• higher likelihood of compromise from software vulnerabilities,
• weaker detective controls for post-exploitation behaviors,
• assessment findings that are hard to rebut because they are measurable at configuration level.

NIST frames SI-16 as a system integrity safeguard; treat it as a control that reduces blast radius when other controls fail. ²

Practical 30/60/90-day execution plan

First 30 days: define, scope, and get measurable

• Publish the Memory Protection Standard (your SI-16 ODP content) with platform-specific requirements and verification steps. ¹
• Assign control owners and create the SI-16 evidence checklist (what you will show an assessor). ¹
• Reconcile asset inventory vs. scanning/management coverage; document gaps and an interim approach. ²

By 60 days: enforce and produce repeatable evidence

• Implement or update golden images / endpoint baselines and begin drift reporting.
• Add CI/CD checks for build hardening where you control code; document how releases are validated.
• Stand up the exception register with approval workflow and compensating controls.

By 90 days: operationalize and make it audit-ready

• Produce a SI-16 control packet with the latest evidence set (baseline, scope, scan outputs, exceptions, remediation tickets). ¹
• Run a tabletop assessment with internal audit or a peer review: pick sample assets, reproduce the verification steps, and confirm evidence is retrievable.
• Integrate evidence capture into your GRC workflow. Daydream is a natural fit here because it can track owners, procedures, and recurring artifacts so SI-16 evidence stays current between audits. ¹

Frequently Asked Questions

Do I need to implement the same memory protection mechanisms on every platform?

No. SI-16 expects you to define the controls (the ODP content) that are appropriate per platform and system context, then implement and evidence them. Keep the per-platform baseline explicit so assessors can see the rationale. ¹

How do we handle managed cloud services where we cannot control OS-level memory settings?

Document shared-responsibility boundaries and implement what you can control (configuration, isolation, identity/permissions, and build/runtime settings for your code). Track this as part of the SI-16 scope statement and exception logic where needed. ²

What evidence is usually enough to satisfy an assessor for SI-16?

Assessors typically want to see a defined baseline, proof it is deployed across in-scope assets, and proof deviations are detected and remediated. A control packet with a current scan sample set plus an exception register covers most reviews. ¹

Does SI-16 require a specific security tool like EDR?

No specific tool is named in the excerpt. Choose tools and methods that let you enforce settings and produce reliable evidence that protections are enabled and monitored. ¹

How should we treat third-party software and appliances under SI-16?

Treat them as in-scope components if they process or protect your federal data or sit in your system boundary. If you cannot validate internal memory protections, document what you reviewed, what you rely on from the supplier, and what compensating controls you use. ²

What’s the fastest way to get audit-ready if we’re starting from scratch?

Start by defining the ODP baseline and mapping owners and evidence artifacts, then focus on one enforcement path per platform (golden images, MDM, or configuration management). Tools like Daydream help by keeping the SI-16 owner/procedure/evidence mapping current so you can produce proof on demand. ¹

Footnotes

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

2. NIST SP 800-53 Rev. 5